1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Memory merging support. 4 * 5 * This code enables dynamic sharing of identical pages found in different 6 * memory areas, even if they are not shared by fork() 7 * 8 * Copyright (C) 2008-2009 Red Hat, Inc. 9 * Authors: 10 * Izik Eidus 11 * Andrea Arcangeli 12 * Chris Wright 13 * Hugh Dickins 14 */ 15 16 #include <linux/errno.h> 17 #include <linux/mm.h> 18 #include <linux/mm_inline.h> 19 #include <linux/fs.h> 20 #include <linux/mman.h> 21 #include <linux/sched.h> 22 #include <linux/sched/mm.h> 23 #include <linux/sched/cputime.h> 24 #include <linux/rwsem.h> 25 #include <linux/pagemap.h> 26 #include <linux/rmap.h> 27 #include <linux/spinlock.h> 28 #include <linux/xxhash.h> 29 #include <linux/delay.h> 30 #include <linux/kthread.h> 31 #include <linux/wait.h> 32 #include <linux/slab.h> 33 #include <linux/rbtree.h> 34 #include <linux/memory.h> 35 #include <linux/mmu_notifier.h> 36 #include <linux/swap.h> 37 #include <linux/ksm.h> 38 #include <linux/hashtable.h> 39 #include <linux/freezer.h> 40 #include <linux/oom.h> 41 #include <linux/numa.h> 42 #include <linux/pagewalk.h> 43 44 #include <asm/tlbflush.h> 45 #include "internal.h" 46 #include "mm_slot.h" 47 48 #define CREATE_TRACE_POINTS 49 #include <trace/events/ksm.h> 50 51 #ifdef CONFIG_NUMA 52 #define NUMA(x) (x) 53 #define DO_NUMA(x) do { (x); } while (0) 54 #else 55 #define NUMA(x) (0) 56 #define DO_NUMA(x) do { } while (0) 57 #endif 58 59 typedef u8 rmap_age_t; 60 61 /** 62 * DOC: Overview 63 * 64 * A few notes about the KSM scanning process, 65 * to make it easier to understand the data structures below: 66 * 67 * In order to reduce excessive scanning, KSM sorts the memory pages by their 68 * contents into a data structure that holds pointers to the pages' locations. 69 * 70 * Since the contents of the pages may change at any moment, KSM cannot just 71 * insert the pages into a normal sorted tree and expect it to find anything. 72 * Therefore KSM uses two data structures - the stable and the unstable tree. 73 * 74 * The stable tree holds pointers to all the merged pages (ksm pages), sorted 75 * by their contents. Because each such page is write-protected, searching on 76 * this tree is fully assured to be working (except when pages are unmapped), 77 * and therefore this tree is called the stable tree. 78 * 79 * The stable tree node includes information required for reverse 80 * mapping from a KSM page to virtual addresses that map this page. 81 * 82 * In order to avoid large latencies of the rmap walks on KSM pages, 83 * KSM maintains two types of nodes in the stable tree: 84 * 85 * * the regular nodes that keep the reverse mapping structures in a 86 * linked list 87 * * the "chains" that link nodes ("dups") that represent the same 88 * write protected memory content, but each "dup" corresponds to a 89 * different KSM page copy of that content 90 * 91 * Internally, the regular nodes, "dups" and "chains" are represented 92 * using the same struct ksm_stable_node structure. 93 * 94 * In addition to the stable tree, KSM uses a second data structure called the 95 * unstable tree: this tree holds pointers to pages which have been found to 96 * be "unchanged for a period of time". The unstable tree sorts these pages 97 * by their contents, but since they are not write-protected, KSM cannot rely 98 * upon the unstable tree to work correctly - the unstable tree is liable to 99 * be corrupted as its contents are modified, and so it is called unstable. 100 * 101 * KSM solves this problem by several techniques: 102 * 103 * 1) The unstable tree is flushed every time KSM completes scanning all 104 * memory areas, and then the tree is rebuilt again from the beginning. 105 * 2) KSM will only insert into the unstable tree, pages whose hash value 106 * has not changed since the previous scan of all memory areas. 107 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the 108 * colors of the nodes and not on their contents, assuring that even when 109 * the tree gets "corrupted" it won't get out of balance, so scanning time 110 * remains the same (also, searching and inserting nodes in an rbtree uses 111 * the same algorithm, so we have no overhead when we flush and rebuild). 112 * 4) KSM never flushes the stable tree, which means that even if it were to 113 * take 10 attempts to find a page in the unstable tree, once it is found, 114 * it is secured in the stable tree. (When we scan a new page, we first 115 * compare it against the stable tree, and then against the unstable tree.) 116 * 117 * If the merge_across_nodes tunable is unset, then KSM maintains multiple 118 * stable trees and multiple unstable trees: one of each for each NUMA node. 119 */ 120 121 /** 122 * struct ksm_mm_slot - ksm information per mm that is being scanned 123 * @slot: hash lookup from mm to mm_slot 124 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items 125 */ 126 struct ksm_mm_slot { 127 struct mm_slot slot; 128 struct ksm_rmap_item *rmap_list; 129 }; 130 131 /** 132 * struct ksm_scan - cursor for scanning 133 * @mm_slot: the current mm_slot we are scanning 134 * @address: the next address inside that to be scanned 135 * @rmap_list: link to the next rmap to be scanned in the rmap_list 136 * @seqnr: count of completed full scans (needed when removing unstable node) 137 * 138 * There is only the one ksm_scan instance of this cursor structure. 139 */ 140 struct ksm_scan { 141 struct ksm_mm_slot *mm_slot; 142 unsigned long address; 143 struct ksm_rmap_item **rmap_list; 144 unsigned long seqnr; 145 }; 146 147 /** 148 * struct ksm_stable_node - node of the stable rbtree 149 * @node: rb node of this ksm page in the stable tree 150 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list 151 * @hlist_dup: linked into the stable_node->hlist with a stable_node chain 152 * @list: linked into migrate_nodes, pending placement in the proper node tree 153 * @hlist: hlist head of rmap_items using this ksm page 154 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid) 155 * @chain_prune_time: time of the last full garbage collection 156 * @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN 157 * @nid: NUMA node id of stable tree in which linked (may not match kpfn) 158 */ 159 struct ksm_stable_node { 160 union { 161 struct rb_node node; /* when node of stable tree */ 162 struct { /* when listed for migration */ 163 struct list_head *head; 164 struct { 165 struct hlist_node hlist_dup; 166 struct list_head list; 167 }; 168 }; 169 }; 170 struct hlist_head hlist; 171 union { 172 unsigned long kpfn; 173 unsigned long chain_prune_time; 174 }; 175 /* 176 * STABLE_NODE_CHAIN can be any negative number in 177 * rmap_hlist_len negative range, but better not -1 to be able 178 * to reliably detect underflows. 179 */ 180 #define STABLE_NODE_CHAIN -1024 181 int rmap_hlist_len; 182 #ifdef CONFIG_NUMA 183 int nid; 184 #endif 185 }; 186 187 /** 188 * struct ksm_rmap_item - reverse mapping item for virtual addresses 189 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list 190 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree 191 * @nid: NUMA node id of unstable tree in which linked (may not match page) 192 * @mm: the memory structure this rmap_item is pointing into 193 * @address: the virtual address this rmap_item tracks (+ flags in low bits) 194 * @oldchecksum: previous checksum of the page at that virtual address 195 * @node: rb node of this rmap_item in the unstable tree 196 * @head: pointer to stable_node heading this list in the stable tree 197 * @hlist: link into hlist of rmap_items hanging off that stable_node 198 * @age: number of scan iterations since creation 199 * @remaining_skips: how many scans to skip 200 */ 201 struct ksm_rmap_item { 202 struct ksm_rmap_item *rmap_list; 203 union { 204 struct anon_vma *anon_vma; /* when stable */ 205 #ifdef CONFIG_NUMA 206 int nid; /* when node of unstable tree */ 207 #endif 208 }; 209 struct mm_struct *mm; 210 unsigned long address; /* + low bits used for flags below */ 211 unsigned int oldchecksum; /* when unstable */ 212 rmap_age_t age; 213 rmap_age_t remaining_skips; 214 union { 215 struct rb_node node; /* when node of unstable tree */ 216 struct { /* when listed from stable tree */ 217 struct ksm_stable_node *head; 218 struct hlist_node hlist; 219 }; 220 }; 221 }; 222 223 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ 224 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */ 225 #define STABLE_FLAG 0x200 /* is listed from the stable tree */ 226 227 /* The stable and unstable tree heads */ 228 static struct rb_root one_stable_tree[1] = { RB_ROOT }; 229 static struct rb_root one_unstable_tree[1] = { RB_ROOT }; 230 static struct rb_root *root_stable_tree = one_stable_tree; 231 static struct rb_root *root_unstable_tree = one_unstable_tree; 232 233 /* Recently migrated nodes of stable tree, pending proper placement */ 234 static LIST_HEAD(migrate_nodes); 235 #define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev) 236 237 #define MM_SLOTS_HASH_BITS 10 238 static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS); 239 240 static struct ksm_mm_slot ksm_mm_head = { 241 .slot.mm_node = LIST_HEAD_INIT(ksm_mm_head.slot.mm_node), 242 }; 243 static struct ksm_scan ksm_scan = { 244 .mm_slot = &ksm_mm_head, 245 }; 246 247 static struct kmem_cache *rmap_item_cache; 248 static struct kmem_cache *stable_node_cache; 249 static struct kmem_cache *mm_slot_cache; 250 251 /* Default number of pages to scan per batch */ 252 #define DEFAULT_PAGES_TO_SCAN 100 253 254 /* The number of pages scanned */ 255 static unsigned long ksm_pages_scanned; 256 257 /* The number of nodes in the stable tree */ 258 static unsigned long ksm_pages_shared; 259 260 /* The number of page slots additionally sharing those nodes */ 261 static unsigned long ksm_pages_sharing; 262 263 /* The number of nodes in the unstable tree */ 264 static unsigned long ksm_pages_unshared; 265 266 /* The number of rmap_items in use: to calculate pages_volatile */ 267 static unsigned long ksm_rmap_items; 268 269 /* The number of stable_node chains */ 270 static unsigned long ksm_stable_node_chains; 271 272 /* The number of stable_node dups linked to the stable_node chains */ 273 static unsigned long ksm_stable_node_dups; 274 275 /* Delay in pruning stale stable_node_dups in the stable_node_chains */ 276 static unsigned int ksm_stable_node_chains_prune_millisecs = 2000; 277 278 /* Maximum number of page slots sharing a stable node */ 279 static int ksm_max_page_sharing = 256; 280 281 /* Number of pages ksmd should scan in one batch */ 282 static unsigned int ksm_thread_pages_to_scan = DEFAULT_PAGES_TO_SCAN; 283 284 /* Milliseconds ksmd should sleep between batches */ 285 static unsigned int ksm_thread_sleep_millisecs = 20; 286 287 /* Checksum of an empty (zeroed) page */ 288 static unsigned int zero_checksum __read_mostly; 289 290 /* Whether to merge empty (zeroed) pages with actual zero pages */ 291 static bool ksm_use_zero_pages __read_mostly; 292 293 /* Skip pages that couldn't be de-duplicated previously */ 294 /* Default to true at least temporarily, for testing */ 295 static bool ksm_smart_scan = true; 296 297 /* The number of zero pages which is placed by KSM */ 298 atomic_long_t ksm_zero_pages = ATOMIC_LONG_INIT(0); 299 300 /* The number of pages that have been skipped due to "smart scanning" */ 301 static unsigned long ksm_pages_skipped; 302 303 /* Don't scan more than max pages per batch. */ 304 static unsigned long ksm_advisor_max_pages_to_scan = 30000; 305 306 /* Min CPU for scanning pages per scan */ 307 #define KSM_ADVISOR_MIN_CPU 10 308 309 /* Max CPU for scanning pages per scan */ 310 static unsigned int ksm_advisor_max_cpu = 70; 311 312 /* Target scan time in seconds to analyze all KSM candidate pages. */ 313 static unsigned long ksm_advisor_target_scan_time = 200; 314 315 /* Exponentially weighted moving average. */ 316 #define EWMA_WEIGHT 30 317 318 /** 319 * struct advisor_ctx - metadata for KSM advisor 320 * @start_scan: start time of the current scan 321 * @scan_time: scan time of previous scan 322 * @change: change in percent to pages_to_scan parameter 323 * @cpu_time: cpu time consumed by the ksmd thread in the previous scan 324 */ 325 struct advisor_ctx { 326 ktime_t start_scan; 327 unsigned long scan_time; 328 unsigned long change; 329 unsigned long long cpu_time; 330 }; 331 static struct advisor_ctx advisor_ctx; 332 333 /* Define different advisor's */ 334 enum ksm_advisor_type { 335 KSM_ADVISOR_NONE, 336 KSM_ADVISOR_SCAN_TIME, 337 }; 338 static enum ksm_advisor_type ksm_advisor; 339 340 #ifdef CONFIG_SYSFS 341 /* 342 * Only called through the sysfs control interface: 343 */ 344 345 /* At least scan this many pages per batch. */ 346 static unsigned long ksm_advisor_min_pages_to_scan = 500; 347 348 static void set_advisor_defaults(void) 349 { 350 if (ksm_advisor == KSM_ADVISOR_NONE) { 351 ksm_thread_pages_to_scan = DEFAULT_PAGES_TO_SCAN; 352 } else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) { 353 advisor_ctx = (const struct advisor_ctx){ 0 }; 354 ksm_thread_pages_to_scan = ksm_advisor_min_pages_to_scan; 355 } 356 } 357 #endif /* CONFIG_SYSFS */ 358 359 static inline void advisor_start_scan(void) 360 { 361 if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) 362 advisor_ctx.start_scan = ktime_get(); 363 } 364 365 /* 366 * Use previous scan time if available, otherwise use current scan time as an 367 * approximation for the previous scan time. 368 */ 369 static inline unsigned long prev_scan_time(struct advisor_ctx *ctx, 370 unsigned long scan_time) 371 { 372 return ctx->scan_time ? ctx->scan_time : scan_time; 373 } 374 375 /* Calculate exponential weighted moving average */ 376 static unsigned long ewma(unsigned long prev, unsigned long curr) 377 { 378 return ((100 - EWMA_WEIGHT) * prev + EWMA_WEIGHT * curr) / 100; 379 } 380 381 /* 382 * The scan time advisor is based on the current scan rate and the target 383 * scan rate. 384 * 385 * new_pages_to_scan = pages_to_scan * (scan_time / target_scan_time) 386 * 387 * To avoid perturbations it calculates a change factor of previous changes. 388 * A new change factor is calculated for each iteration and it uses an 389 * exponentially weighted moving average. The new pages_to_scan value is 390 * multiplied with that change factor: 391 * 392 * new_pages_to_scan *= change factor 393 * 394 * The new_pages_to_scan value is limited by the cpu min and max values. It 395 * calculates the cpu percent for the last scan and calculates the new 396 * estimated cpu percent cost for the next scan. That value is capped by the 397 * cpu min and max setting. 398 * 399 * In addition the new pages_to_scan value is capped by the max and min 400 * limits. 401 */ 402 static void scan_time_advisor(void) 403 { 404 unsigned int cpu_percent; 405 unsigned long cpu_time; 406 unsigned long cpu_time_diff; 407 unsigned long cpu_time_diff_ms; 408 unsigned long pages; 409 unsigned long per_page_cost; 410 unsigned long factor; 411 unsigned long change; 412 unsigned long last_scan_time; 413 unsigned long scan_time; 414 415 /* Convert scan time to seconds */ 416 scan_time = div_s64(ktime_ms_delta(ktime_get(), advisor_ctx.start_scan), 417 MSEC_PER_SEC); 418 scan_time = scan_time ? scan_time : 1; 419 420 /* Calculate CPU consumption of ksmd background thread */ 421 cpu_time = task_sched_runtime(current); 422 cpu_time_diff = cpu_time - advisor_ctx.cpu_time; 423 cpu_time_diff_ms = cpu_time_diff / 1000 / 1000; 424 425 cpu_percent = (cpu_time_diff_ms * 100) / (scan_time * 1000); 426 cpu_percent = cpu_percent ? cpu_percent : 1; 427 last_scan_time = prev_scan_time(&advisor_ctx, scan_time); 428 429 /* Calculate scan time as percentage of target scan time */ 430 factor = ksm_advisor_target_scan_time * 100 / scan_time; 431 factor = factor ? factor : 1; 432 433 /* 434 * Calculate scan time as percentage of last scan time and use 435 * exponentially weighted average to smooth it 436 */ 437 change = scan_time * 100 / last_scan_time; 438 change = change ? change : 1; 439 change = ewma(advisor_ctx.change, change); 440 441 /* Calculate new scan rate based on target scan rate. */ 442 pages = ksm_thread_pages_to_scan * 100 / factor; 443 /* Update pages_to_scan by weighted change percentage. */ 444 pages = pages * change / 100; 445 446 /* Cap new pages_to_scan value */ 447 per_page_cost = ksm_thread_pages_to_scan / cpu_percent; 448 per_page_cost = per_page_cost ? per_page_cost : 1; 449 450 pages = min(pages, per_page_cost * ksm_advisor_max_cpu); 451 pages = max(pages, per_page_cost * KSM_ADVISOR_MIN_CPU); 452 pages = min(pages, ksm_advisor_max_pages_to_scan); 453 454 /* Update advisor context */ 455 advisor_ctx.change = change; 456 advisor_ctx.scan_time = scan_time; 457 advisor_ctx.cpu_time = cpu_time; 458 459 ksm_thread_pages_to_scan = pages; 460 trace_ksm_advisor(scan_time, pages, cpu_percent); 461 } 462 463 static void advisor_stop_scan(void) 464 { 465 if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) 466 scan_time_advisor(); 467 } 468 469 #ifdef CONFIG_NUMA 470 /* Zeroed when merging across nodes is not allowed */ 471 static unsigned int ksm_merge_across_nodes = 1; 472 static int ksm_nr_node_ids = 1; 473 #else 474 #define ksm_merge_across_nodes 1U 475 #define ksm_nr_node_ids 1 476 #endif 477 478 #define KSM_RUN_STOP 0 479 #define KSM_RUN_MERGE 1 480 #define KSM_RUN_UNMERGE 2 481 #define KSM_RUN_OFFLINE 4 482 static unsigned long ksm_run = KSM_RUN_STOP; 483 static void wait_while_offlining(void); 484 485 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait); 486 static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait); 487 static DEFINE_MUTEX(ksm_thread_mutex); 488 static DEFINE_SPINLOCK(ksm_mmlist_lock); 489 490 static int __init ksm_slab_init(void) 491 { 492 rmap_item_cache = KMEM_CACHE(ksm_rmap_item, 0); 493 if (!rmap_item_cache) 494 goto out; 495 496 stable_node_cache = KMEM_CACHE(ksm_stable_node, 0); 497 if (!stable_node_cache) 498 goto out_free1; 499 500 mm_slot_cache = KMEM_CACHE(ksm_mm_slot, 0); 501 if (!mm_slot_cache) 502 goto out_free2; 503 504 return 0; 505 506 out_free2: 507 kmem_cache_destroy(stable_node_cache); 508 out_free1: 509 kmem_cache_destroy(rmap_item_cache); 510 out: 511 return -ENOMEM; 512 } 513 514 static void __init ksm_slab_free(void) 515 { 516 kmem_cache_destroy(mm_slot_cache); 517 kmem_cache_destroy(stable_node_cache); 518 kmem_cache_destroy(rmap_item_cache); 519 mm_slot_cache = NULL; 520 } 521 522 static __always_inline bool is_stable_node_chain(struct ksm_stable_node *chain) 523 { 524 return chain->rmap_hlist_len == STABLE_NODE_CHAIN; 525 } 526 527 static __always_inline bool is_stable_node_dup(struct ksm_stable_node *dup) 528 { 529 return dup->head == STABLE_NODE_DUP_HEAD; 530 } 531 532 static inline void stable_node_chain_add_dup(struct ksm_stable_node *dup, 533 struct ksm_stable_node *chain) 534 { 535 VM_BUG_ON(is_stable_node_dup(dup)); 536 dup->head = STABLE_NODE_DUP_HEAD; 537 VM_BUG_ON(!is_stable_node_chain(chain)); 538 hlist_add_head(&dup->hlist_dup, &chain->hlist); 539 ksm_stable_node_dups++; 540 } 541 542 static inline void __stable_node_dup_del(struct ksm_stable_node *dup) 543 { 544 VM_BUG_ON(!is_stable_node_dup(dup)); 545 hlist_del(&dup->hlist_dup); 546 ksm_stable_node_dups--; 547 } 548 549 static inline void stable_node_dup_del(struct ksm_stable_node *dup) 550 { 551 VM_BUG_ON(is_stable_node_chain(dup)); 552 if (is_stable_node_dup(dup)) 553 __stable_node_dup_del(dup); 554 else 555 rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid)); 556 #ifdef CONFIG_DEBUG_VM 557 dup->head = NULL; 558 #endif 559 } 560 561 static inline struct ksm_rmap_item *alloc_rmap_item(void) 562 { 563 struct ksm_rmap_item *rmap_item; 564 565 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL | 566 __GFP_NORETRY | __GFP_NOWARN); 567 if (rmap_item) 568 ksm_rmap_items++; 569 return rmap_item; 570 } 571 572 static inline void free_rmap_item(struct ksm_rmap_item *rmap_item) 573 { 574 ksm_rmap_items--; 575 rmap_item->mm->ksm_rmap_items--; 576 rmap_item->mm = NULL; /* debug safety */ 577 kmem_cache_free(rmap_item_cache, rmap_item); 578 } 579 580 static inline struct ksm_stable_node *alloc_stable_node(void) 581 { 582 /* 583 * The allocation can take too long with GFP_KERNEL when memory is under 584 * pressure, which may lead to hung task warnings. Adding __GFP_HIGH 585 * grants access to memory reserves, helping to avoid this problem. 586 */ 587 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH); 588 } 589 590 static inline void free_stable_node(struct ksm_stable_node *stable_node) 591 { 592 VM_BUG_ON(stable_node->rmap_hlist_len && 593 !is_stable_node_chain(stable_node)); 594 kmem_cache_free(stable_node_cache, stable_node); 595 } 596 597 /* 598 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's 599 * page tables after it has passed through ksm_exit() - which, if necessary, 600 * takes mmap_lock briefly to serialize against them. ksm_exit() does not set 601 * a special flag: they can just back out as soon as mm_users goes to zero. 602 * ksm_test_exit() is used throughout to make this test for exit: in some 603 * places for correctness, in some places just to avoid unnecessary work. 604 */ 605 static inline bool ksm_test_exit(struct mm_struct *mm) 606 { 607 return atomic_read(&mm->mm_users) == 0; 608 } 609 610 static int break_ksm_pmd_entry(pmd_t *pmdp, unsigned long addr, unsigned long end, 611 struct mm_walk *walk) 612 { 613 unsigned long *found_addr = (unsigned long *) walk->private; 614 struct mm_struct *mm = walk->mm; 615 pte_t *start_ptep, *ptep; 616 spinlock_t *ptl; 617 int found = 0; 618 619 if (ksm_test_exit(walk->mm)) 620 return 0; 621 if (signal_pending(current)) 622 return -ERESTARTSYS; 623 624 start_ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); 625 if (!start_ptep) 626 return 0; 627 628 for (ptep = start_ptep; addr < end; ptep++, addr += PAGE_SIZE) { 629 pte_t pte = ptep_get(ptep); 630 struct folio *folio = NULL; 631 632 if (pte_present(pte)) { 633 folio = vm_normal_folio(walk->vma, addr, pte); 634 } else if (!pte_none(pte)) { 635 const softleaf_t entry = softleaf_from_pte(pte); 636 637 /* 638 * As KSM pages remain KSM pages until freed, no need to wait 639 * here for migration to end. 640 */ 641 if (softleaf_is_migration(entry)) 642 folio = softleaf_to_folio(entry); 643 } 644 /* return 1 if the page is an normal ksm page or KSM-placed zero page */ 645 found = (folio && folio_test_ksm(folio)) || 646 (pte_present(pte) && is_ksm_zero_pte(pte)); 647 if (found) { 648 *found_addr = addr; 649 goto out_unlock; 650 } 651 } 652 out_unlock: 653 pte_unmap_unlock(ptep, ptl); 654 return found; 655 } 656 657 static const struct mm_walk_ops break_ksm_ops = { 658 .pmd_entry = break_ksm_pmd_entry, 659 .walk_lock = PGWALK_RDLOCK, 660 }; 661 662 static const struct mm_walk_ops break_ksm_lock_vma_ops = { 663 .pmd_entry = break_ksm_pmd_entry, 664 .walk_lock = PGWALK_WRLOCK, 665 }; 666 667 /* 668 * Though it's very tempting to unmerge rmap_items from stable tree rather 669 * than check every pte of a given vma, the locking doesn't quite work for 670 * that - an rmap_item is assigned to the stable tree after inserting ksm 671 * page and upping mmap_lock. Nor does it fit with the way we skip dup'ing 672 * rmap_items from parent to child at fork time (so as not to waste time 673 * if exit comes before the next scan reaches it). 674 * 675 * Similarly, although we'd like to remove rmap_items (so updating counts 676 * and freeing memory) when unmerging an area, it's easier to leave that 677 * to the next pass of ksmd - consider, for example, how ksmd might be 678 * in cmp_and_merge_page on one of the rmap_items we would be removing. 679 * 680 * We use break_ksm to break COW on a ksm page by triggering unsharing, 681 * such that the ksm page will get replaced by an exclusive anonymous page. 682 * 683 * We take great care only to touch a ksm page, in a VM_MERGEABLE vma, 684 * in case the application has unmapped and remapped mm,addr meanwhile. 685 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP 686 * mmap of /dev/mem, where we would not want to touch it. 687 * 688 * FAULT_FLAG_REMOTE/FOLL_REMOTE are because we do this outside the context 689 * of the process that owns 'vma'. We also do not want to enforce 690 * protection keys here anyway. 691 */ 692 static int break_ksm(struct vm_area_struct *vma, unsigned long addr, 693 unsigned long end, bool lock_vma) 694 { 695 vm_fault_t ret = 0; 696 const struct mm_walk_ops *ops = lock_vma ? 697 &break_ksm_lock_vma_ops : &break_ksm_ops; 698 699 do { 700 int ksm_page; 701 702 cond_resched(); 703 ksm_page = walk_page_range_vma(vma, addr, end, ops, &addr); 704 if (ksm_page <= 0) 705 return ksm_page; 706 ret = handle_mm_fault(vma, addr, 707 FAULT_FLAG_UNSHARE | FAULT_FLAG_REMOTE, 708 NULL); 709 } while (!(ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM))); 710 /* 711 * We must loop until we no longer find a KSM page because 712 * handle_mm_fault() may back out if there's any difficulty e.g. if 713 * pte accessed bit gets updated concurrently. 714 * 715 * VM_FAULT_SIGBUS could occur if we race with truncation of the 716 * backing file, which also invalidates anonymous pages: that's 717 * okay, that truncation will have unmapped the KSM page for us. 718 * 719 * VM_FAULT_OOM: at the time of writing (late July 2009), setting 720 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the 721 * current task has TIF_MEMDIE set, and will be OOM killed on return 722 * to user; and ksmd, having no mm, would never be chosen for that. 723 * 724 * But if the mm is in a limited mem_cgroup, then the fault may fail 725 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and 726 * even ksmd can fail in this way - though it's usually breaking ksm 727 * just to undo a merge it made a moment before, so unlikely to oom. 728 * 729 * That's a pity: we might therefore have more kernel pages allocated 730 * than we're counting as nodes in the stable tree; but ksm_do_scan 731 * will retry to break_cow on each pass, so should recover the page 732 * in due course. The important thing is to not let VM_MERGEABLE 733 * be cleared while any such pages might remain in the area. 734 */ 735 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; 736 } 737 738 static bool ksm_compatible(const struct file *file, vm_flags_t vm_flags) 739 { 740 if (vm_flags & (VM_SHARED | VM_MAYSHARE | VM_SPECIAL | 741 VM_HUGETLB | VM_DROPPABLE)) 742 return false; /* just ignore the advice */ 743 744 if (file_is_dax(file)) 745 return false; 746 747 #ifdef VM_SAO 748 if (vm_flags & VM_SAO) 749 return false; 750 #endif 751 #ifdef VM_SPARC_ADI 752 if (vm_flags & VM_SPARC_ADI) 753 return false; 754 #endif 755 756 return true; 757 } 758 759 static bool vma_ksm_compatible(struct vm_area_struct *vma) 760 { 761 return ksm_compatible(vma->vm_file, vma->vm_flags); 762 } 763 764 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm, 765 unsigned long addr) 766 { 767 struct vm_area_struct *vma; 768 if (ksm_test_exit(mm)) 769 return NULL; 770 vma = vma_lookup(mm, addr); 771 if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) 772 return NULL; 773 return vma; 774 } 775 776 static void break_cow(struct ksm_rmap_item *rmap_item) 777 { 778 struct mm_struct *mm = rmap_item->mm; 779 unsigned long addr = rmap_item->address; 780 struct vm_area_struct *vma; 781 782 /* 783 * It is not an accident that whenever we want to break COW 784 * to undo, we also need to drop a reference to the anon_vma. 785 */ 786 put_anon_vma(rmap_item->anon_vma); 787 788 mmap_read_lock(mm); 789 vma = find_mergeable_vma(mm, addr); 790 if (vma) 791 break_ksm(vma, addr, addr + PAGE_SIZE, false); 792 mmap_read_unlock(mm); 793 } 794 795 static struct page *get_mergeable_page(struct ksm_rmap_item *rmap_item) 796 { 797 struct mm_struct *mm = rmap_item->mm; 798 unsigned long addr = rmap_item->address; 799 struct vm_area_struct *vma; 800 struct page *page = NULL; 801 struct folio_walk fw; 802 struct folio *folio; 803 804 mmap_read_lock(mm); 805 vma = find_mergeable_vma(mm, addr); 806 if (!vma) 807 goto out; 808 809 folio = folio_walk_start(&fw, vma, addr, 0); 810 if (folio) { 811 if (!folio_is_zone_device(folio) && 812 folio_test_anon(folio)) { 813 folio_get(folio); 814 page = fw.page; 815 } 816 folio_walk_end(&fw, vma); 817 } 818 out: 819 if (page) { 820 flush_anon_page(vma, page, addr); 821 flush_dcache_page(page); 822 } 823 mmap_read_unlock(mm); 824 return page; 825 } 826 827 /* 828 * This helper is used for getting right index into array of tree roots. 829 * When merge_across_nodes knob is set to 1, there are only two rb-trees for 830 * stable and unstable pages from all nodes with roots in index 0. Otherwise, 831 * every node has its own stable and unstable tree. 832 */ 833 static inline int get_kpfn_nid(unsigned long kpfn) 834 { 835 return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn)); 836 } 837 838 static struct ksm_stable_node *alloc_stable_node_chain(struct ksm_stable_node *dup, 839 struct rb_root *root) 840 { 841 struct ksm_stable_node *chain = alloc_stable_node(); 842 VM_BUG_ON(is_stable_node_chain(dup)); 843 if (likely(chain)) { 844 INIT_HLIST_HEAD(&chain->hlist); 845 chain->chain_prune_time = jiffies; 846 chain->rmap_hlist_len = STABLE_NODE_CHAIN; 847 #if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA) 848 chain->nid = NUMA_NO_NODE; /* debug */ 849 #endif 850 ksm_stable_node_chains++; 851 852 /* 853 * Put the stable node chain in the first dimension of 854 * the stable tree and at the same time remove the old 855 * stable node. 856 */ 857 rb_replace_node(&dup->node, &chain->node, root); 858 859 /* 860 * Move the old stable node to the second dimension 861 * queued in the hlist_dup. The invariant is that all 862 * dup stable_nodes in the chain->hlist point to pages 863 * that are write protected and have the exact same 864 * content. 865 */ 866 stable_node_chain_add_dup(dup, chain); 867 } 868 return chain; 869 } 870 871 static inline void free_stable_node_chain(struct ksm_stable_node *chain, 872 struct rb_root *root) 873 { 874 rb_erase(&chain->node, root); 875 free_stable_node(chain); 876 ksm_stable_node_chains--; 877 } 878 879 static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node) 880 { 881 struct ksm_rmap_item *rmap_item; 882 883 /* check it's not STABLE_NODE_CHAIN or negative */ 884 BUG_ON(stable_node->rmap_hlist_len < 0); 885 886 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { 887 if (rmap_item->hlist.next) { 888 ksm_pages_sharing--; 889 trace_ksm_remove_rmap_item(stable_node->kpfn, rmap_item, rmap_item->mm); 890 } else { 891 ksm_pages_shared--; 892 } 893 894 rmap_item->mm->ksm_merging_pages--; 895 896 VM_BUG_ON(stable_node->rmap_hlist_len <= 0); 897 stable_node->rmap_hlist_len--; 898 put_anon_vma(rmap_item->anon_vma); 899 rmap_item->address &= PAGE_MASK; 900 cond_resched(); 901 } 902 903 /* 904 * We need the second aligned pointer of the migrate_nodes 905 * list_head to stay clear from the rb_parent_color union 906 * (aligned and different than any node) and also different 907 * from &migrate_nodes. This will verify that future list.h changes 908 * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it. 909 */ 910 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes); 911 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1); 912 913 trace_ksm_remove_ksm_page(stable_node->kpfn); 914 if (stable_node->head == &migrate_nodes) 915 list_del(&stable_node->list); 916 else 917 stable_node_dup_del(stable_node); 918 free_stable_node(stable_node); 919 } 920 921 enum ksm_get_folio_flags { 922 KSM_GET_FOLIO_NOLOCK, 923 KSM_GET_FOLIO_LOCK, 924 KSM_GET_FOLIO_TRYLOCK 925 }; 926 927 /* 928 * ksm_get_folio: checks if the page indicated by the stable node 929 * is still its ksm page, despite having held no reference to it. 930 * In which case we can trust the content of the page, and it 931 * returns the gotten page; but if the page has now been zapped, 932 * remove the stale node from the stable tree and return NULL. 933 * But beware, the stable node's page might be being migrated. 934 * 935 * You would expect the stable_node to hold a reference to the ksm page. 936 * But if it increments the page's count, swapping out has to wait for 937 * ksmd to come around again before it can free the page, which may take 938 * seconds or even minutes: much too unresponsive. So instead we use a 939 * "keyhole reference": access to the ksm page from the stable node peeps 940 * out through its keyhole to see if that page still holds the right key, 941 * pointing back to this stable node. This relies on freeing a PageAnon 942 * page to reset its page->mapping to NULL, and relies on no other use of 943 * a page to put something that might look like our key in page->mapping. 944 * is on its way to being freed; but it is an anomaly to bear in mind. 945 */ 946 static struct folio *ksm_get_folio(struct ksm_stable_node *stable_node, 947 enum ksm_get_folio_flags flags) 948 { 949 struct folio *folio; 950 void *expected_mapping; 951 unsigned long kpfn; 952 953 expected_mapping = (void *)((unsigned long)stable_node | 954 FOLIO_MAPPING_KSM); 955 again: 956 kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */ 957 folio = pfn_folio(kpfn); 958 if (READ_ONCE(folio->mapping) != expected_mapping) 959 goto stale; 960 961 /* 962 * We cannot do anything with the page while its refcount is 0. 963 * Usually 0 means free, or tail of a higher-order page: in which 964 * case this node is no longer referenced, and should be freed; 965 * however, it might mean that the page is under page_ref_freeze(). 966 * The __remove_mapping() case is easy, again the node is now stale; 967 * the same is in reuse_ksm_page() case; but if page is swapcache 968 * in folio_migrate_mapping(), it might still be our page, 969 * in which case it's essential to keep the node. 970 */ 971 while (!folio_try_get(folio)) { 972 /* 973 * Another check for folio->mapping != expected_mapping 974 * would work here too. We have chosen to test the 975 * swapcache flag to optimize the common case, when the 976 * folio is or is about to be freed: the swapcache flag 977 * is cleared (under spin_lock_irq) in the ref_freeze 978 * section of __remove_mapping(); but anon folio->mapping 979 * is reset to NULL later, in free_pages_prepare(). 980 */ 981 if (!folio_test_swapcache(folio)) 982 goto stale; 983 cpu_relax(); 984 } 985 986 if (READ_ONCE(folio->mapping) != expected_mapping) { 987 folio_put(folio); 988 goto stale; 989 } 990 991 if (flags == KSM_GET_FOLIO_TRYLOCK) { 992 if (!folio_trylock(folio)) { 993 folio_put(folio); 994 return ERR_PTR(-EBUSY); 995 } 996 } else if (flags == KSM_GET_FOLIO_LOCK) 997 folio_lock(folio); 998 999 if (flags != KSM_GET_FOLIO_NOLOCK) { 1000 if (READ_ONCE(folio->mapping) != expected_mapping) { 1001 folio_unlock(folio); 1002 folio_put(folio); 1003 goto stale; 1004 } 1005 } 1006 return folio; 1007 1008 stale: 1009 /* 1010 * We come here from above when folio->mapping or the swapcache flag 1011 * suggests that the node is stale; but it might be under migration. 1012 * We need smp_rmb(), matching the smp_wmb() in folio_migrate_ksm(), 1013 * before checking whether node->kpfn has been changed. 1014 */ 1015 smp_rmb(); 1016 if (READ_ONCE(stable_node->kpfn) != kpfn) 1017 goto again; 1018 remove_node_from_stable_tree(stable_node); 1019 return NULL; 1020 } 1021 1022 /* 1023 * Removing rmap_item from stable or unstable tree. 1024 * This function will clean the information from the stable/unstable tree. 1025 */ 1026 static void remove_rmap_item_from_tree(struct ksm_rmap_item *rmap_item) 1027 { 1028 if (rmap_item->address & STABLE_FLAG) { 1029 struct ksm_stable_node *stable_node; 1030 struct folio *folio; 1031 1032 stable_node = rmap_item->head; 1033 folio = ksm_get_folio(stable_node, KSM_GET_FOLIO_LOCK); 1034 if (!folio) 1035 goto out; 1036 1037 hlist_del(&rmap_item->hlist); 1038 folio_unlock(folio); 1039 folio_put(folio); 1040 1041 if (!hlist_empty(&stable_node->hlist)) 1042 ksm_pages_sharing--; 1043 else 1044 ksm_pages_shared--; 1045 1046 rmap_item->mm->ksm_merging_pages--; 1047 1048 VM_BUG_ON(stable_node->rmap_hlist_len <= 0); 1049 stable_node->rmap_hlist_len--; 1050 1051 put_anon_vma(rmap_item->anon_vma); 1052 rmap_item->head = NULL; 1053 rmap_item->address &= PAGE_MASK; 1054 1055 } else if (rmap_item->address & UNSTABLE_FLAG) { 1056 unsigned char age; 1057 /* 1058 * Usually ksmd can and must skip the rb_erase, because 1059 * root_unstable_tree was already reset to RB_ROOT. 1060 * But be careful when an mm is exiting: do the rb_erase 1061 * if this rmap_item was inserted by this scan, rather 1062 * than left over from before. 1063 */ 1064 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); 1065 BUG_ON(age > 1); 1066 if (!age) 1067 rb_erase(&rmap_item->node, 1068 root_unstable_tree + NUMA(rmap_item->nid)); 1069 ksm_pages_unshared--; 1070 rmap_item->address &= PAGE_MASK; 1071 } 1072 out: 1073 cond_resched(); /* we're called from many long loops */ 1074 } 1075 1076 static void remove_trailing_rmap_items(struct ksm_rmap_item **rmap_list) 1077 { 1078 while (*rmap_list) { 1079 struct ksm_rmap_item *rmap_item = *rmap_list; 1080 *rmap_list = rmap_item->rmap_list; 1081 remove_rmap_item_from_tree(rmap_item); 1082 free_rmap_item(rmap_item); 1083 } 1084 } 1085 1086 static inline 1087 struct ksm_stable_node *folio_stable_node(const struct folio *folio) 1088 { 1089 return folio_test_ksm(folio) ? folio_raw_mapping(folio) : NULL; 1090 } 1091 1092 static inline void folio_set_stable_node(struct folio *folio, 1093 struct ksm_stable_node *stable_node) 1094 { 1095 VM_WARN_ON_FOLIO(folio_test_anon(folio) && PageAnonExclusive(&folio->page), folio); 1096 folio->mapping = (void *)((unsigned long)stable_node | FOLIO_MAPPING_KSM); 1097 } 1098 1099 #ifdef CONFIG_SYSFS 1100 /* 1101 * Only called through the sysfs control interface: 1102 */ 1103 static int remove_stable_node(struct ksm_stable_node *stable_node) 1104 { 1105 struct folio *folio; 1106 int err; 1107 1108 folio = ksm_get_folio(stable_node, KSM_GET_FOLIO_LOCK); 1109 if (!folio) { 1110 /* 1111 * ksm_get_folio did remove_node_from_stable_tree itself. 1112 */ 1113 return 0; 1114 } 1115 1116 /* 1117 * Page could be still mapped if this races with __mmput() running in 1118 * between ksm_exit() and exit_mmap(). Just refuse to let 1119 * merge_across_nodes/max_page_sharing be switched. 1120 */ 1121 err = -EBUSY; 1122 if (!folio_mapped(folio)) { 1123 /* 1124 * The stable node did not yet appear stale to ksm_get_folio(), 1125 * since that allows for an unmapped ksm folio to be recognized 1126 * right up until it is freed; but the node is safe to remove. 1127 * This folio might be in an LRU cache waiting to be freed, 1128 * or it might be in the swapcache (perhaps under writeback), 1129 * or it might have been removed from swapcache a moment ago. 1130 */ 1131 folio_set_stable_node(folio, NULL); 1132 remove_node_from_stable_tree(stable_node); 1133 err = 0; 1134 } 1135 1136 folio_unlock(folio); 1137 folio_put(folio); 1138 return err; 1139 } 1140 1141 static int remove_stable_node_chain(struct ksm_stable_node *stable_node, 1142 struct rb_root *root) 1143 { 1144 struct ksm_stable_node *dup; 1145 struct hlist_node *hlist_safe; 1146 1147 if (!is_stable_node_chain(stable_node)) { 1148 VM_BUG_ON(is_stable_node_dup(stable_node)); 1149 if (remove_stable_node(stable_node)) 1150 return true; 1151 else 1152 return false; 1153 } 1154 1155 hlist_for_each_entry_safe(dup, hlist_safe, 1156 &stable_node->hlist, hlist_dup) { 1157 VM_BUG_ON(!is_stable_node_dup(dup)); 1158 if (remove_stable_node(dup)) 1159 return true; 1160 } 1161 BUG_ON(!hlist_empty(&stable_node->hlist)); 1162 free_stable_node_chain(stable_node, root); 1163 return false; 1164 } 1165 1166 static int remove_all_stable_nodes(void) 1167 { 1168 struct ksm_stable_node *stable_node, *next; 1169 int nid; 1170 int err = 0; 1171 1172 for (nid = 0; nid < ksm_nr_node_ids; nid++) { 1173 while (root_stable_tree[nid].rb_node) { 1174 stable_node = rb_entry(root_stable_tree[nid].rb_node, 1175 struct ksm_stable_node, node); 1176 if (remove_stable_node_chain(stable_node, 1177 root_stable_tree + nid)) { 1178 err = -EBUSY; 1179 break; /* proceed to next nid */ 1180 } 1181 cond_resched(); 1182 } 1183 } 1184 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) { 1185 if (remove_stable_node(stable_node)) 1186 err = -EBUSY; 1187 cond_resched(); 1188 } 1189 return err; 1190 } 1191 1192 static int unmerge_and_remove_all_rmap_items(void) 1193 { 1194 struct ksm_mm_slot *mm_slot; 1195 struct mm_slot *slot; 1196 struct mm_struct *mm; 1197 struct vm_area_struct *vma; 1198 int err = 0; 1199 1200 spin_lock(&ksm_mmlist_lock); 1201 slot = list_entry(ksm_mm_head.slot.mm_node.next, 1202 struct mm_slot, mm_node); 1203 ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); 1204 spin_unlock(&ksm_mmlist_lock); 1205 1206 for (mm_slot = ksm_scan.mm_slot; mm_slot != &ksm_mm_head; 1207 mm_slot = ksm_scan.mm_slot) { 1208 VMA_ITERATOR(vmi, mm_slot->slot.mm, 0); 1209 1210 mm = mm_slot->slot.mm; 1211 mmap_read_lock(mm); 1212 1213 /* 1214 * Exit right away if mm is exiting to avoid lockdep issue in 1215 * the maple tree 1216 */ 1217 if (ksm_test_exit(mm)) 1218 goto mm_exiting; 1219 1220 for_each_vma(vmi, vma) { 1221 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) 1222 continue; 1223 err = break_ksm(vma, vma->vm_start, vma->vm_end, false); 1224 if (err) 1225 goto error; 1226 } 1227 1228 mm_exiting: 1229 remove_trailing_rmap_items(&mm_slot->rmap_list); 1230 mmap_read_unlock(mm); 1231 1232 spin_lock(&ksm_mmlist_lock); 1233 slot = list_entry(mm_slot->slot.mm_node.next, 1234 struct mm_slot, mm_node); 1235 ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); 1236 if (ksm_test_exit(mm)) { 1237 hash_del(&mm_slot->slot.hash); 1238 list_del(&mm_slot->slot.mm_node); 1239 spin_unlock(&ksm_mmlist_lock); 1240 1241 mm_slot_free(mm_slot_cache, mm_slot); 1242 mm_flags_clear(MMF_VM_MERGEABLE, mm); 1243 mm_flags_clear(MMF_VM_MERGE_ANY, mm); 1244 mmdrop(mm); 1245 } else 1246 spin_unlock(&ksm_mmlist_lock); 1247 } 1248 1249 /* Clean up stable nodes, but don't worry if some are still busy */ 1250 remove_all_stable_nodes(); 1251 ksm_scan.seqnr = 0; 1252 return 0; 1253 1254 error: 1255 mmap_read_unlock(mm); 1256 spin_lock(&ksm_mmlist_lock); 1257 ksm_scan.mm_slot = &ksm_mm_head; 1258 spin_unlock(&ksm_mmlist_lock); 1259 return err; 1260 } 1261 #endif /* CONFIG_SYSFS */ 1262 1263 static u32 calc_checksum(struct page *page) 1264 { 1265 u32 checksum; 1266 void *addr = kmap_local_page(page); 1267 checksum = xxhash(addr, PAGE_SIZE, 0); 1268 kunmap_local(addr); 1269 return checksum; 1270 } 1271 1272 static int write_protect_page(struct vm_area_struct *vma, struct folio *folio, 1273 pte_t *orig_pte) 1274 { 1275 struct mm_struct *mm = vma->vm_mm; 1276 DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, 0, 0); 1277 int swapped; 1278 int err = -EFAULT; 1279 struct mmu_notifier_range range; 1280 bool anon_exclusive; 1281 pte_t entry; 1282 1283 if (WARN_ON_ONCE(folio_test_large(folio))) 1284 return err; 1285 1286 pvmw.address = page_address_in_vma(folio, folio_page(folio, 0), vma); 1287 if (pvmw.address == -EFAULT) 1288 goto out; 1289 1290 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, pvmw.address, 1291 pvmw.address + PAGE_SIZE); 1292 mmu_notifier_invalidate_range_start(&range); 1293 1294 if (!page_vma_mapped_walk(&pvmw)) 1295 goto out_mn; 1296 if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?")) 1297 goto out_unlock; 1298 1299 entry = ptep_get(pvmw.pte); 1300 /* 1301 * Handle PFN swap PTEs, such as device-exclusive ones, that actually 1302 * map pages: give up just like the next folio_walk would. 1303 */ 1304 if (unlikely(!pte_present(entry))) 1305 goto out_unlock; 1306 1307 anon_exclusive = PageAnonExclusive(&folio->page); 1308 if (pte_write(entry) || pte_dirty(entry) || 1309 anon_exclusive || mm_tlb_flush_pending(mm)) { 1310 swapped = folio_test_swapcache(folio); 1311 flush_cache_page(vma, pvmw.address, folio_pfn(folio)); 1312 /* 1313 * Ok this is tricky, when get_user_pages_fast() run it doesn't 1314 * take any lock, therefore the check that we are going to make 1315 * with the pagecount against the mapcount is racy and 1316 * O_DIRECT can happen right after the check. 1317 * So we clear the pte and flush the tlb before the check 1318 * this assure us that no O_DIRECT can happen after the check 1319 * or in the middle of the check. 1320 * 1321 * No need to notify as we are downgrading page table to read 1322 * only not changing it to point to a new page. 1323 * 1324 * See Documentation/mm/mmu_notifier.rst 1325 */ 1326 entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte); 1327 /* 1328 * Check that no O_DIRECT or similar I/O is in progress on the 1329 * page 1330 */ 1331 if (folio_mapcount(folio) + 1 + swapped != folio_ref_count(folio)) { 1332 set_pte_at(mm, pvmw.address, pvmw.pte, entry); 1333 goto out_unlock; 1334 } 1335 1336 /* See folio_try_share_anon_rmap_pte(): clear PTE first. */ 1337 if (anon_exclusive && 1338 folio_try_share_anon_rmap_pte(folio, &folio->page)) { 1339 set_pte_at(mm, pvmw.address, pvmw.pte, entry); 1340 goto out_unlock; 1341 } 1342 1343 if (pte_dirty(entry)) 1344 folio_mark_dirty(folio); 1345 entry = pte_mkclean(entry); 1346 1347 if (pte_write(entry)) 1348 entry = pte_wrprotect(entry); 1349 1350 set_pte_at(mm, pvmw.address, pvmw.pte, entry); 1351 } 1352 *orig_pte = entry; 1353 err = 0; 1354 1355 out_unlock: 1356 page_vma_mapped_walk_done(&pvmw); 1357 out_mn: 1358 mmu_notifier_invalidate_range_end(&range); 1359 out: 1360 return err; 1361 } 1362 1363 /** 1364 * replace_page - replace page in vma by new ksm page 1365 * @vma: vma that holds the pte pointing to page 1366 * @page: the page we are replacing by kpage 1367 * @kpage: the ksm page we replace page by 1368 * @orig_pte: the original value of the pte 1369 * 1370 * Returns 0 on success, -EFAULT on failure. 1371 */ 1372 static int replace_page(struct vm_area_struct *vma, struct page *page, 1373 struct page *kpage, pte_t orig_pte) 1374 { 1375 struct folio *kfolio = page_folio(kpage); 1376 struct mm_struct *mm = vma->vm_mm; 1377 struct folio *folio = page_folio(page); 1378 pmd_t *pmd; 1379 pmd_t pmde; 1380 pte_t *ptep; 1381 pte_t newpte; 1382 spinlock_t *ptl; 1383 unsigned long addr; 1384 int err = -EFAULT; 1385 struct mmu_notifier_range range; 1386 1387 addr = page_address_in_vma(folio, page, vma); 1388 if (addr == -EFAULT) 1389 goto out; 1390 1391 pmd = mm_find_pmd(mm, addr); 1392 if (!pmd) 1393 goto out; 1394 /* 1395 * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at() 1396 * without holding anon_vma lock for write. So when looking for a 1397 * genuine pmde (in which to find pte), test present and !THP together. 1398 */ 1399 pmde = pmdp_get_lockless(pmd); 1400 if (!pmd_present(pmde) || pmd_trans_huge(pmde)) 1401 goto out; 1402 1403 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, addr, 1404 addr + PAGE_SIZE); 1405 mmu_notifier_invalidate_range_start(&range); 1406 1407 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); 1408 if (!ptep) 1409 goto out_mn; 1410 if (!pte_same(ptep_get(ptep), orig_pte)) { 1411 pte_unmap_unlock(ptep, ptl); 1412 goto out_mn; 1413 } 1414 VM_BUG_ON_PAGE(PageAnonExclusive(page), page); 1415 VM_BUG_ON_FOLIO(folio_test_anon(kfolio) && PageAnonExclusive(kpage), 1416 kfolio); 1417 1418 /* 1419 * No need to check ksm_use_zero_pages here: we can only have a 1420 * zero_page here if ksm_use_zero_pages was enabled already. 1421 */ 1422 if (!is_zero_pfn(page_to_pfn(kpage))) { 1423 folio_get(kfolio); 1424 folio_add_anon_rmap_pte(kfolio, kpage, vma, addr, RMAP_NONE); 1425 newpte = mk_pte(kpage, vma->vm_page_prot); 1426 } else { 1427 /* 1428 * Use pte_mkdirty to mark the zero page mapped by KSM, and then 1429 * we can easily track all KSM-placed zero pages by checking if 1430 * the dirty bit in zero page's PTE is set. 1431 */ 1432 newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot))); 1433 ksm_map_zero_page(mm); 1434 /* 1435 * We're replacing an anonymous page with a zero page, which is 1436 * not anonymous. We need to do proper accounting otherwise we 1437 * will get wrong values in /proc, and a BUG message in dmesg 1438 * when tearing down the mm. 1439 */ 1440 dec_mm_counter(mm, MM_ANONPAGES); 1441 } 1442 1443 flush_cache_page(vma, addr, pte_pfn(ptep_get(ptep))); 1444 /* 1445 * No need to notify as we are replacing a read only page with another 1446 * read only page with the same content. 1447 * 1448 * See Documentation/mm/mmu_notifier.rst 1449 */ 1450 ptep_clear_flush(vma, addr, ptep); 1451 set_pte_at(mm, addr, ptep, newpte); 1452 1453 folio_remove_rmap_pte(folio, page, vma); 1454 if (!folio_mapped(folio)) 1455 folio_free_swap(folio); 1456 folio_put(folio); 1457 1458 pte_unmap_unlock(ptep, ptl); 1459 err = 0; 1460 out_mn: 1461 mmu_notifier_invalidate_range_end(&range); 1462 out: 1463 return err; 1464 } 1465 1466 /* 1467 * try_to_merge_one_page - take two pages and merge them into one 1468 * @vma: the vma that holds the pte pointing to page 1469 * @page: the PageAnon page that we want to replace with kpage 1470 * @kpage: the KSM page that we want to map instead of page, 1471 * or NULL the first time when we want to use page as kpage. 1472 * 1473 * This function returns 0 if the pages were merged, -EFAULT otherwise. 1474 */ 1475 static int try_to_merge_one_page(struct vm_area_struct *vma, 1476 struct page *page, struct page *kpage) 1477 { 1478 struct folio *folio = page_folio(page); 1479 pte_t orig_pte = __pte(0); 1480 int err = -EFAULT; 1481 1482 if (page == kpage) /* ksm page forked */ 1483 return 0; 1484 1485 if (!folio_test_anon(folio)) 1486 goto out; 1487 1488 /* 1489 * We need the folio lock to read a stable swapcache flag in 1490 * write_protect_page(). We trylock because we don't want to wait 1491 * here - we prefer to continue scanning and merging different 1492 * pages, then come back to this page when it is unlocked. 1493 */ 1494 if (!folio_trylock(folio)) 1495 goto out; 1496 1497 if (folio_test_large(folio)) { 1498 if (split_huge_page(page)) 1499 goto out_unlock; 1500 folio = page_folio(page); 1501 } 1502 1503 /* 1504 * If this anonymous page is mapped only here, its pte may need 1505 * to be write-protected. If it's mapped elsewhere, all of its 1506 * ptes are necessarily already write-protected. But in either 1507 * case, we need to lock and check page_count is not raised. 1508 */ 1509 if (write_protect_page(vma, folio, &orig_pte) == 0) { 1510 if (!kpage) { 1511 /* 1512 * While we hold folio lock, upgrade folio from 1513 * anon to a NULL stable_node with the KSM flag set: 1514 * stable_tree_insert() will update stable_node. 1515 */ 1516 folio_set_stable_node(folio, NULL); 1517 folio_mark_accessed(folio); 1518 /* 1519 * Page reclaim just frees a clean folio with no dirty 1520 * ptes: make sure that the ksm page would be swapped. 1521 */ 1522 if (!folio_test_dirty(folio)) 1523 folio_mark_dirty(folio); 1524 err = 0; 1525 } else if (pages_identical(page, kpage)) 1526 err = replace_page(vma, page, kpage, orig_pte); 1527 } 1528 1529 out_unlock: 1530 folio_unlock(folio); 1531 out: 1532 return err; 1533 } 1534 1535 /* 1536 * This function returns 0 if the pages were merged or if they are 1537 * no longer merging candidates (e.g., VMA stale), -EFAULT otherwise. 1538 */ 1539 static int try_to_merge_with_zero_page(struct ksm_rmap_item *rmap_item, 1540 struct page *page) 1541 { 1542 struct mm_struct *mm = rmap_item->mm; 1543 int err = -EFAULT; 1544 1545 /* 1546 * Same checksum as an empty page. We attempt to merge it with the 1547 * appropriate zero page if the user enabled this via sysfs. 1548 */ 1549 if (ksm_use_zero_pages && (rmap_item->oldchecksum == zero_checksum)) { 1550 struct vm_area_struct *vma; 1551 1552 mmap_read_lock(mm); 1553 vma = find_mergeable_vma(mm, rmap_item->address); 1554 if (vma) { 1555 err = try_to_merge_one_page(vma, page, 1556 ZERO_PAGE(rmap_item->address)); 1557 trace_ksm_merge_one_page( 1558 page_to_pfn(ZERO_PAGE(rmap_item->address)), 1559 rmap_item, mm, err); 1560 } else { 1561 /* 1562 * If the vma is out of date, we do not need to 1563 * continue. 1564 */ 1565 err = 0; 1566 } 1567 mmap_read_unlock(mm); 1568 } 1569 1570 return err; 1571 } 1572 1573 /* 1574 * try_to_merge_with_ksm_page - like try_to_merge_two_pages, 1575 * but no new kernel page is allocated: kpage must already be a ksm page. 1576 * 1577 * This function returns 0 if the pages were merged, -EFAULT otherwise. 1578 */ 1579 static int try_to_merge_with_ksm_page(struct ksm_rmap_item *rmap_item, 1580 struct page *page, struct page *kpage) 1581 { 1582 struct mm_struct *mm = rmap_item->mm; 1583 struct vm_area_struct *vma; 1584 int err = -EFAULT; 1585 1586 mmap_read_lock(mm); 1587 vma = find_mergeable_vma(mm, rmap_item->address); 1588 if (!vma) 1589 goto out; 1590 1591 err = try_to_merge_one_page(vma, page, kpage); 1592 if (err) 1593 goto out; 1594 1595 /* Unstable nid is in union with stable anon_vma: remove first */ 1596 remove_rmap_item_from_tree(rmap_item); 1597 1598 /* Must get reference to anon_vma while still holding mmap_lock */ 1599 rmap_item->anon_vma = vma->anon_vma; 1600 get_anon_vma(vma->anon_vma); 1601 out: 1602 mmap_read_unlock(mm); 1603 trace_ksm_merge_with_ksm_page(kpage, page_to_pfn(kpage ? kpage : page), 1604 rmap_item, mm, err); 1605 return err; 1606 } 1607 1608 /* 1609 * try_to_merge_two_pages - take two identical pages and prepare them 1610 * to be merged into one page. 1611 * 1612 * This function returns the kpage if we successfully merged two identical 1613 * pages into one ksm page, NULL otherwise. 1614 * 1615 * Note that this function upgrades page to ksm page: if one of the pages 1616 * is already a ksm page, try_to_merge_with_ksm_page should be used. 1617 */ 1618 static struct folio *try_to_merge_two_pages(struct ksm_rmap_item *rmap_item, 1619 struct page *page, 1620 struct ksm_rmap_item *tree_rmap_item, 1621 struct page *tree_page) 1622 { 1623 int err; 1624 1625 err = try_to_merge_with_ksm_page(rmap_item, page, NULL); 1626 if (!err) { 1627 err = try_to_merge_with_ksm_page(tree_rmap_item, 1628 tree_page, page); 1629 /* 1630 * If that fails, we have a ksm page with only one pte 1631 * pointing to it: so break it. 1632 */ 1633 if (err) 1634 break_cow(rmap_item); 1635 } 1636 return err ? NULL : page_folio(page); 1637 } 1638 1639 static __always_inline 1640 bool __is_page_sharing_candidate(struct ksm_stable_node *stable_node, int offset) 1641 { 1642 VM_BUG_ON(stable_node->rmap_hlist_len < 0); 1643 /* 1644 * Check that at least one mapping still exists, otherwise 1645 * there's no much point to merge and share with this 1646 * stable_node, as the underlying tree_page of the other 1647 * sharer is going to be freed soon. 1648 */ 1649 return stable_node->rmap_hlist_len && 1650 stable_node->rmap_hlist_len + offset < ksm_max_page_sharing; 1651 } 1652 1653 static __always_inline 1654 bool is_page_sharing_candidate(struct ksm_stable_node *stable_node) 1655 { 1656 return __is_page_sharing_candidate(stable_node, 0); 1657 } 1658 1659 static struct folio *stable_node_dup(struct ksm_stable_node **_stable_node_dup, 1660 struct ksm_stable_node **_stable_node, 1661 struct rb_root *root, 1662 bool prune_stale_stable_nodes) 1663 { 1664 struct ksm_stable_node *dup, *found = NULL, *stable_node = *_stable_node; 1665 struct hlist_node *hlist_safe; 1666 struct folio *folio, *tree_folio = NULL; 1667 int found_rmap_hlist_len; 1668 1669 if (!prune_stale_stable_nodes || 1670 time_before(jiffies, stable_node->chain_prune_time + 1671 msecs_to_jiffies( 1672 ksm_stable_node_chains_prune_millisecs))) 1673 prune_stale_stable_nodes = false; 1674 else 1675 stable_node->chain_prune_time = jiffies; 1676 1677 hlist_for_each_entry_safe(dup, hlist_safe, 1678 &stable_node->hlist, hlist_dup) { 1679 cond_resched(); 1680 /* 1681 * We must walk all stable_node_dup to prune the stale 1682 * stable nodes during lookup. 1683 * 1684 * ksm_get_folio can drop the nodes from the 1685 * stable_node->hlist if they point to freed pages 1686 * (that's why we do a _safe walk). The "dup" 1687 * stable_node parameter itself will be freed from 1688 * under us if it returns NULL. 1689 */ 1690 folio = ksm_get_folio(dup, KSM_GET_FOLIO_NOLOCK); 1691 if (!folio) 1692 continue; 1693 /* Pick the best candidate if possible. */ 1694 if (!found || (is_page_sharing_candidate(dup) && 1695 (!is_page_sharing_candidate(found) || 1696 dup->rmap_hlist_len > found_rmap_hlist_len))) { 1697 if (found) 1698 folio_put(tree_folio); 1699 found = dup; 1700 found_rmap_hlist_len = found->rmap_hlist_len; 1701 tree_folio = folio; 1702 /* skip put_page for found candidate */ 1703 if (!prune_stale_stable_nodes && 1704 is_page_sharing_candidate(found)) 1705 break; 1706 continue; 1707 } 1708 folio_put(folio); 1709 } 1710 1711 if (found) { 1712 if (hlist_is_singular_node(&found->hlist_dup, &stable_node->hlist)) { 1713 /* 1714 * If there's not just one entry it would 1715 * corrupt memory, better BUG_ON. In KSM 1716 * context with no lock held it's not even 1717 * fatal. 1718 */ 1719 BUG_ON(stable_node->hlist.first->next); 1720 1721 /* 1722 * There's just one entry and it is below the 1723 * deduplication limit so drop the chain. 1724 */ 1725 rb_replace_node(&stable_node->node, &found->node, 1726 root); 1727 free_stable_node(stable_node); 1728 ksm_stable_node_chains--; 1729 ksm_stable_node_dups--; 1730 /* 1731 * NOTE: the caller depends on the stable_node 1732 * to be equal to stable_node_dup if the chain 1733 * was collapsed. 1734 */ 1735 *_stable_node = found; 1736 /* 1737 * Just for robustness, as stable_node is 1738 * otherwise left as a stable pointer, the 1739 * compiler shall optimize it away at build 1740 * time. 1741 */ 1742 stable_node = NULL; 1743 } else if (stable_node->hlist.first != &found->hlist_dup && 1744 __is_page_sharing_candidate(found, 1)) { 1745 /* 1746 * If the found stable_node dup can accept one 1747 * more future merge (in addition to the one 1748 * that is underway) and is not at the head of 1749 * the chain, put it there so next search will 1750 * be quicker in the !prune_stale_stable_nodes 1751 * case. 1752 * 1753 * NOTE: it would be inaccurate to use nr > 1 1754 * instead of checking the hlist.first pointer 1755 * directly, because in the 1756 * prune_stale_stable_nodes case "nr" isn't 1757 * the position of the found dup in the chain, 1758 * but the total number of dups in the chain. 1759 */ 1760 hlist_del(&found->hlist_dup); 1761 hlist_add_head(&found->hlist_dup, 1762 &stable_node->hlist); 1763 } 1764 } else { 1765 /* Its hlist must be empty if no one found. */ 1766 free_stable_node_chain(stable_node, root); 1767 } 1768 1769 *_stable_node_dup = found; 1770 return tree_folio; 1771 } 1772 1773 /* 1774 * Like for ksm_get_folio, this function can free the *_stable_node and 1775 * *_stable_node_dup if the returned tree_page is NULL. 1776 * 1777 * It can also free and overwrite *_stable_node with the found 1778 * stable_node_dup if the chain is collapsed (in which case 1779 * *_stable_node will be equal to *_stable_node_dup like if the chain 1780 * never existed). It's up to the caller to verify tree_page is not 1781 * NULL before dereferencing *_stable_node or *_stable_node_dup. 1782 * 1783 * *_stable_node_dup is really a second output parameter of this 1784 * function and will be overwritten in all cases, the caller doesn't 1785 * need to initialize it. 1786 */ 1787 static struct folio *__stable_node_chain(struct ksm_stable_node **_stable_node_dup, 1788 struct ksm_stable_node **_stable_node, 1789 struct rb_root *root, 1790 bool prune_stale_stable_nodes) 1791 { 1792 struct ksm_stable_node *stable_node = *_stable_node; 1793 1794 if (!is_stable_node_chain(stable_node)) { 1795 *_stable_node_dup = stable_node; 1796 return ksm_get_folio(stable_node, KSM_GET_FOLIO_NOLOCK); 1797 } 1798 return stable_node_dup(_stable_node_dup, _stable_node, root, 1799 prune_stale_stable_nodes); 1800 } 1801 1802 static __always_inline struct folio *chain_prune(struct ksm_stable_node **s_n_d, 1803 struct ksm_stable_node **s_n, 1804 struct rb_root *root) 1805 { 1806 return __stable_node_chain(s_n_d, s_n, root, true); 1807 } 1808 1809 static __always_inline struct folio *chain(struct ksm_stable_node **s_n_d, 1810 struct ksm_stable_node **s_n, 1811 struct rb_root *root) 1812 { 1813 return __stable_node_chain(s_n_d, s_n, root, false); 1814 } 1815 1816 /* 1817 * stable_tree_search - search for page inside the stable tree 1818 * 1819 * This function checks if there is a page inside the stable tree 1820 * with identical content to the page that we are scanning right now. 1821 * 1822 * This function returns the stable tree node of identical content if found, 1823 * -EBUSY if the stable node's page is being migrated, NULL otherwise. 1824 */ 1825 static struct folio *stable_tree_search(struct page *page) 1826 { 1827 int nid; 1828 struct rb_root *root; 1829 struct rb_node **new; 1830 struct rb_node *parent; 1831 struct ksm_stable_node *stable_node, *stable_node_dup; 1832 struct ksm_stable_node *page_node; 1833 struct folio *folio; 1834 1835 folio = page_folio(page); 1836 page_node = folio_stable_node(folio); 1837 if (page_node && page_node->head != &migrate_nodes) { 1838 /* ksm page forked */ 1839 folio_get(folio); 1840 return folio; 1841 } 1842 1843 nid = get_kpfn_nid(folio_pfn(folio)); 1844 root = root_stable_tree + nid; 1845 again: 1846 new = &root->rb_node; 1847 parent = NULL; 1848 1849 while (*new) { 1850 struct folio *tree_folio; 1851 int ret; 1852 1853 cond_resched(); 1854 stable_node = rb_entry(*new, struct ksm_stable_node, node); 1855 tree_folio = chain_prune(&stable_node_dup, &stable_node, root); 1856 if (!tree_folio) { 1857 /* 1858 * If we walked over a stale stable_node, 1859 * ksm_get_folio() will call rb_erase() and it 1860 * may rebalance the tree from under us. So 1861 * restart the search from scratch. Returning 1862 * NULL would be safe too, but we'd generate 1863 * false negative insertions just because some 1864 * stable_node was stale. 1865 */ 1866 goto again; 1867 } 1868 1869 ret = memcmp_pages(page, &tree_folio->page); 1870 folio_put(tree_folio); 1871 1872 parent = *new; 1873 if (ret < 0) 1874 new = &parent->rb_left; 1875 else if (ret > 0) 1876 new = &parent->rb_right; 1877 else { 1878 if (page_node) { 1879 VM_BUG_ON(page_node->head != &migrate_nodes); 1880 /* 1881 * If the mapcount of our migrated KSM folio is 1882 * at most 1, we can merge it with another 1883 * KSM folio where we know that we have space 1884 * for one more mapping without exceeding the 1885 * ksm_max_page_sharing limit: see 1886 * chain_prune(). This way, we can avoid adding 1887 * this stable node to the chain. 1888 */ 1889 if (folio_mapcount(folio) > 1) 1890 goto chain_append; 1891 } 1892 1893 if (!is_page_sharing_candidate(stable_node_dup)) { 1894 /* 1895 * If the stable_node is a chain and 1896 * we got a payload match in memcmp 1897 * but we cannot merge the scanned 1898 * page in any of the existing 1899 * stable_node dups because they're 1900 * all full, we need to wait the 1901 * scanned page to find itself a match 1902 * in the unstable tree to create a 1903 * brand new KSM page to add later to 1904 * the dups of this stable_node. 1905 */ 1906 return NULL; 1907 } 1908 1909 /* 1910 * Lock and unlock the stable_node's page (which 1911 * might already have been migrated) so that page 1912 * migration is sure to notice its raised count. 1913 * It would be more elegant to return stable_node 1914 * than kpage, but that involves more changes. 1915 */ 1916 tree_folio = ksm_get_folio(stable_node_dup, 1917 KSM_GET_FOLIO_TRYLOCK); 1918 1919 if (PTR_ERR(tree_folio) == -EBUSY) 1920 return ERR_PTR(-EBUSY); 1921 1922 if (unlikely(!tree_folio)) 1923 /* 1924 * The tree may have been rebalanced, 1925 * so re-evaluate parent and new. 1926 */ 1927 goto again; 1928 folio_unlock(tree_folio); 1929 1930 if (get_kpfn_nid(stable_node_dup->kpfn) != 1931 NUMA(stable_node_dup->nid)) { 1932 folio_put(tree_folio); 1933 goto replace; 1934 } 1935 return tree_folio; 1936 } 1937 } 1938 1939 if (!page_node) 1940 return NULL; 1941 1942 list_del(&page_node->list); 1943 DO_NUMA(page_node->nid = nid); 1944 rb_link_node(&page_node->node, parent, new); 1945 rb_insert_color(&page_node->node, root); 1946 out: 1947 if (is_page_sharing_candidate(page_node)) { 1948 folio_get(folio); 1949 return folio; 1950 } else 1951 return NULL; 1952 1953 replace: 1954 /* 1955 * If stable_node was a chain and chain_prune collapsed it, 1956 * stable_node has been updated to be the new regular 1957 * stable_node. A collapse of the chain is indistinguishable 1958 * from the case there was no chain in the stable 1959 * rbtree. Otherwise stable_node is the chain and 1960 * stable_node_dup is the dup to replace. 1961 */ 1962 if (stable_node_dup == stable_node) { 1963 VM_BUG_ON(is_stable_node_chain(stable_node_dup)); 1964 VM_BUG_ON(is_stable_node_dup(stable_node_dup)); 1965 /* there is no chain */ 1966 if (page_node) { 1967 VM_BUG_ON(page_node->head != &migrate_nodes); 1968 list_del(&page_node->list); 1969 DO_NUMA(page_node->nid = nid); 1970 rb_replace_node(&stable_node_dup->node, 1971 &page_node->node, 1972 root); 1973 if (is_page_sharing_candidate(page_node)) 1974 folio_get(folio); 1975 else 1976 folio = NULL; 1977 } else { 1978 rb_erase(&stable_node_dup->node, root); 1979 folio = NULL; 1980 } 1981 } else { 1982 VM_BUG_ON(!is_stable_node_chain(stable_node)); 1983 __stable_node_dup_del(stable_node_dup); 1984 if (page_node) { 1985 VM_BUG_ON(page_node->head != &migrate_nodes); 1986 list_del(&page_node->list); 1987 DO_NUMA(page_node->nid = nid); 1988 stable_node_chain_add_dup(page_node, stable_node); 1989 if (is_page_sharing_candidate(page_node)) 1990 folio_get(folio); 1991 else 1992 folio = NULL; 1993 } else { 1994 folio = NULL; 1995 } 1996 } 1997 stable_node_dup->head = &migrate_nodes; 1998 list_add(&stable_node_dup->list, stable_node_dup->head); 1999 return folio; 2000 2001 chain_append: 2002 /* 2003 * If stable_node was a chain and chain_prune collapsed it, 2004 * stable_node has been updated to be the new regular 2005 * stable_node. A collapse of the chain is indistinguishable 2006 * from the case there was no chain in the stable 2007 * rbtree. Otherwise stable_node is the chain and 2008 * stable_node_dup is the dup to replace. 2009 */ 2010 if (stable_node_dup == stable_node) { 2011 VM_BUG_ON(is_stable_node_dup(stable_node_dup)); 2012 /* chain is missing so create it */ 2013 stable_node = alloc_stable_node_chain(stable_node_dup, 2014 root); 2015 if (!stable_node) 2016 return NULL; 2017 } 2018 /* 2019 * Add this stable_node dup that was 2020 * migrated to the stable_node chain 2021 * of the current nid for this page 2022 * content. 2023 */ 2024 VM_BUG_ON(!is_stable_node_dup(stable_node_dup)); 2025 VM_BUG_ON(page_node->head != &migrate_nodes); 2026 list_del(&page_node->list); 2027 DO_NUMA(page_node->nid = nid); 2028 stable_node_chain_add_dup(page_node, stable_node); 2029 goto out; 2030 } 2031 2032 /* 2033 * stable_tree_insert - insert stable tree node pointing to new ksm page 2034 * into the stable tree. 2035 * 2036 * This function returns the stable tree node just allocated on success, 2037 * NULL otherwise. 2038 */ 2039 static struct ksm_stable_node *stable_tree_insert(struct folio *kfolio) 2040 { 2041 int nid; 2042 unsigned long kpfn; 2043 struct rb_root *root; 2044 struct rb_node **new; 2045 struct rb_node *parent; 2046 struct ksm_stable_node *stable_node, *stable_node_dup; 2047 bool need_chain = false; 2048 2049 kpfn = folio_pfn(kfolio); 2050 nid = get_kpfn_nid(kpfn); 2051 root = root_stable_tree + nid; 2052 again: 2053 parent = NULL; 2054 new = &root->rb_node; 2055 2056 while (*new) { 2057 struct folio *tree_folio; 2058 int ret; 2059 2060 cond_resched(); 2061 stable_node = rb_entry(*new, struct ksm_stable_node, node); 2062 tree_folio = chain(&stable_node_dup, &stable_node, root); 2063 if (!tree_folio) { 2064 /* 2065 * If we walked over a stale stable_node, 2066 * ksm_get_folio() will call rb_erase() and it 2067 * may rebalance the tree from under us. So 2068 * restart the search from scratch. Returning 2069 * NULL would be safe too, but we'd generate 2070 * false negative insertions just because some 2071 * stable_node was stale. 2072 */ 2073 goto again; 2074 } 2075 2076 ret = memcmp_pages(&kfolio->page, &tree_folio->page); 2077 folio_put(tree_folio); 2078 2079 parent = *new; 2080 if (ret < 0) 2081 new = &parent->rb_left; 2082 else if (ret > 0) 2083 new = &parent->rb_right; 2084 else { 2085 need_chain = true; 2086 break; 2087 } 2088 } 2089 2090 stable_node_dup = alloc_stable_node(); 2091 if (!stable_node_dup) 2092 return NULL; 2093 2094 INIT_HLIST_HEAD(&stable_node_dup->hlist); 2095 stable_node_dup->kpfn = kpfn; 2096 stable_node_dup->rmap_hlist_len = 0; 2097 DO_NUMA(stable_node_dup->nid = nid); 2098 if (!need_chain) { 2099 rb_link_node(&stable_node_dup->node, parent, new); 2100 rb_insert_color(&stable_node_dup->node, root); 2101 } else { 2102 if (!is_stable_node_chain(stable_node)) { 2103 struct ksm_stable_node *orig = stable_node; 2104 /* chain is missing so create it */ 2105 stable_node = alloc_stable_node_chain(orig, root); 2106 if (!stable_node) { 2107 free_stable_node(stable_node_dup); 2108 return NULL; 2109 } 2110 } 2111 stable_node_chain_add_dup(stable_node_dup, stable_node); 2112 } 2113 2114 folio_set_stable_node(kfolio, stable_node_dup); 2115 2116 return stable_node_dup; 2117 } 2118 2119 /* 2120 * unstable_tree_search_insert - search for identical page, 2121 * else insert rmap_item into the unstable tree. 2122 * 2123 * This function searches for a page in the unstable tree identical to the 2124 * page currently being scanned; and if no identical page is found in the 2125 * tree, we insert rmap_item as a new object into the unstable tree. 2126 * 2127 * This function returns pointer to rmap_item found to be identical 2128 * to the currently scanned page, NULL otherwise. 2129 * 2130 * This function does both searching and inserting, because they share 2131 * the same walking algorithm in an rbtree. 2132 */ 2133 static 2134 struct ksm_rmap_item *unstable_tree_search_insert(struct ksm_rmap_item *rmap_item, 2135 struct page *page, 2136 struct page **tree_pagep) 2137 { 2138 struct rb_node **new; 2139 struct rb_root *root; 2140 struct rb_node *parent = NULL; 2141 int nid; 2142 2143 nid = get_kpfn_nid(page_to_pfn(page)); 2144 root = root_unstable_tree + nid; 2145 new = &root->rb_node; 2146 2147 while (*new) { 2148 struct ksm_rmap_item *tree_rmap_item; 2149 struct page *tree_page; 2150 int ret; 2151 2152 cond_resched(); 2153 tree_rmap_item = rb_entry(*new, struct ksm_rmap_item, node); 2154 tree_page = get_mergeable_page(tree_rmap_item); 2155 if (!tree_page) 2156 return NULL; 2157 2158 /* 2159 * Don't substitute a ksm page for a forked page. 2160 */ 2161 if (page == tree_page) { 2162 put_page(tree_page); 2163 return NULL; 2164 } 2165 2166 ret = memcmp_pages(page, tree_page); 2167 2168 parent = *new; 2169 if (ret < 0) { 2170 put_page(tree_page); 2171 new = &parent->rb_left; 2172 } else if (ret > 0) { 2173 put_page(tree_page); 2174 new = &parent->rb_right; 2175 } else if (!ksm_merge_across_nodes && 2176 page_to_nid(tree_page) != nid) { 2177 /* 2178 * If tree_page has been migrated to another NUMA node, 2179 * it will be flushed out and put in the right unstable 2180 * tree next time: only merge with it when across_nodes. 2181 */ 2182 put_page(tree_page); 2183 return NULL; 2184 } else { 2185 *tree_pagep = tree_page; 2186 return tree_rmap_item; 2187 } 2188 } 2189 2190 rmap_item->address |= UNSTABLE_FLAG; 2191 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); 2192 DO_NUMA(rmap_item->nid = nid); 2193 rb_link_node(&rmap_item->node, parent, new); 2194 rb_insert_color(&rmap_item->node, root); 2195 2196 ksm_pages_unshared++; 2197 return NULL; 2198 } 2199 2200 /* 2201 * stable_tree_append - add another rmap_item to the linked list of 2202 * rmap_items hanging off a given node of the stable tree, all sharing 2203 * the same ksm page. 2204 */ 2205 static void stable_tree_append(struct ksm_rmap_item *rmap_item, 2206 struct ksm_stable_node *stable_node, 2207 bool max_page_sharing_bypass) 2208 { 2209 /* 2210 * rmap won't find this mapping if we don't insert the 2211 * rmap_item in the right stable_node 2212 * duplicate. page_migration could break later if rmap breaks, 2213 * so we can as well crash here. We really need to check for 2214 * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check 2215 * for other negative values as an underflow if detected here 2216 * for the first time (and not when decreasing rmap_hlist_len) 2217 * would be sign of memory corruption in the stable_node. 2218 */ 2219 BUG_ON(stable_node->rmap_hlist_len < 0); 2220 2221 stable_node->rmap_hlist_len++; 2222 if (!max_page_sharing_bypass) 2223 /* possibly non fatal but unexpected overflow, only warn */ 2224 WARN_ON_ONCE(stable_node->rmap_hlist_len > 2225 ksm_max_page_sharing); 2226 2227 rmap_item->head = stable_node; 2228 rmap_item->address |= STABLE_FLAG; 2229 hlist_add_head(&rmap_item->hlist, &stable_node->hlist); 2230 2231 if (rmap_item->hlist.next) 2232 ksm_pages_sharing++; 2233 else 2234 ksm_pages_shared++; 2235 2236 rmap_item->mm->ksm_merging_pages++; 2237 } 2238 2239 /* 2240 * cmp_and_merge_page - first see if page can be merged into the stable tree; 2241 * if not, compare checksum to previous and if it's the same, see if page can 2242 * be inserted into the unstable tree, or merged with a page already there and 2243 * both transferred to the stable tree. 2244 * 2245 * @page: the page that we are searching identical page to. 2246 * @rmap_item: the reverse mapping into the virtual address of this page 2247 */ 2248 static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_item) 2249 { 2250 struct folio *folio = page_folio(page); 2251 struct ksm_rmap_item *tree_rmap_item; 2252 struct page *tree_page = NULL; 2253 struct ksm_stable_node *stable_node; 2254 struct folio *kfolio; 2255 unsigned int checksum; 2256 int err; 2257 bool max_page_sharing_bypass = false; 2258 2259 stable_node = folio_stable_node(folio); 2260 if (stable_node) { 2261 if (stable_node->head != &migrate_nodes && 2262 get_kpfn_nid(READ_ONCE(stable_node->kpfn)) != 2263 NUMA(stable_node->nid)) { 2264 stable_node_dup_del(stable_node); 2265 stable_node->head = &migrate_nodes; 2266 list_add(&stable_node->list, stable_node->head); 2267 } 2268 if (stable_node->head != &migrate_nodes && 2269 rmap_item->head == stable_node) 2270 return; 2271 /* 2272 * If it's a KSM fork, allow it to go over the sharing limit 2273 * without warnings. 2274 */ 2275 if (!is_page_sharing_candidate(stable_node)) 2276 max_page_sharing_bypass = true; 2277 } else { 2278 remove_rmap_item_from_tree(rmap_item); 2279 2280 /* 2281 * If the hash value of the page has changed from the last time 2282 * we calculated it, this page is changing frequently: therefore we 2283 * don't want to insert it in the unstable tree, and we don't want 2284 * to waste our time searching for something identical to it there. 2285 */ 2286 checksum = calc_checksum(page); 2287 if (rmap_item->oldchecksum != checksum) { 2288 rmap_item->oldchecksum = checksum; 2289 return; 2290 } 2291 2292 if (!try_to_merge_with_zero_page(rmap_item, page)) 2293 return; 2294 } 2295 2296 /* Start by searching for the folio in the stable tree */ 2297 kfolio = stable_tree_search(page); 2298 if (kfolio == folio && rmap_item->head == stable_node) { 2299 folio_put(kfolio); 2300 return; 2301 } 2302 2303 remove_rmap_item_from_tree(rmap_item); 2304 2305 if (kfolio) { 2306 if (kfolio == ERR_PTR(-EBUSY)) 2307 return; 2308 2309 err = try_to_merge_with_ksm_page(rmap_item, page, &kfolio->page); 2310 if (!err) { 2311 /* 2312 * The page was successfully merged: 2313 * add its rmap_item to the stable tree. 2314 */ 2315 folio_lock(kfolio); 2316 stable_tree_append(rmap_item, folio_stable_node(kfolio), 2317 max_page_sharing_bypass); 2318 folio_unlock(kfolio); 2319 } 2320 folio_put(kfolio); 2321 return; 2322 } 2323 2324 tree_rmap_item = 2325 unstable_tree_search_insert(rmap_item, page, &tree_page); 2326 if (tree_rmap_item) { 2327 bool split; 2328 2329 kfolio = try_to_merge_two_pages(rmap_item, page, 2330 tree_rmap_item, tree_page); 2331 /* 2332 * If both pages we tried to merge belong to the same compound 2333 * page, then we actually ended up increasing the reference 2334 * count of the same compound page twice, and split_huge_page 2335 * failed. 2336 * Here we set a flag if that happened, and we use it later to 2337 * try split_huge_page again. Since we call put_page right 2338 * afterwards, the reference count will be correct and 2339 * split_huge_page should succeed. 2340 */ 2341 split = PageTransCompound(page) 2342 && compound_head(page) == compound_head(tree_page); 2343 put_page(tree_page); 2344 if (kfolio) { 2345 /* 2346 * The pages were successfully merged: insert new 2347 * node in the stable tree and add both rmap_items. 2348 */ 2349 folio_lock(kfolio); 2350 stable_node = stable_tree_insert(kfolio); 2351 if (stable_node) { 2352 stable_tree_append(tree_rmap_item, stable_node, 2353 false); 2354 stable_tree_append(rmap_item, stable_node, 2355 false); 2356 } 2357 folio_unlock(kfolio); 2358 2359 /* 2360 * If we fail to insert the page into the stable tree, 2361 * we will have 2 virtual addresses that are pointing 2362 * to a ksm page left outside the stable tree, 2363 * in which case we need to break_cow on both. 2364 */ 2365 if (!stable_node) { 2366 break_cow(tree_rmap_item); 2367 break_cow(rmap_item); 2368 } 2369 } else if (split) { 2370 /* 2371 * We are here if we tried to merge two pages and 2372 * failed because they both belonged to the same 2373 * compound page. We will split the page now, but no 2374 * merging will take place. 2375 * We do not want to add the cost of a full lock; if 2376 * the page is locked, it is better to skip it and 2377 * perhaps try again later. 2378 */ 2379 if (!folio_trylock(folio)) 2380 return; 2381 split_huge_page(page); 2382 folio = page_folio(page); 2383 folio_unlock(folio); 2384 } 2385 } 2386 } 2387 2388 static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot, 2389 struct ksm_rmap_item **rmap_list, 2390 unsigned long addr) 2391 { 2392 struct ksm_rmap_item *rmap_item; 2393 2394 while (*rmap_list) { 2395 rmap_item = *rmap_list; 2396 if ((rmap_item->address & PAGE_MASK) == addr) 2397 return rmap_item; 2398 if (rmap_item->address > addr) 2399 break; 2400 *rmap_list = rmap_item->rmap_list; 2401 remove_rmap_item_from_tree(rmap_item); 2402 free_rmap_item(rmap_item); 2403 } 2404 2405 rmap_item = alloc_rmap_item(); 2406 if (rmap_item) { 2407 /* It has already been zeroed */ 2408 rmap_item->mm = mm_slot->slot.mm; 2409 rmap_item->mm->ksm_rmap_items++; 2410 rmap_item->address = addr; 2411 rmap_item->rmap_list = *rmap_list; 2412 *rmap_list = rmap_item; 2413 } 2414 return rmap_item; 2415 } 2416 2417 /* 2418 * Calculate skip age for the ksm page age. The age determines how often 2419 * de-duplicating has already been tried unsuccessfully. If the age is 2420 * smaller, the scanning of this page is skipped for less scans. 2421 * 2422 * @age: rmap_item age of page 2423 */ 2424 static unsigned int skip_age(rmap_age_t age) 2425 { 2426 if (age <= 3) 2427 return 1; 2428 if (age <= 5) 2429 return 2; 2430 if (age <= 8) 2431 return 4; 2432 2433 return 8; 2434 } 2435 2436 /* 2437 * Determines if a page should be skipped for the current scan. 2438 * 2439 * @folio: folio containing the page to check 2440 * @rmap_item: associated rmap_item of page 2441 */ 2442 static bool should_skip_rmap_item(struct folio *folio, 2443 struct ksm_rmap_item *rmap_item) 2444 { 2445 rmap_age_t age; 2446 2447 if (!ksm_smart_scan) 2448 return false; 2449 2450 /* 2451 * Never skip pages that are already KSM; pages cmp_and_merge_page() 2452 * will essentially ignore them, but we still have to process them 2453 * properly. 2454 */ 2455 if (folio_test_ksm(folio)) 2456 return false; 2457 2458 age = rmap_item->age; 2459 if (age != U8_MAX) 2460 rmap_item->age++; 2461 2462 /* 2463 * Smaller ages are not skipped, they need to get a chance to go 2464 * through the different phases of the KSM merging. 2465 */ 2466 if (age < 3) 2467 return false; 2468 2469 /* 2470 * Are we still allowed to skip? If not, then don't skip it 2471 * and determine how much more often we are allowed to skip next. 2472 */ 2473 if (!rmap_item->remaining_skips) { 2474 rmap_item->remaining_skips = skip_age(age); 2475 return false; 2476 } 2477 2478 /* Skip this page */ 2479 ksm_pages_skipped++; 2480 rmap_item->remaining_skips--; 2481 remove_rmap_item_from_tree(rmap_item); 2482 return true; 2483 } 2484 2485 struct ksm_next_page_arg { 2486 struct folio *folio; 2487 struct page *page; 2488 unsigned long addr; 2489 }; 2490 2491 static int ksm_next_page_pmd_entry(pmd_t *pmdp, unsigned long addr, unsigned long end, 2492 struct mm_walk *walk) 2493 { 2494 struct ksm_next_page_arg *private = walk->private; 2495 struct vm_area_struct *vma = walk->vma; 2496 pte_t *start_ptep = NULL, *ptep, pte; 2497 struct mm_struct *mm = walk->mm; 2498 struct folio *folio; 2499 struct page *page; 2500 spinlock_t *ptl; 2501 pmd_t pmd; 2502 2503 if (ksm_test_exit(mm)) 2504 return 0; 2505 2506 cond_resched(); 2507 2508 pmd = pmdp_get_lockless(pmdp); 2509 if (!pmd_present(pmd)) 2510 return 0; 2511 2512 if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && pmd_leaf(pmd)) { 2513 ptl = pmd_lock(mm, pmdp); 2514 pmd = pmdp_get(pmdp); 2515 2516 if (!pmd_present(pmd)) { 2517 goto not_found_unlock; 2518 } else if (pmd_leaf(pmd)) { 2519 page = vm_normal_page_pmd(vma, addr, pmd); 2520 if (!page) 2521 goto not_found_unlock; 2522 folio = page_folio(page); 2523 2524 if (folio_is_zone_device(folio) || !folio_test_anon(folio)) 2525 goto not_found_unlock; 2526 2527 page += ((addr & (PMD_SIZE - 1)) >> PAGE_SHIFT); 2528 goto found_unlock; 2529 } 2530 spin_unlock(ptl); 2531 } 2532 2533 start_ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); 2534 if (!start_ptep) 2535 return 0; 2536 2537 for (ptep = start_ptep; addr < end; ptep++, addr += PAGE_SIZE) { 2538 pte = ptep_get(ptep); 2539 2540 if (!pte_present(pte)) 2541 continue; 2542 2543 page = vm_normal_page(vma, addr, pte); 2544 if (!page) 2545 continue; 2546 folio = page_folio(page); 2547 2548 if (folio_is_zone_device(folio) || !folio_test_anon(folio)) 2549 continue; 2550 goto found_unlock; 2551 } 2552 2553 not_found_unlock: 2554 spin_unlock(ptl); 2555 if (start_ptep) 2556 pte_unmap(start_ptep); 2557 return 0; 2558 found_unlock: 2559 folio_get(folio); 2560 spin_unlock(ptl); 2561 if (start_ptep) 2562 pte_unmap(start_ptep); 2563 private->page = page; 2564 private->folio = folio; 2565 private->addr = addr; 2566 return 1; 2567 } 2568 2569 static struct mm_walk_ops ksm_next_page_ops = { 2570 .pmd_entry = ksm_next_page_pmd_entry, 2571 .walk_lock = PGWALK_RDLOCK, 2572 }; 2573 2574 static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) 2575 { 2576 struct mm_struct *mm; 2577 struct ksm_mm_slot *mm_slot; 2578 struct mm_slot *slot; 2579 struct vm_area_struct *vma; 2580 struct ksm_rmap_item *rmap_item; 2581 struct vma_iterator vmi; 2582 int nid; 2583 2584 if (list_empty(&ksm_mm_head.slot.mm_node)) 2585 return NULL; 2586 2587 mm_slot = ksm_scan.mm_slot; 2588 if (mm_slot == &ksm_mm_head) { 2589 advisor_start_scan(); 2590 trace_ksm_start_scan(ksm_scan.seqnr, ksm_rmap_items); 2591 2592 /* 2593 * A number of pages can hang around indefinitely in per-cpu 2594 * LRU cache, raised page count preventing write_protect_page 2595 * from merging them. Though it doesn't really matter much, 2596 * it is puzzling to see some stuck in pages_volatile until 2597 * other activity jostles them out, and they also prevented 2598 * LTP's KSM test from succeeding deterministically; so drain 2599 * them here (here rather than on entry to ksm_do_scan(), 2600 * so we don't IPI too often when pages_to_scan is set low). 2601 */ 2602 lru_add_drain_all(); 2603 2604 /* 2605 * Whereas stale stable_nodes on the stable_tree itself 2606 * get pruned in the regular course of stable_tree_search(), 2607 * those moved out to the migrate_nodes list can accumulate: 2608 * so prune them once before each full scan. 2609 */ 2610 if (!ksm_merge_across_nodes) { 2611 struct ksm_stable_node *stable_node, *next; 2612 struct folio *folio; 2613 2614 list_for_each_entry_safe(stable_node, next, 2615 &migrate_nodes, list) { 2616 folio = ksm_get_folio(stable_node, 2617 KSM_GET_FOLIO_NOLOCK); 2618 if (folio) 2619 folio_put(folio); 2620 cond_resched(); 2621 } 2622 } 2623 2624 for (nid = 0; nid < ksm_nr_node_ids; nid++) 2625 root_unstable_tree[nid] = RB_ROOT; 2626 2627 spin_lock(&ksm_mmlist_lock); 2628 slot = list_entry(mm_slot->slot.mm_node.next, 2629 struct mm_slot, mm_node); 2630 mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); 2631 ksm_scan.mm_slot = mm_slot; 2632 spin_unlock(&ksm_mmlist_lock); 2633 /* 2634 * Although we tested list_empty() above, a racing __ksm_exit 2635 * of the last mm on the list may have removed it since then. 2636 */ 2637 if (mm_slot == &ksm_mm_head) 2638 return NULL; 2639 next_mm: 2640 ksm_scan.address = 0; 2641 ksm_scan.rmap_list = &mm_slot->rmap_list; 2642 } 2643 2644 slot = &mm_slot->slot; 2645 mm = slot->mm; 2646 vma_iter_init(&vmi, mm, ksm_scan.address); 2647 2648 mmap_read_lock(mm); 2649 if (ksm_test_exit(mm)) 2650 goto no_vmas; 2651 2652 for_each_vma(vmi, vma) { 2653 if (!(vma->vm_flags & VM_MERGEABLE)) 2654 continue; 2655 if (ksm_scan.address < vma->vm_start) 2656 ksm_scan.address = vma->vm_start; 2657 if (!vma->anon_vma) 2658 ksm_scan.address = vma->vm_end; 2659 2660 while (ksm_scan.address < vma->vm_end) { 2661 struct ksm_next_page_arg ksm_next_page_arg; 2662 struct page *tmp_page = NULL; 2663 struct folio *folio; 2664 2665 if (ksm_test_exit(mm)) 2666 break; 2667 2668 int found; 2669 2670 found = walk_page_range_vma(vma, ksm_scan.address, 2671 vma->vm_end, 2672 &ksm_next_page_ops, 2673 &ksm_next_page_arg); 2674 2675 if (found > 0) { 2676 folio = ksm_next_page_arg.folio; 2677 tmp_page = ksm_next_page_arg.page; 2678 ksm_scan.address = ksm_next_page_arg.addr; 2679 } else { 2680 VM_WARN_ON_ONCE(found < 0); 2681 ksm_scan.address = vma->vm_end - PAGE_SIZE; 2682 } 2683 2684 if (tmp_page) { 2685 flush_anon_page(vma, tmp_page, ksm_scan.address); 2686 flush_dcache_page(tmp_page); 2687 rmap_item = get_next_rmap_item(mm_slot, 2688 ksm_scan.rmap_list, ksm_scan.address); 2689 if (rmap_item) { 2690 ksm_scan.rmap_list = 2691 &rmap_item->rmap_list; 2692 2693 if (should_skip_rmap_item(folio, rmap_item)) { 2694 folio_put(folio); 2695 goto next_page; 2696 } 2697 2698 ksm_scan.address += PAGE_SIZE; 2699 *page = tmp_page; 2700 } else { 2701 folio_put(folio); 2702 } 2703 mmap_read_unlock(mm); 2704 return rmap_item; 2705 } 2706 next_page: 2707 ksm_scan.address += PAGE_SIZE; 2708 cond_resched(); 2709 } 2710 } 2711 2712 if (ksm_test_exit(mm)) { 2713 no_vmas: 2714 ksm_scan.address = 0; 2715 ksm_scan.rmap_list = &mm_slot->rmap_list; 2716 } 2717 /* 2718 * Nuke all the rmap_items that are above this current rmap: 2719 * because there were no VM_MERGEABLE vmas with such addresses. 2720 */ 2721 remove_trailing_rmap_items(ksm_scan.rmap_list); 2722 2723 spin_lock(&ksm_mmlist_lock); 2724 slot = list_entry(mm_slot->slot.mm_node.next, 2725 struct mm_slot, mm_node); 2726 ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); 2727 if (ksm_scan.address == 0) { 2728 /* 2729 * We've completed a full scan of all vmas, holding mmap_lock 2730 * throughout, and found no VM_MERGEABLE: so do the same as 2731 * __ksm_exit does to remove this mm from all our lists now. 2732 * This applies either when cleaning up after __ksm_exit 2733 * (but beware: we can reach here even before __ksm_exit), 2734 * or when all VM_MERGEABLE areas have been unmapped (and 2735 * mmap_lock then protects against race with MADV_MERGEABLE). 2736 */ 2737 hash_del(&mm_slot->slot.hash); 2738 list_del(&mm_slot->slot.mm_node); 2739 spin_unlock(&ksm_mmlist_lock); 2740 2741 mm_slot_free(mm_slot_cache, mm_slot); 2742 /* 2743 * Only clear MMF_VM_MERGEABLE. We must not clear 2744 * MMF_VM_MERGE_ANY, because for those MMF_VM_MERGE_ANY process, 2745 * perhaps their mm_struct has just been added to ksm_mm_slot 2746 * list, and its process has not yet officially started running 2747 * or has not yet performed mmap/brk to allocate anonymous VMAS. 2748 */ 2749 mm_flags_clear(MMF_VM_MERGEABLE, mm); 2750 mmap_read_unlock(mm); 2751 mmdrop(mm); 2752 } else { 2753 mmap_read_unlock(mm); 2754 /* 2755 * mmap_read_unlock(mm) first because after 2756 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may 2757 * already have been freed under us by __ksm_exit() 2758 * because the "mm_slot" is still hashed and 2759 * ksm_scan.mm_slot doesn't point to it anymore. 2760 */ 2761 spin_unlock(&ksm_mmlist_lock); 2762 } 2763 2764 /* Repeat until we've completed scanning the whole list */ 2765 mm_slot = ksm_scan.mm_slot; 2766 if (mm_slot != &ksm_mm_head) 2767 goto next_mm; 2768 2769 advisor_stop_scan(); 2770 2771 trace_ksm_stop_scan(ksm_scan.seqnr, ksm_rmap_items); 2772 ksm_scan.seqnr++; 2773 return NULL; 2774 } 2775 2776 /** 2777 * ksm_do_scan - the ksm scanner main worker function. 2778 * @scan_npages: number of pages we want to scan before we return. 2779 */ 2780 static void ksm_do_scan(unsigned int scan_npages) 2781 { 2782 struct ksm_rmap_item *rmap_item; 2783 struct page *page; 2784 2785 while (scan_npages-- && likely(!freezing(current))) { 2786 cond_resched(); 2787 rmap_item = scan_get_next_rmap_item(&page); 2788 if (!rmap_item) 2789 return; 2790 cmp_and_merge_page(page, rmap_item); 2791 put_page(page); 2792 ksm_pages_scanned++; 2793 } 2794 } 2795 2796 static int ksmd_should_run(void) 2797 { 2798 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.slot.mm_node); 2799 } 2800 2801 static int ksm_scan_thread(void *nothing) 2802 { 2803 unsigned int sleep_ms; 2804 2805 set_freezable(); 2806 set_user_nice(current, 5); 2807 2808 while (!kthread_should_stop()) { 2809 mutex_lock(&ksm_thread_mutex); 2810 wait_while_offlining(); 2811 if (ksmd_should_run()) 2812 ksm_do_scan(ksm_thread_pages_to_scan); 2813 mutex_unlock(&ksm_thread_mutex); 2814 2815 if (ksmd_should_run()) { 2816 sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs); 2817 wait_event_freezable_timeout(ksm_iter_wait, 2818 sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs), 2819 msecs_to_jiffies(sleep_ms)); 2820 } else { 2821 wait_event_freezable(ksm_thread_wait, 2822 ksmd_should_run() || kthread_should_stop()); 2823 } 2824 } 2825 return 0; 2826 } 2827 2828 static bool __ksm_should_add_vma(const struct file *file, vm_flags_t vm_flags) 2829 { 2830 if (vm_flags & VM_MERGEABLE) 2831 return false; 2832 2833 return ksm_compatible(file, vm_flags); 2834 } 2835 2836 static void __ksm_add_vma(struct vm_area_struct *vma) 2837 { 2838 if (__ksm_should_add_vma(vma->vm_file, vma->vm_flags)) 2839 vm_flags_set(vma, VM_MERGEABLE); 2840 } 2841 2842 static int __ksm_del_vma(struct vm_area_struct *vma) 2843 { 2844 int err; 2845 2846 if (!(vma->vm_flags & VM_MERGEABLE)) 2847 return 0; 2848 2849 if (vma->anon_vma) { 2850 err = break_ksm(vma, vma->vm_start, vma->vm_end, true); 2851 if (err) 2852 return err; 2853 } 2854 2855 vm_flags_clear(vma, VM_MERGEABLE); 2856 return 0; 2857 } 2858 /** 2859 * ksm_vma_flags - Update VMA flags to mark as mergeable if compatible 2860 * 2861 * @mm: Proposed VMA's mm_struct 2862 * @file: Proposed VMA's file-backed mapping, if any. 2863 * @vm_flags: Proposed VMA"s flags. 2864 * 2865 * Returns: @vm_flags possibly updated to mark mergeable. 2866 */ 2867 vm_flags_t ksm_vma_flags(struct mm_struct *mm, const struct file *file, 2868 vm_flags_t vm_flags) 2869 { 2870 if (mm_flags_test(MMF_VM_MERGE_ANY, mm) && 2871 __ksm_should_add_vma(file, vm_flags)) { 2872 vm_flags |= VM_MERGEABLE; 2873 /* 2874 * Generally, the flags here always include MMF_VM_MERGEABLE. 2875 * However, in rare cases, this flag may be cleared by ksmd who 2876 * scans a cycle without finding any mergeable vma. 2877 */ 2878 if (unlikely(!mm_flags_test(MMF_VM_MERGEABLE, mm))) 2879 __ksm_enter(mm); 2880 } 2881 2882 return vm_flags; 2883 } 2884 2885 static void ksm_add_vmas(struct mm_struct *mm) 2886 { 2887 struct vm_area_struct *vma; 2888 2889 VMA_ITERATOR(vmi, mm, 0); 2890 for_each_vma(vmi, vma) 2891 __ksm_add_vma(vma); 2892 } 2893 2894 static int ksm_del_vmas(struct mm_struct *mm) 2895 { 2896 struct vm_area_struct *vma; 2897 int err; 2898 2899 VMA_ITERATOR(vmi, mm, 0); 2900 for_each_vma(vmi, vma) { 2901 err = __ksm_del_vma(vma); 2902 if (err) 2903 return err; 2904 } 2905 return 0; 2906 } 2907 2908 /** 2909 * ksm_enable_merge_any - Add mm to mm ksm list and enable merging on all 2910 * compatible VMA's 2911 * 2912 * @mm: Pointer to mm 2913 * 2914 * Returns 0 on success, otherwise error code 2915 */ 2916 int ksm_enable_merge_any(struct mm_struct *mm) 2917 { 2918 int err; 2919 2920 if (mm_flags_test(MMF_VM_MERGE_ANY, mm)) 2921 return 0; 2922 2923 if (!mm_flags_test(MMF_VM_MERGEABLE, mm)) { 2924 err = __ksm_enter(mm); 2925 if (err) 2926 return err; 2927 } 2928 2929 mm_flags_set(MMF_VM_MERGE_ANY, mm); 2930 ksm_add_vmas(mm); 2931 2932 return 0; 2933 } 2934 2935 /** 2936 * ksm_disable_merge_any - Disable merging on all compatible VMA's of the mm, 2937 * previously enabled via ksm_enable_merge_any(). 2938 * 2939 * Disabling merging implies unmerging any merged pages, like setting 2940 * MADV_UNMERGEABLE would. If unmerging fails, the whole operation fails and 2941 * merging on all compatible VMA's remains enabled. 2942 * 2943 * @mm: Pointer to mm 2944 * 2945 * Returns 0 on success, otherwise error code 2946 */ 2947 int ksm_disable_merge_any(struct mm_struct *mm) 2948 { 2949 int err; 2950 2951 if (!mm_flags_test(MMF_VM_MERGE_ANY, mm)) 2952 return 0; 2953 2954 err = ksm_del_vmas(mm); 2955 if (err) { 2956 ksm_add_vmas(mm); 2957 return err; 2958 } 2959 2960 mm_flags_clear(MMF_VM_MERGE_ANY, mm); 2961 return 0; 2962 } 2963 2964 int ksm_disable(struct mm_struct *mm) 2965 { 2966 mmap_assert_write_locked(mm); 2967 2968 if (!mm_flags_test(MMF_VM_MERGEABLE, mm)) 2969 return 0; 2970 if (mm_flags_test(MMF_VM_MERGE_ANY, mm)) 2971 return ksm_disable_merge_any(mm); 2972 return ksm_del_vmas(mm); 2973 } 2974 2975 int ksm_madvise(struct vm_area_struct *vma, unsigned long start, 2976 unsigned long end, int advice, vm_flags_t *vm_flags) 2977 { 2978 struct mm_struct *mm = vma->vm_mm; 2979 int err; 2980 2981 switch (advice) { 2982 case MADV_MERGEABLE: 2983 if (vma->vm_flags & VM_MERGEABLE) 2984 return 0; 2985 if (!vma_ksm_compatible(vma)) 2986 return 0; 2987 2988 if (!mm_flags_test(MMF_VM_MERGEABLE, mm)) { 2989 err = __ksm_enter(mm); 2990 if (err) 2991 return err; 2992 } 2993 2994 *vm_flags |= VM_MERGEABLE; 2995 break; 2996 2997 case MADV_UNMERGEABLE: 2998 if (!(*vm_flags & VM_MERGEABLE)) 2999 return 0; /* just ignore the advice */ 3000 3001 if (vma->anon_vma) { 3002 err = break_ksm(vma, start, end, true); 3003 if (err) 3004 return err; 3005 } 3006 3007 *vm_flags &= ~VM_MERGEABLE; 3008 break; 3009 } 3010 3011 return 0; 3012 } 3013 EXPORT_SYMBOL_GPL(ksm_madvise); 3014 3015 int __ksm_enter(struct mm_struct *mm) 3016 { 3017 struct ksm_mm_slot *mm_slot; 3018 struct mm_slot *slot; 3019 int needs_wakeup; 3020 3021 mm_slot = mm_slot_alloc(mm_slot_cache); 3022 if (!mm_slot) 3023 return -ENOMEM; 3024 3025 slot = &mm_slot->slot; 3026 3027 /* Check ksm_run too? Would need tighter locking */ 3028 needs_wakeup = list_empty(&ksm_mm_head.slot.mm_node); 3029 3030 spin_lock(&ksm_mmlist_lock); 3031 mm_slot_insert(mm_slots_hash, mm, slot); 3032 /* 3033 * When KSM_RUN_MERGE (or KSM_RUN_STOP), 3034 * insert just behind the scanning cursor, to let the area settle 3035 * down a little; when fork is followed by immediate exec, we don't 3036 * want ksmd to waste time setting up and tearing down an rmap_list. 3037 * 3038 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its 3039 * scanning cursor, otherwise KSM pages in newly forked mms will be 3040 * missed: then we might as well insert at the end of the list. 3041 */ 3042 if (ksm_run & KSM_RUN_UNMERGE) 3043 list_add_tail(&slot->mm_node, &ksm_mm_head.slot.mm_node); 3044 else 3045 list_add_tail(&slot->mm_node, &ksm_scan.mm_slot->slot.mm_node); 3046 spin_unlock(&ksm_mmlist_lock); 3047 3048 mm_flags_set(MMF_VM_MERGEABLE, mm); 3049 mmgrab(mm); 3050 3051 if (needs_wakeup) 3052 wake_up_interruptible(&ksm_thread_wait); 3053 3054 trace_ksm_enter(mm); 3055 return 0; 3056 } 3057 3058 void __ksm_exit(struct mm_struct *mm) 3059 { 3060 struct ksm_mm_slot *mm_slot = NULL; 3061 struct mm_slot *slot; 3062 int easy_to_free = 0; 3063 3064 /* 3065 * This process is exiting: if it's straightforward (as is the 3066 * case when ksmd was never running), free mm_slot immediately. 3067 * But if it's at the cursor or has rmap_items linked to it, use 3068 * mmap_lock to synchronize with any break_cows before pagetables 3069 * are freed, and leave the mm_slot on the list for ksmd to free. 3070 * Beware: ksm may already have noticed it exiting and freed the slot. 3071 */ 3072 3073 spin_lock(&ksm_mmlist_lock); 3074 slot = mm_slot_lookup(mm_slots_hash, mm); 3075 if (!slot) 3076 goto unlock; 3077 mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); 3078 if (ksm_scan.mm_slot == mm_slot) 3079 goto unlock; 3080 if (!mm_slot->rmap_list) { 3081 hash_del(&slot->hash); 3082 list_del(&slot->mm_node); 3083 easy_to_free = 1; 3084 } else { 3085 list_move(&slot->mm_node, 3086 &ksm_scan.mm_slot->slot.mm_node); 3087 } 3088 unlock: 3089 spin_unlock(&ksm_mmlist_lock); 3090 3091 if (easy_to_free) { 3092 mm_slot_free(mm_slot_cache, mm_slot); 3093 mm_flags_clear(MMF_VM_MERGE_ANY, mm); 3094 mm_flags_clear(MMF_VM_MERGEABLE, mm); 3095 mmdrop(mm); 3096 } else if (mm_slot) { 3097 mmap_write_lock(mm); 3098 mmap_write_unlock(mm); 3099 } 3100 3101 trace_ksm_exit(mm); 3102 } 3103 3104 struct folio *ksm_might_need_to_copy(struct folio *folio, 3105 struct vm_area_struct *vma, unsigned long addr) 3106 { 3107 struct page *page = folio_page(folio, 0); 3108 struct anon_vma *anon_vma = folio_anon_vma(folio); 3109 struct folio *new_folio; 3110 3111 if (folio_test_large(folio)) 3112 return folio; 3113 3114 if (folio_test_ksm(folio)) { 3115 if (folio_stable_node(folio) && 3116 !(ksm_run & KSM_RUN_UNMERGE)) 3117 return folio; /* no need to copy it */ 3118 } else if (!anon_vma) { 3119 return folio; /* no need to copy it */ 3120 } else if (folio->index == linear_page_index(vma, addr) && 3121 anon_vma->root == vma->anon_vma->root) { 3122 return folio; /* still no need to copy it */ 3123 } 3124 if (PageHWPoison(page)) 3125 return ERR_PTR(-EHWPOISON); 3126 if (!folio_test_uptodate(folio)) 3127 return folio; /* let do_swap_page report the error */ 3128 3129 new_folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, addr); 3130 if (new_folio && 3131 mem_cgroup_charge(new_folio, vma->vm_mm, GFP_KERNEL)) { 3132 folio_put(new_folio); 3133 new_folio = NULL; 3134 } 3135 if (new_folio) { 3136 if (copy_mc_user_highpage(folio_page(new_folio, 0), page, 3137 addr, vma)) { 3138 folio_put(new_folio); 3139 return ERR_PTR(-EHWPOISON); 3140 } 3141 folio_set_dirty(new_folio); 3142 __folio_mark_uptodate(new_folio); 3143 __folio_set_locked(new_folio); 3144 #ifdef CONFIG_SWAP 3145 count_vm_event(KSM_SWPIN_COPY); 3146 #endif 3147 } 3148 3149 return new_folio; 3150 } 3151 3152 void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc) 3153 { 3154 struct ksm_stable_node *stable_node; 3155 struct ksm_rmap_item *rmap_item; 3156 int search_new_forks = 0; 3157 3158 VM_BUG_ON_FOLIO(!folio_test_ksm(folio), folio); 3159 3160 /* 3161 * Rely on the page lock to protect against concurrent modifications 3162 * to that page's node of the stable tree. 3163 */ 3164 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); 3165 3166 stable_node = folio_stable_node(folio); 3167 if (!stable_node) 3168 return; 3169 again: 3170 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { 3171 struct anon_vma *anon_vma = rmap_item->anon_vma; 3172 struct anon_vma_chain *vmac; 3173 struct vm_area_struct *vma; 3174 3175 cond_resched(); 3176 if (!anon_vma_trylock_read(anon_vma)) { 3177 if (rwc->try_lock) { 3178 rwc->contended = true; 3179 return; 3180 } 3181 anon_vma_lock_read(anon_vma); 3182 } 3183 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, 3184 0, ULONG_MAX) { 3185 unsigned long addr; 3186 3187 cond_resched(); 3188 vma = vmac->vma; 3189 3190 /* Ignore the stable/unstable/sqnr flags */ 3191 addr = rmap_item->address & PAGE_MASK; 3192 3193 if (addr < vma->vm_start || addr >= vma->vm_end) 3194 continue; 3195 /* 3196 * Initially we examine only the vma which covers this 3197 * rmap_item; but later, if there is still work to do, 3198 * we examine covering vmas in other mms: in case they 3199 * were forked from the original since ksmd passed. 3200 */ 3201 if ((rmap_item->mm == vma->vm_mm) == search_new_forks) 3202 continue; 3203 3204 if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg)) 3205 continue; 3206 3207 if (!rwc->rmap_one(folio, vma, addr, rwc->arg)) { 3208 anon_vma_unlock_read(anon_vma); 3209 return; 3210 } 3211 if (rwc->done && rwc->done(folio)) { 3212 anon_vma_unlock_read(anon_vma); 3213 return; 3214 } 3215 } 3216 anon_vma_unlock_read(anon_vma); 3217 } 3218 if (!search_new_forks++) 3219 goto again; 3220 } 3221 3222 #ifdef CONFIG_MEMORY_FAILURE 3223 /* 3224 * Collect processes when the error hit an ksm page. 3225 */ 3226 void collect_procs_ksm(const struct folio *folio, const struct page *page, 3227 struct list_head *to_kill, int force_early) 3228 { 3229 struct ksm_stable_node *stable_node; 3230 struct ksm_rmap_item *rmap_item; 3231 struct vm_area_struct *vma; 3232 struct task_struct *tsk; 3233 3234 stable_node = folio_stable_node(folio); 3235 if (!stable_node) 3236 return; 3237 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { 3238 struct anon_vma *av = rmap_item->anon_vma; 3239 3240 anon_vma_lock_read(av); 3241 rcu_read_lock(); 3242 for_each_process(tsk) { 3243 struct anon_vma_chain *vmac; 3244 unsigned long addr; 3245 struct task_struct *t = 3246 task_early_kill(tsk, force_early); 3247 if (!t) 3248 continue; 3249 anon_vma_interval_tree_foreach(vmac, &av->rb_root, 0, 3250 ULONG_MAX) 3251 { 3252 vma = vmac->vma; 3253 if (vma->vm_mm == t->mm) { 3254 addr = rmap_item->address & PAGE_MASK; 3255 add_to_kill_ksm(t, page, vma, to_kill, 3256 addr); 3257 } 3258 } 3259 } 3260 rcu_read_unlock(); 3261 anon_vma_unlock_read(av); 3262 } 3263 } 3264 #endif 3265 3266 #ifdef CONFIG_MIGRATION 3267 void folio_migrate_ksm(struct folio *newfolio, struct folio *folio) 3268 { 3269 struct ksm_stable_node *stable_node; 3270 3271 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); 3272 VM_BUG_ON_FOLIO(!folio_test_locked(newfolio), newfolio); 3273 VM_BUG_ON_FOLIO(newfolio->mapping != folio->mapping, newfolio); 3274 3275 stable_node = folio_stable_node(folio); 3276 if (stable_node) { 3277 VM_BUG_ON_FOLIO(stable_node->kpfn != folio_pfn(folio), folio); 3278 stable_node->kpfn = folio_pfn(newfolio); 3279 /* 3280 * newfolio->mapping was set in advance; now we need smp_wmb() 3281 * to make sure that the new stable_node->kpfn is visible 3282 * to ksm_get_folio() before it can see that folio->mapping 3283 * has gone stale (or that the swapcache flag has been cleared). 3284 */ 3285 smp_wmb(); 3286 folio_set_stable_node(folio, NULL); 3287 } 3288 } 3289 #endif /* CONFIG_MIGRATION */ 3290 3291 #ifdef CONFIG_MEMORY_HOTREMOVE 3292 static void wait_while_offlining(void) 3293 { 3294 while (ksm_run & KSM_RUN_OFFLINE) { 3295 mutex_unlock(&ksm_thread_mutex); 3296 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE), 3297 TASK_UNINTERRUPTIBLE); 3298 mutex_lock(&ksm_thread_mutex); 3299 } 3300 } 3301 3302 static bool stable_node_dup_remove_range(struct ksm_stable_node *stable_node, 3303 unsigned long start_pfn, 3304 unsigned long end_pfn) 3305 { 3306 if (stable_node->kpfn >= start_pfn && 3307 stable_node->kpfn < end_pfn) { 3308 /* 3309 * Don't ksm_get_folio, page has already gone: 3310 * which is why we keep kpfn instead of page* 3311 */ 3312 remove_node_from_stable_tree(stable_node); 3313 return true; 3314 } 3315 return false; 3316 } 3317 3318 static bool stable_node_chain_remove_range(struct ksm_stable_node *stable_node, 3319 unsigned long start_pfn, 3320 unsigned long end_pfn, 3321 struct rb_root *root) 3322 { 3323 struct ksm_stable_node *dup; 3324 struct hlist_node *hlist_safe; 3325 3326 if (!is_stable_node_chain(stable_node)) { 3327 VM_BUG_ON(is_stable_node_dup(stable_node)); 3328 return stable_node_dup_remove_range(stable_node, start_pfn, 3329 end_pfn); 3330 } 3331 3332 hlist_for_each_entry_safe(dup, hlist_safe, 3333 &stable_node->hlist, hlist_dup) { 3334 VM_BUG_ON(!is_stable_node_dup(dup)); 3335 stable_node_dup_remove_range(dup, start_pfn, end_pfn); 3336 } 3337 if (hlist_empty(&stable_node->hlist)) { 3338 free_stable_node_chain(stable_node, root); 3339 return true; /* notify caller that tree was rebalanced */ 3340 } else 3341 return false; 3342 } 3343 3344 static void ksm_check_stable_tree(unsigned long start_pfn, 3345 unsigned long end_pfn) 3346 { 3347 struct ksm_stable_node *stable_node, *next; 3348 struct rb_node *node; 3349 int nid; 3350 3351 for (nid = 0; nid < ksm_nr_node_ids; nid++) { 3352 node = rb_first(root_stable_tree + nid); 3353 while (node) { 3354 stable_node = rb_entry(node, struct ksm_stable_node, node); 3355 if (stable_node_chain_remove_range(stable_node, 3356 start_pfn, end_pfn, 3357 root_stable_tree + 3358 nid)) 3359 node = rb_first(root_stable_tree + nid); 3360 else 3361 node = rb_next(node); 3362 cond_resched(); 3363 } 3364 } 3365 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) { 3366 if (stable_node->kpfn >= start_pfn && 3367 stable_node->kpfn < end_pfn) 3368 remove_node_from_stable_tree(stable_node); 3369 cond_resched(); 3370 } 3371 } 3372 3373 static int ksm_memory_callback(struct notifier_block *self, 3374 unsigned long action, void *arg) 3375 { 3376 struct memory_notify *mn = arg; 3377 3378 switch (action) { 3379 case MEM_GOING_OFFLINE: 3380 /* 3381 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items() 3382 * and remove_all_stable_nodes() while memory is going offline: 3383 * it is unsafe for them to touch the stable tree at this time. 3384 * But break_ksm(), rmap lookups and other entry points 3385 * which do not need the ksm_thread_mutex are all safe. 3386 */ 3387 mutex_lock(&ksm_thread_mutex); 3388 ksm_run |= KSM_RUN_OFFLINE; 3389 mutex_unlock(&ksm_thread_mutex); 3390 break; 3391 3392 case MEM_OFFLINE: 3393 /* 3394 * Most of the work is done by page migration; but there might 3395 * be a few stable_nodes left over, still pointing to struct 3396 * pages which have been offlined: prune those from the tree, 3397 * otherwise ksm_get_folio() might later try to access a 3398 * non-existent struct page. 3399 */ 3400 ksm_check_stable_tree(mn->start_pfn, 3401 mn->start_pfn + mn->nr_pages); 3402 fallthrough; 3403 case MEM_CANCEL_OFFLINE: 3404 mutex_lock(&ksm_thread_mutex); 3405 ksm_run &= ~KSM_RUN_OFFLINE; 3406 mutex_unlock(&ksm_thread_mutex); 3407 3408 smp_mb(); /* wake_up_bit advises this */ 3409 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE)); 3410 break; 3411 } 3412 return NOTIFY_OK; 3413 } 3414 #else 3415 static void wait_while_offlining(void) 3416 { 3417 } 3418 #endif /* CONFIG_MEMORY_HOTREMOVE */ 3419 3420 #ifdef CONFIG_PROC_FS 3421 /* 3422 * The process is mergeable only if any VMA is currently 3423 * applicable to KSM. 3424 * 3425 * The mmap lock must be held in read mode. 3426 */ 3427 bool ksm_process_mergeable(struct mm_struct *mm) 3428 { 3429 struct vm_area_struct *vma; 3430 3431 mmap_assert_locked(mm); 3432 VMA_ITERATOR(vmi, mm, 0); 3433 for_each_vma(vmi, vma) 3434 if (vma->vm_flags & VM_MERGEABLE) 3435 return true; 3436 3437 return false; 3438 } 3439 3440 long ksm_process_profit(struct mm_struct *mm) 3441 { 3442 return (long)(mm->ksm_merging_pages + mm_ksm_zero_pages(mm)) * PAGE_SIZE - 3443 mm->ksm_rmap_items * sizeof(struct ksm_rmap_item); 3444 } 3445 #endif /* CONFIG_PROC_FS */ 3446 3447 #ifdef CONFIG_SYSFS 3448 /* 3449 * This all compiles without CONFIG_SYSFS, but is a waste of space. 3450 */ 3451 3452 #define KSM_ATTR_RO(_name) \ 3453 static struct kobj_attribute _name##_attr = __ATTR_RO(_name) 3454 #define KSM_ATTR(_name) \ 3455 static struct kobj_attribute _name##_attr = __ATTR_RW(_name) 3456 3457 static ssize_t sleep_millisecs_show(struct kobject *kobj, 3458 struct kobj_attribute *attr, char *buf) 3459 { 3460 return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs); 3461 } 3462 3463 static ssize_t sleep_millisecs_store(struct kobject *kobj, 3464 struct kobj_attribute *attr, 3465 const char *buf, size_t count) 3466 { 3467 unsigned int msecs; 3468 int err; 3469 3470 err = kstrtouint(buf, 10, &msecs); 3471 if (err) 3472 return -EINVAL; 3473 3474 ksm_thread_sleep_millisecs = msecs; 3475 wake_up_interruptible(&ksm_iter_wait); 3476 3477 return count; 3478 } 3479 KSM_ATTR(sleep_millisecs); 3480 3481 static ssize_t pages_to_scan_show(struct kobject *kobj, 3482 struct kobj_attribute *attr, char *buf) 3483 { 3484 return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan); 3485 } 3486 3487 static ssize_t pages_to_scan_store(struct kobject *kobj, 3488 struct kobj_attribute *attr, 3489 const char *buf, size_t count) 3490 { 3491 unsigned int nr_pages; 3492 int err; 3493 3494 if (ksm_advisor != KSM_ADVISOR_NONE) 3495 return -EINVAL; 3496 3497 err = kstrtouint(buf, 10, &nr_pages); 3498 if (err) 3499 return -EINVAL; 3500 3501 ksm_thread_pages_to_scan = nr_pages; 3502 3503 return count; 3504 } 3505 KSM_ATTR(pages_to_scan); 3506 3507 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, 3508 char *buf) 3509 { 3510 return sysfs_emit(buf, "%lu\n", ksm_run); 3511 } 3512 3513 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, 3514 const char *buf, size_t count) 3515 { 3516 unsigned int flags; 3517 int err; 3518 3519 err = kstrtouint(buf, 10, &flags); 3520 if (err) 3521 return -EINVAL; 3522 if (flags > KSM_RUN_UNMERGE) 3523 return -EINVAL; 3524 3525 /* 3526 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. 3527 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, 3528 * breaking COW to free the pages_shared (but leaves mm_slots 3529 * on the list for when ksmd may be set running again). 3530 */ 3531 3532 mutex_lock(&ksm_thread_mutex); 3533 wait_while_offlining(); 3534 if (ksm_run != flags) { 3535 ksm_run = flags; 3536 if (flags & KSM_RUN_UNMERGE) { 3537 set_current_oom_origin(); 3538 err = unmerge_and_remove_all_rmap_items(); 3539 clear_current_oom_origin(); 3540 if (err) { 3541 ksm_run = KSM_RUN_STOP; 3542 count = err; 3543 } 3544 } 3545 } 3546 mutex_unlock(&ksm_thread_mutex); 3547 3548 if (flags & KSM_RUN_MERGE) 3549 wake_up_interruptible(&ksm_thread_wait); 3550 3551 return count; 3552 } 3553 KSM_ATTR(run); 3554 3555 #ifdef CONFIG_NUMA 3556 static ssize_t merge_across_nodes_show(struct kobject *kobj, 3557 struct kobj_attribute *attr, char *buf) 3558 { 3559 return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes); 3560 } 3561 3562 static ssize_t merge_across_nodes_store(struct kobject *kobj, 3563 struct kobj_attribute *attr, 3564 const char *buf, size_t count) 3565 { 3566 int err; 3567 unsigned long knob; 3568 3569 err = kstrtoul(buf, 10, &knob); 3570 if (err) 3571 return err; 3572 if (knob > 1) 3573 return -EINVAL; 3574 3575 mutex_lock(&ksm_thread_mutex); 3576 wait_while_offlining(); 3577 if (ksm_merge_across_nodes != knob) { 3578 if (ksm_pages_shared || remove_all_stable_nodes()) 3579 err = -EBUSY; 3580 else if (root_stable_tree == one_stable_tree) { 3581 struct rb_root *buf; 3582 /* 3583 * This is the first time that we switch away from the 3584 * default of merging across nodes: must now allocate 3585 * a buffer to hold as many roots as may be needed. 3586 * Allocate stable and unstable together: 3587 * MAXSMP NODES_SHIFT 10 will use 16kB. 3588 */ 3589 buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf), 3590 GFP_KERNEL); 3591 /* Let us assume that RB_ROOT is NULL is zero */ 3592 if (!buf) 3593 err = -ENOMEM; 3594 else { 3595 root_stable_tree = buf; 3596 root_unstable_tree = buf + nr_node_ids; 3597 /* Stable tree is empty but not the unstable */ 3598 root_unstable_tree[0] = one_unstable_tree[0]; 3599 } 3600 } 3601 if (!err) { 3602 ksm_merge_across_nodes = knob; 3603 ksm_nr_node_ids = knob ? 1 : nr_node_ids; 3604 } 3605 } 3606 mutex_unlock(&ksm_thread_mutex); 3607 3608 return err ? err : count; 3609 } 3610 KSM_ATTR(merge_across_nodes); 3611 #endif 3612 3613 static ssize_t use_zero_pages_show(struct kobject *kobj, 3614 struct kobj_attribute *attr, char *buf) 3615 { 3616 return sysfs_emit(buf, "%u\n", ksm_use_zero_pages); 3617 } 3618 static ssize_t use_zero_pages_store(struct kobject *kobj, 3619 struct kobj_attribute *attr, 3620 const char *buf, size_t count) 3621 { 3622 int err; 3623 bool value; 3624 3625 err = kstrtobool(buf, &value); 3626 if (err) 3627 return -EINVAL; 3628 3629 ksm_use_zero_pages = value; 3630 3631 return count; 3632 } 3633 KSM_ATTR(use_zero_pages); 3634 3635 static ssize_t max_page_sharing_show(struct kobject *kobj, 3636 struct kobj_attribute *attr, char *buf) 3637 { 3638 return sysfs_emit(buf, "%u\n", ksm_max_page_sharing); 3639 } 3640 3641 static ssize_t max_page_sharing_store(struct kobject *kobj, 3642 struct kobj_attribute *attr, 3643 const char *buf, size_t count) 3644 { 3645 int err; 3646 int knob; 3647 3648 err = kstrtoint(buf, 10, &knob); 3649 if (err) 3650 return err; 3651 /* 3652 * When a KSM page is created it is shared by 2 mappings. This 3653 * being a signed comparison, it implicitly verifies it's not 3654 * negative. 3655 */ 3656 if (knob < 2) 3657 return -EINVAL; 3658 3659 if (READ_ONCE(ksm_max_page_sharing) == knob) 3660 return count; 3661 3662 mutex_lock(&ksm_thread_mutex); 3663 wait_while_offlining(); 3664 if (ksm_max_page_sharing != knob) { 3665 if (ksm_pages_shared || remove_all_stable_nodes()) 3666 err = -EBUSY; 3667 else 3668 ksm_max_page_sharing = knob; 3669 } 3670 mutex_unlock(&ksm_thread_mutex); 3671 3672 return err ? err : count; 3673 } 3674 KSM_ATTR(max_page_sharing); 3675 3676 static ssize_t pages_scanned_show(struct kobject *kobj, 3677 struct kobj_attribute *attr, char *buf) 3678 { 3679 return sysfs_emit(buf, "%lu\n", ksm_pages_scanned); 3680 } 3681 KSM_ATTR_RO(pages_scanned); 3682 3683 static ssize_t pages_shared_show(struct kobject *kobj, 3684 struct kobj_attribute *attr, char *buf) 3685 { 3686 return sysfs_emit(buf, "%lu\n", ksm_pages_shared); 3687 } 3688 KSM_ATTR_RO(pages_shared); 3689 3690 static ssize_t pages_sharing_show(struct kobject *kobj, 3691 struct kobj_attribute *attr, char *buf) 3692 { 3693 return sysfs_emit(buf, "%lu\n", ksm_pages_sharing); 3694 } 3695 KSM_ATTR_RO(pages_sharing); 3696 3697 static ssize_t pages_unshared_show(struct kobject *kobj, 3698 struct kobj_attribute *attr, char *buf) 3699 { 3700 return sysfs_emit(buf, "%lu\n", ksm_pages_unshared); 3701 } 3702 KSM_ATTR_RO(pages_unshared); 3703 3704 static ssize_t pages_volatile_show(struct kobject *kobj, 3705 struct kobj_attribute *attr, char *buf) 3706 { 3707 long ksm_pages_volatile; 3708 3709 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared 3710 - ksm_pages_sharing - ksm_pages_unshared; 3711 /* 3712 * It was not worth any locking to calculate that statistic, 3713 * but it might therefore sometimes be negative: conceal that. 3714 */ 3715 if (ksm_pages_volatile < 0) 3716 ksm_pages_volatile = 0; 3717 return sysfs_emit(buf, "%ld\n", ksm_pages_volatile); 3718 } 3719 KSM_ATTR_RO(pages_volatile); 3720 3721 static ssize_t pages_skipped_show(struct kobject *kobj, 3722 struct kobj_attribute *attr, char *buf) 3723 { 3724 return sysfs_emit(buf, "%lu\n", ksm_pages_skipped); 3725 } 3726 KSM_ATTR_RO(pages_skipped); 3727 3728 static ssize_t ksm_zero_pages_show(struct kobject *kobj, 3729 struct kobj_attribute *attr, char *buf) 3730 { 3731 return sysfs_emit(buf, "%ld\n", atomic_long_read(&ksm_zero_pages)); 3732 } 3733 KSM_ATTR_RO(ksm_zero_pages); 3734 3735 static ssize_t general_profit_show(struct kobject *kobj, 3736 struct kobj_attribute *attr, char *buf) 3737 { 3738 long general_profit; 3739 3740 general_profit = (ksm_pages_sharing + atomic_long_read(&ksm_zero_pages)) * PAGE_SIZE - 3741 ksm_rmap_items * sizeof(struct ksm_rmap_item); 3742 3743 return sysfs_emit(buf, "%ld\n", general_profit); 3744 } 3745 KSM_ATTR_RO(general_profit); 3746 3747 static ssize_t stable_node_dups_show(struct kobject *kobj, 3748 struct kobj_attribute *attr, char *buf) 3749 { 3750 return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups); 3751 } 3752 KSM_ATTR_RO(stable_node_dups); 3753 3754 static ssize_t stable_node_chains_show(struct kobject *kobj, 3755 struct kobj_attribute *attr, char *buf) 3756 { 3757 return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains); 3758 } 3759 KSM_ATTR_RO(stable_node_chains); 3760 3761 static ssize_t 3762 stable_node_chains_prune_millisecs_show(struct kobject *kobj, 3763 struct kobj_attribute *attr, 3764 char *buf) 3765 { 3766 return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs); 3767 } 3768 3769 static ssize_t 3770 stable_node_chains_prune_millisecs_store(struct kobject *kobj, 3771 struct kobj_attribute *attr, 3772 const char *buf, size_t count) 3773 { 3774 unsigned int msecs; 3775 int err; 3776 3777 err = kstrtouint(buf, 10, &msecs); 3778 if (err) 3779 return -EINVAL; 3780 3781 ksm_stable_node_chains_prune_millisecs = msecs; 3782 3783 return count; 3784 } 3785 KSM_ATTR(stable_node_chains_prune_millisecs); 3786 3787 static ssize_t full_scans_show(struct kobject *kobj, 3788 struct kobj_attribute *attr, char *buf) 3789 { 3790 return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr); 3791 } 3792 KSM_ATTR_RO(full_scans); 3793 3794 static ssize_t smart_scan_show(struct kobject *kobj, 3795 struct kobj_attribute *attr, char *buf) 3796 { 3797 return sysfs_emit(buf, "%u\n", ksm_smart_scan); 3798 } 3799 3800 static ssize_t smart_scan_store(struct kobject *kobj, 3801 struct kobj_attribute *attr, 3802 const char *buf, size_t count) 3803 { 3804 int err; 3805 bool value; 3806 3807 err = kstrtobool(buf, &value); 3808 if (err) 3809 return -EINVAL; 3810 3811 ksm_smart_scan = value; 3812 return count; 3813 } 3814 KSM_ATTR(smart_scan); 3815 3816 static ssize_t advisor_mode_show(struct kobject *kobj, 3817 struct kobj_attribute *attr, char *buf) 3818 { 3819 const char *output; 3820 3821 if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) 3822 output = "none [scan-time]"; 3823 else 3824 output = "[none] scan-time"; 3825 3826 return sysfs_emit(buf, "%s\n", output); 3827 } 3828 3829 static ssize_t advisor_mode_store(struct kobject *kobj, 3830 struct kobj_attribute *attr, const char *buf, 3831 size_t count) 3832 { 3833 enum ksm_advisor_type curr_advisor = ksm_advisor; 3834 3835 if (sysfs_streq("scan-time", buf)) 3836 ksm_advisor = KSM_ADVISOR_SCAN_TIME; 3837 else if (sysfs_streq("none", buf)) 3838 ksm_advisor = KSM_ADVISOR_NONE; 3839 else 3840 return -EINVAL; 3841 3842 /* Set advisor default values */ 3843 if (curr_advisor != ksm_advisor) 3844 set_advisor_defaults(); 3845 3846 return count; 3847 } 3848 KSM_ATTR(advisor_mode); 3849 3850 static ssize_t advisor_max_cpu_show(struct kobject *kobj, 3851 struct kobj_attribute *attr, char *buf) 3852 { 3853 return sysfs_emit(buf, "%u\n", ksm_advisor_max_cpu); 3854 } 3855 3856 static ssize_t advisor_max_cpu_store(struct kobject *kobj, 3857 struct kobj_attribute *attr, 3858 const char *buf, size_t count) 3859 { 3860 int err; 3861 unsigned long value; 3862 3863 err = kstrtoul(buf, 10, &value); 3864 if (err) 3865 return -EINVAL; 3866 3867 ksm_advisor_max_cpu = value; 3868 return count; 3869 } 3870 KSM_ATTR(advisor_max_cpu); 3871 3872 static ssize_t advisor_min_pages_to_scan_show(struct kobject *kobj, 3873 struct kobj_attribute *attr, char *buf) 3874 { 3875 return sysfs_emit(buf, "%lu\n", ksm_advisor_min_pages_to_scan); 3876 } 3877 3878 static ssize_t advisor_min_pages_to_scan_store(struct kobject *kobj, 3879 struct kobj_attribute *attr, 3880 const char *buf, size_t count) 3881 { 3882 int err; 3883 unsigned long value; 3884 3885 err = kstrtoul(buf, 10, &value); 3886 if (err) 3887 return -EINVAL; 3888 3889 ksm_advisor_min_pages_to_scan = value; 3890 return count; 3891 } 3892 KSM_ATTR(advisor_min_pages_to_scan); 3893 3894 static ssize_t advisor_max_pages_to_scan_show(struct kobject *kobj, 3895 struct kobj_attribute *attr, char *buf) 3896 { 3897 return sysfs_emit(buf, "%lu\n", ksm_advisor_max_pages_to_scan); 3898 } 3899 3900 static ssize_t advisor_max_pages_to_scan_store(struct kobject *kobj, 3901 struct kobj_attribute *attr, 3902 const char *buf, size_t count) 3903 { 3904 int err; 3905 unsigned long value; 3906 3907 err = kstrtoul(buf, 10, &value); 3908 if (err) 3909 return -EINVAL; 3910 3911 ksm_advisor_max_pages_to_scan = value; 3912 return count; 3913 } 3914 KSM_ATTR(advisor_max_pages_to_scan); 3915 3916 static ssize_t advisor_target_scan_time_show(struct kobject *kobj, 3917 struct kobj_attribute *attr, char *buf) 3918 { 3919 return sysfs_emit(buf, "%lu\n", ksm_advisor_target_scan_time); 3920 } 3921 3922 static ssize_t advisor_target_scan_time_store(struct kobject *kobj, 3923 struct kobj_attribute *attr, 3924 const char *buf, size_t count) 3925 { 3926 int err; 3927 unsigned long value; 3928 3929 err = kstrtoul(buf, 10, &value); 3930 if (err) 3931 return -EINVAL; 3932 if (value < 1) 3933 return -EINVAL; 3934 3935 ksm_advisor_target_scan_time = value; 3936 return count; 3937 } 3938 KSM_ATTR(advisor_target_scan_time); 3939 3940 static struct attribute *ksm_attrs[] = { 3941 &sleep_millisecs_attr.attr, 3942 &pages_to_scan_attr.attr, 3943 &run_attr.attr, 3944 &pages_scanned_attr.attr, 3945 &pages_shared_attr.attr, 3946 &pages_sharing_attr.attr, 3947 &pages_unshared_attr.attr, 3948 &pages_volatile_attr.attr, 3949 &pages_skipped_attr.attr, 3950 &ksm_zero_pages_attr.attr, 3951 &full_scans_attr.attr, 3952 #ifdef CONFIG_NUMA 3953 &merge_across_nodes_attr.attr, 3954 #endif 3955 &max_page_sharing_attr.attr, 3956 &stable_node_chains_attr.attr, 3957 &stable_node_dups_attr.attr, 3958 &stable_node_chains_prune_millisecs_attr.attr, 3959 &use_zero_pages_attr.attr, 3960 &general_profit_attr.attr, 3961 &smart_scan_attr.attr, 3962 &advisor_mode_attr.attr, 3963 &advisor_max_cpu_attr.attr, 3964 &advisor_min_pages_to_scan_attr.attr, 3965 &advisor_max_pages_to_scan_attr.attr, 3966 &advisor_target_scan_time_attr.attr, 3967 NULL, 3968 }; 3969 3970 static const struct attribute_group ksm_attr_group = { 3971 .attrs = ksm_attrs, 3972 .name = "ksm", 3973 }; 3974 #endif /* CONFIG_SYSFS */ 3975 3976 static int __init ksm_init(void) 3977 { 3978 struct task_struct *ksm_thread; 3979 int err; 3980 3981 /* The correct value depends on page size and endianness */ 3982 zero_checksum = calc_checksum(ZERO_PAGE(0)); 3983 /* Default to false for backwards compatibility */ 3984 ksm_use_zero_pages = false; 3985 3986 err = ksm_slab_init(); 3987 if (err) 3988 goto out; 3989 3990 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); 3991 if (IS_ERR(ksm_thread)) { 3992 pr_err("ksm: creating kthread failed\n"); 3993 err = PTR_ERR(ksm_thread); 3994 goto out_free; 3995 } 3996 3997 #ifdef CONFIG_SYSFS 3998 err = sysfs_create_group(mm_kobj, &ksm_attr_group); 3999 if (err) { 4000 pr_err("ksm: register sysfs failed\n"); 4001 kthread_stop(ksm_thread); 4002 goto out_free; 4003 } 4004 #else 4005 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */ 4006 4007 #endif /* CONFIG_SYSFS */ 4008 4009 #ifdef CONFIG_MEMORY_HOTREMOVE 4010 /* There is no significance to this priority 100 */ 4011 hotplug_memory_notifier(ksm_memory_callback, KSM_CALLBACK_PRI); 4012 #endif 4013 return 0; 4014 4015 out_free: 4016 ksm_slab_free(); 4017 out: 4018 return err; 4019 } 4020 subsys_initcall(ksm_init); 4021