1 // SPDX-License-Identifier: GPL-2.0 2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 3 4 #include <linux/mm.h> 5 #include <linux/sched.h> 6 #include <linux/sched/mm.h> 7 #include <linux/sched/coredump.h> 8 #include <linux/mmu_notifier.h> 9 #include <linux/rmap.h> 10 #include <linux/swap.h> 11 #include <linux/mm_inline.h> 12 #include <linux/kthread.h> 13 #include <linux/khugepaged.h> 14 #include <linux/freezer.h> 15 #include <linux/mman.h> 16 #include <linux/hashtable.h> 17 #include <linux/userfaultfd_k.h> 18 #include <linux/page_idle.h> 19 #include <linux/swapops.h> 20 #include <linux/shmem_fs.h> 21 22 #include <asm/tlb.h> 23 #include <asm/pgalloc.h> 24 #include "internal.h" 25 26 enum scan_result { 27 SCAN_FAIL, 28 SCAN_SUCCEED, 29 SCAN_PMD_NULL, 30 SCAN_EXCEED_NONE_PTE, 31 SCAN_PTE_NON_PRESENT, 32 SCAN_PAGE_RO, 33 SCAN_LACK_REFERENCED_PAGE, 34 SCAN_PAGE_NULL, 35 SCAN_SCAN_ABORT, 36 SCAN_PAGE_COUNT, 37 SCAN_PAGE_LRU, 38 SCAN_PAGE_LOCK, 39 SCAN_PAGE_ANON, 40 SCAN_PAGE_COMPOUND, 41 SCAN_ANY_PROCESS, 42 SCAN_VMA_NULL, 43 SCAN_VMA_CHECK, 44 SCAN_ADDRESS_RANGE, 45 SCAN_SWAP_CACHE_PAGE, 46 SCAN_DEL_PAGE_LRU, 47 SCAN_ALLOC_HUGE_PAGE_FAIL, 48 SCAN_CGROUP_CHARGE_FAIL, 49 SCAN_EXCEED_SWAP_PTE, 50 SCAN_TRUNCATED, 51 SCAN_PAGE_HAS_PRIVATE, 52 }; 53 54 #define CREATE_TRACE_POINTS 55 #include <trace/events/huge_memory.h> 56 57 /* default scan 8*512 pte (or vmas) every 30 second */ 58 static unsigned int khugepaged_pages_to_scan __read_mostly; 59 static unsigned int khugepaged_pages_collapsed; 60 static unsigned int khugepaged_full_scans; 61 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000; 62 /* during fragmentation poll the hugepage allocator once every minute */ 63 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000; 64 static unsigned long khugepaged_sleep_expire; 65 static DEFINE_SPINLOCK(khugepaged_mm_lock); 66 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait); 67 /* 68 * default collapse hugepages if there is at least one pte mapped like 69 * it would have happened if the vma was large enough during page 70 * fault. 71 */ 72 static unsigned int khugepaged_max_ptes_none __read_mostly; 73 static unsigned int khugepaged_max_ptes_swap __read_mostly; 74 75 #define MM_SLOTS_HASH_BITS 10 76 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS); 77 78 static struct kmem_cache *mm_slot_cache __read_mostly; 79 80 #define MAX_PTE_MAPPED_THP 8 81 82 /** 83 * struct mm_slot - hash lookup from mm to mm_slot 84 * @hash: hash collision list 85 * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head 86 * @mm: the mm that this information is valid for 87 */ 88 struct mm_slot { 89 struct hlist_node hash; 90 struct list_head mm_node; 91 struct mm_struct *mm; 92 93 /* pte-mapped THP in this mm */ 94 int nr_pte_mapped_thp; 95 unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP]; 96 }; 97 98 /** 99 * struct khugepaged_scan - cursor for scanning 100 * @mm_head: the head of the mm list to scan 101 * @mm_slot: the current mm_slot we are scanning 102 * @address: the next address inside that to be scanned 103 * 104 * There is only the one khugepaged_scan instance of this cursor structure. 105 */ 106 struct khugepaged_scan { 107 struct list_head mm_head; 108 struct mm_slot *mm_slot; 109 unsigned long address; 110 }; 111 112 static struct khugepaged_scan khugepaged_scan = { 113 .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head), 114 }; 115 116 #ifdef CONFIG_SYSFS 117 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj, 118 struct kobj_attribute *attr, 119 char *buf) 120 { 121 return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs); 122 } 123 124 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj, 125 struct kobj_attribute *attr, 126 const char *buf, size_t count) 127 { 128 unsigned long msecs; 129 int err; 130 131 err = kstrtoul(buf, 10, &msecs); 132 if (err || msecs > UINT_MAX) 133 return -EINVAL; 134 135 khugepaged_scan_sleep_millisecs = msecs; 136 khugepaged_sleep_expire = 0; 137 wake_up_interruptible(&khugepaged_wait); 138 139 return count; 140 } 141 static struct kobj_attribute scan_sleep_millisecs_attr = 142 __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show, 143 scan_sleep_millisecs_store); 144 145 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj, 146 struct kobj_attribute *attr, 147 char *buf) 148 { 149 return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs); 150 } 151 152 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj, 153 struct kobj_attribute *attr, 154 const char *buf, size_t count) 155 { 156 unsigned long msecs; 157 int err; 158 159 err = kstrtoul(buf, 10, &msecs); 160 if (err || msecs > UINT_MAX) 161 return -EINVAL; 162 163 khugepaged_alloc_sleep_millisecs = msecs; 164 khugepaged_sleep_expire = 0; 165 wake_up_interruptible(&khugepaged_wait); 166 167 return count; 168 } 169 static struct kobj_attribute alloc_sleep_millisecs_attr = 170 __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show, 171 alloc_sleep_millisecs_store); 172 173 static ssize_t pages_to_scan_show(struct kobject *kobj, 174 struct kobj_attribute *attr, 175 char *buf) 176 { 177 return sprintf(buf, "%u\n", khugepaged_pages_to_scan); 178 } 179 static ssize_t pages_to_scan_store(struct kobject *kobj, 180 struct kobj_attribute *attr, 181 const char *buf, size_t count) 182 { 183 int err; 184 unsigned long pages; 185 186 err = kstrtoul(buf, 10, &pages); 187 if (err || !pages || pages > UINT_MAX) 188 return -EINVAL; 189 190 khugepaged_pages_to_scan = pages; 191 192 return count; 193 } 194 static struct kobj_attribute pages_to_scan_attr = 195 __ATTR(pages_to_scan, 0644, pages_to_scan_show, 196 pages_to_scan_store); 197 198 static ssize_t pages_collapsed_show(struct kobject *kobj, 199 struct kobj_attribute *attr, 200 char *buf) 201 { 202 return sprintf(buf, "%u\n", khugepaged_pages_collapsed); 203 } 204 static struct kobj_attribute pages_collapsed_attr = 205 __ATTR_RO(pages_collapsed); 206 207 static ssize_t full_scans_show(struct kobject *kobj, 208 struct kobj_attribute *attr, 209 char *buf) 210 { 211 return sprintf(buf, "%u\n", khugepaged_full_scans); 212 } 213 static struct kobj_attribute full_scans_attr = 214 __ATTR_RO(full_scans); 215 216 static ssize_t khugepaged_defrag_show(struct kobject *kobj, 217 struct kobj_attribute *attr, char *buf) 218 { 219 return single_hugepage_flag_show(kobj, attr, buf, 220 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG); 221 } 222 static ssize_t khugepaged_defrag_store(struct kobject *kobj, 223 struct kobj_attribute *attr, 224 const char *buf, size_t count) 225 { 226 return single_hugepage_flag_store(kobj, attr, buf, count, 227 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG); 228 } 229 static struct kobj_attribute khugepaged_defrag_attr = 230 __ATTR(defrag, 0644, khugepaged_defrag_show, 231 khugepaged_defrag_store); 232 233 /* 234 * max_ptes_none controls if khugepaged should collapse hugepages over 235 * any unmapped ptes in turn potentially increasing the memory 236 * footprint of the vmas. When max_ptes_none is 0 khugepaged will not 237 * reduce the available free memory in the system as it 238 * runs. Increasing max_ptes_none will instead potentially reduce the 239 * free memory in the system during the khugepaged scan. 240 */ 241 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj, 242 struct kobj_attribute *attr, 243 char *buf) 244 { 245 return sprintf(buf, "%u\n", khugepaged_max_ptes_none); 246 } 247 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj, 248 struct kobj_attribute *attr, 249 const char *buf, size_t count) 250 { 251 int err; 252 unsigned long max_ptes_none; 253 254 err = kstrtoul(buf, 10, &max_ptes_none); 255 if (err || max_ptes_none > HPAGE_PMD_NR-1) 256 return -EINVAL; 257 258 khugepaged_max_ptes_none = max_ptes_none; 259 260 return count; 261 } 262 static struct kobj_attribute khugepaged_max_ptes_none_attr = 263 __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show, 264 khugepaged_max_ptes_none_store); 265 266 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj, 267 struct kobj_attribute *attr, 268 char *buf) 269 { 270 return sprintf(buf, "%u\n", khugepaged_max_ptes_swap); 271 } 272 273 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj, 274 struct kobj_attribute *attr, 275 const char *buf, size_t count) 276 { 277 int err; 278 unsigned long max_ptes_swap; 279 280 err = kstrtoul(buf, 10, &max_ptes_swap); 281 if (err || max_ptes_swap > HPAGE_PMD_NR-1) 282 return -EINVAL; 283 284 khugepaged_max_ptes_swap = max_ptes_swap; 285 286 return count; 287 } 288 289 static struct kobj_attribute khugepaged_max_ptes_swap_attr = 290 __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show, 291 khugepaged_max_ptes_swap_store); 292 293 static struct attribute *khugepaged_attr[] = { 294 &khugepaged_defrag_attr.attr, 295 &khugepaged_max_ptes_none_attr.attr, 296 &pages_to_scan_attr.attr, 297 &pages_collapsed_attr.attr, 298 &full_scans_attr.attr, 299 &scan_sleep_millisecs_attr.attr, 300 &alloc_sleep_millisecs_attr.attr, 301 &khugepaged_max_ptes_swap_attr.attr, 302 NULL, 303 }; 304 305 struct attribute_group khugepaged_attr_group = { 306 .attrs = khugepaged_attr, 307 .name = "khugepaged", 308 }; 309 #endif /* CONFIG_SYSFS */ 310 311 #define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB) 312 313 int hugepage_madvise(struct vm_area_struct *vma, 314 unsigned long *vm_flags, int advice) 315 { 316 switch (advice) { 317 case MADV_HUGEPAGE: 318 #ifdef CONFIG_S390 319 /* 320 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390 321 * can't handle this properly after s390_enable_sie, so we simply 322 * ignore the madvise to prevent qemu from causing a SIGSEGV. 323 */ 324 if (mm_has_pgste(vma->vm_mm)) 325 return 0; 326 #endif 327 *vm_flags &= ~VM_NOHUGEPAGE; 328 *vm_flags |= VM_HUGEPAGE; 329 /* 330 * If the vma become good for khugepaged to scan, 331 * register it here without waiting a page fault that 332 * may not happen any time soon. 333 */ 334 if (!(*vm_flags & VM_NO_KHUGEPAGED) && 335 khugepaged_enter_vma_merge(vma, *vm_flags)) 336 return -ENOMEM; 337 break; 338 case MADV_NOHUGEPAGE: 339 *vm_flags &= ~VM_HUGEPAGE; 340 *vm_flags |= VM_NOHUGEPAGE; 341 /* 342 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning 343 * this vma even if we leave the mm registered in khugepaged if 344 * it got registered before VM_NOHUGEPAGE was set. 345 */ 346 break; 347 } 348 349 return 0; 350 } 351 352 int __init khugepaged_init(void) 353 { 354 mm_slot_cache = kmem_cache_create("khugepaged_mm_slot", 355 sizeof(struct mm_slot), 356 __alignof__(struct mm_slot), 0, NULL); 357 if (!mm_slot_cache) 358 return -ENOMEM; 359 360 khugepaged_pages_to_scan = HPAGE_PMD_NR * 8; 361 khugepaged_max_ptes_none = HPAGE_PMD_NR - 1; 362 khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8; 363 364 return 0; 365 } 366 367 void __init khugepaged_destroy(void) 368 { 369 kmem_cache_destroy(mm_slot_cache); 370 } 371 372 static inline struct mm_slot *alloc_mm_slot(void) 373 { 374 if (!mm_slot_cache) /* initialization failed */ 375 return NULL; 376 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); 377 } 378 379 static inline void free_mm_slot(struct mm_slot *mm_slot) 380 { 381 kmem_cache_free(mm_slot_cache, mm_slot); 382 } 383 384 static struct mm_slot *get_mm_slot(struct mm_struct *mm) 385 { 386 struct mm_slot *mm_slot; 387 388 hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm) 389 if (mm == mm_slot->mm) 390 return mm_slot; 391 392 return NULL; 393 } 394 395 static void insert_to_mm_slots_hash(struct mm_struct *mm, 396 struct mm_slot *mm_slot) 397 { 398 mm_slot->mm = mm; 399 hash_add(mm_slots_hash, &mm_slot->hash, (long)mm); 400 } 401 402 static inline int khugepaged_test_exit(struct mm_struct *mm) 403 { 404 return atomic_read(&mm->mm_users) == 0; 405 } 406 407 static bool hugepage_vma_check(struct vm_area_struct *vma, 408 unsigned long vm_flags) 409 { 410 if ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) || 411 (vm_flags & VM_NOHUGEPAGE) || 412 test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) 413 return false; 414 415 if (shmem_file(vma->vm_file) || 416 (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && 417 vma->vm_file && 418 (vm_flags & VM_DENYWRITE))) { 419 if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)) 420 return false; 421 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff, 422 HPAGE_PMD_NR); 423 } 424 if (!vma->anon_vma || vma->vm_ops) 425 return false; 426 if (is_vma_temporary_stack(vma)) 427 return false; 428 return !(vm_flags & VM_NO_KHUGEPAGED); 429 } 430 431 int __khugepaged_enter(struct mm_struct *mm) 432 { 433 struct mm_slot *mm_slot; 434 int wakeup; 435 436 mm_slot = alloc_mm_slot(); 437 if (!mm_slot) 438 return -ENOMEM; 439 440 /* __khugepaged_exit() must not run from under us */ 441 VM_BUG_ON_MM(khugepaged_test_exit(mm), mm); 442 if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) { 443 free_mm_slot(mm_slot); 444 return 0; 445 } 446 447 spin_lock(&khugepaged_mm_lock); 448 insert_to_mm_slots_hash(mm, mm_slot); 449 /* 450 * Insert just behind the scanning cursor, to let the area settle 451 * down a little. 452 */ 453 wakeup = list_empty(&khugepaged_scan.mm_head); 454 list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head); 455 spin_unlock(&khugepaged_mm_lock); 456 457 mmgrab(mm); 458 if (wakeup) 459 wake_up_interruptible(&khugepaged_wait); 460 461 return 0; 462 } 463 464 int khugepaged_enter_vma_merge(struct vm_area_struct *vma, 465 unsigned long vm_flags) 466 { 467 unsigned long hstart, hend; 468 469 /* 470 * khugepaged only supports read-only files for non-shmem files. 471 * khugepaged does not yet work on special mappings. And 472 * file-private shmem THP is not supported. 473 */ 474 if (!hugepage_vma_check(vma, vm_flags)) 475 return 0; 476 477 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; 478 hend = vma->vm_end & HPAGE_PMD_MASK; 479 if (hstart < hend) 480 return khugepaged_enter(vma, vm_flags); 481 return 0; 482 } 483 484 void __khugepaged_exit(struct mm_struct *mm) 485 { 486 struct mm_slot *mm_slot; 487 int free = 0; 488 489 spin_lock(&khugepaged_mm_lock); 490 mm_slot = get_mm_slot(mm); 491 if (mm_slot && khugepaged_scan.mm_slot != mm_slot) { 492 hash_del(&mm_slot->hash); 493 list_del(&mm_slot->mm_node); 494 free = 1; 495 } 496 spin_unlock(&khugepaged_mm_lock); 497 498 if (free) { 499 clear_bit(MMF_VM_HUGEPAGE, &mm->flags); 500 free_mm_slot(mm_slot); 501 mmdrop(mm); 502 } else if (mm_slot) { 503 /* 504 * This is required to serialize against 505 * khugepaged_test_exit() (which is guaranteed to run 506 * under mmap sem read mode). Stop here (after we 507 * return all pagetables will be destroyed) until 508 * khugepaged has finished working on the pagetables 509 * under the mmap_sem. 510 */ 511 down_write(&mm->mmap_sem); 512 up_write(&mm->mmap_sem); 513 } 514 } 515 516 static void release_pte_page(struct page *page) 517 { 518 dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page)); 519 unlock_page(page); 520 putback_lru_page(page); 521 } 522 523 static void release_pte_pages(pte_t *pte, pte_t *_pte) 524 { 525 while (--_pte >= pte) { 526 pte_t pteval = *_pte; 527 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval))) 528 release_pte_page(pte_page(pteval)); 529 } 530 } 531 532 static int __collapse_huge_page_isolate(struct vm_area_struct *vma, 533 unsigned long address, 534 pte_t *pte) 535 { 536 struct page *page = NULL; 537 pte_t *_pte; 538 int none_or_zero = 0, result = 0, referenced = 0; 539 bool writable = false; 540 541 for (_pte = pte; _pte < pte+HPAGE_PMD_NR; 542 _pte++, address += PAGE_SIZE) { 543 pte_t pteval = *_pte; 544 if (pte_none(pteval) || (pte_present(pteval) && 545 is_zero_pfn(pte_pfn(pteval)))) { 546 if (!userfaultfd_armed(vma) && 547 ++none_or_zero <= khugepaged_max_ptes_none) { 548 continue; 549 } else { 550 result = SCAN_EXCEED_NONE_PTE; 551 goto out; 552 } 553 } 554 if (!pte_present(pteval)) { 555 result = SCAN_PTE_NON_PRESENT; 556 goto out; 557 } 558 page = vm_normal_page(vma, address, pteval); 559 if (unlikely(!page)) { 560 result = SCAN_PAGE_NULL; 561 goto out; 562 } 563 564 /* TODO: teach khugepaged to collapse THP mapped with pte */ 565 if (PageCompound(page)) { 566 result = SCAN_PAGE_COMPOUND; 567 goto out; 568 } 569 570 VM_BUG_ON_PAGE(!PageAnon(page), page); 571 572 /* 573 * We can do it before isolate_lru_page because the 574 * page can't be freed from under us. NOTE: PG_lock 575 * is needed to serialize against split_huge_page 576 * when invoked from the VM. 577 */ 578 if (!trylock_page(page)) { 579 result = SCAN_PAGE_LOCK; 580 goto out; 581 } 582 583 /* 584 * cannot use mapcount: can't collapse if there's a gup pin. 585 * The page must only be referenced by the scanned process 586 * and page swap cache. 587 */ 588 if (page_count(page) != 1 + PageSwapCache(page)) { 589 unlock_page(page); 590 result = SCAN_PAGE_COUNT; 591 goto out; 592 } 593 if (pte_write(pteval)) { 594 writable = true; 595 } else { 596 if (PageSwapCache(page) && 597 !reuse_swap_page(page, NULL)) { 598 unlock_page(page); 599 result = SCAN_SWAP_CACHE_PAGE; 600 goto out; 601 } 602 /* 603 * Page is not in the swap cache. It can be collapsed 604 * into a THP. 605 */ 606 } 607 608 /* 609 * Isolate the page to avoid collapsing an hugepage 610 * currently in use by the VM. 611 */ 612 if (isolate_lru_page(page)) { 613 unlock_page(page); 614 result = SCAN_DEL_PAGE_LRU; 615 goto out; 616 } 617 inc_node_page_state(page, 618 NR_ISOLATED_ANON + page_is_file_cache(page)); 619 VM_BUG_ON_PAGE(!PageLocked(page), page); 620 VM_BUG_ON_PAGE(PageLRU(page), page); 621 622 /* There should be enough young pte to collapse the page */ 623 if (pte_young(pteval) || 624 page_is_young(page) || PageReferenced(page) || 625 mmu_notifier_test_young(vma->vm_mm, address)) 626 referenced++; 627 } 628 if (likely(writable)) { 629 if (likely(referenced)) { 630 result = SCAN_SUCCEED; 631 trace_mm_collapse_huge_page_isolate(page, none_or_zero, 632 referenced, writable, result); 633 return 1; 634 } 635 } else { 636 result = SCAN_PAGE_RO; 637 } 638 639 out: 640 release_pte_pages(pte, _pte); 641 trace_mm_collapse_huge_page_isolate(page, none_or_zero, 642 referenced, writable, result); 643 return 0; 644 } 645 646 static void __collapse_huge_page_copy(pte_t *pte, struct page *page, 647 struct vm_area_struct *vma, 648 unsigned long address, 649 spinlock_t *ptl) 650 { 651 pte_t *_pte; 652 for (_pte = pte; _pte < pte + HPAGE_PMD_NR; 653 _pte++, page++, address += PAGE_SIZE) { 654 pte_t pteval = *_pte; 655 struct page *src_page; 656 657 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { 658 clear_user_highpage(page, address); 659 add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); 660 if (is_zero_pfn(pte_pfn(pteval))) { 661 /* 662 * ptl mostly unnecessary. 663 */ 664 spin_lock(ptl); 665 /* 666 * paravirt calls inside pte_clear here are 667 * superfluous. 668 */ 669 pte_clear(vma->vm_mm, address, _pte); 670 spin_unlock(ptl); 671 } 672 } else { 673 src_page = pte_page(pteval); 674 copy_user_highpage(page, src_page, address, vma); 675 VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page); 676 release_pte_page(src_page); 677 /* 678 * ptl mostly unnecessary, but preempt has to 679 * be disabled to update the per-cpu stats 680 * inside page_remove_rmap(). 681 */ 682 spin_lock(ptl); 683 /* 684 * paravirt calls inside pte_clear here are 685 * superfluous. 686 */ 687 pte_clear(vma->vm_mm, address, _pte); 688 page_remove_rmap(src_page, false); 689 spin_unlock(ptl); 690 free_page_and_swap_cache(src_page); 691 } 692 } 693 } 694 695 static void khugepaged_alloc_sleep(void) 696 { 697 DEFINE_WAIT(wait); 698 699 add_wait_queue(&khugepaged_wait, &wait); 700 freezable_schedule_timeout_interruptible( 701 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs)); 702 remove_wait_queue(&khugepaged_wait, &wait); 703 } 704 705 static int khugepaged_node_load[MAX_NUMNODES]; 706 707 static bool khugepaged_scan_abort(int nid) 708 { 709 int i; 710 711 /* 712 * If node_reclaim_mode is disabled, then no extra effort is made to 713 * allocate memory locally. 714 */ 715 if (!node_reclaim_mode) 716 return false; 717 718 /* If there is a count for this node already, it must be acceptable */ 719 if (khugepaged_node_load[nid]) 720 return false; 721 722 for (i = 0; i < MAX_NUMNODES; i++) { 723 if (!khugepaged_node_load[i]) 724 continue; 725 if (node_distance(nid, i) > node_reclaim_distance) 726 return true; 727 } 728 return false; 729 } 730 731 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */ 732 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void) 733 { 734 return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT; 735 } 736 737 #ifdef CONFIG_NUMA 738 static int khugepaged_find_target_node(void) 739 { 740 static int last_khugepaged_target_node = NUMA_NO_NODE; 741 int nid, target_node = 0, max_value = 0; 742 743 /* find first node with max normal pages hit */ 744 for (nid = 0; nid < MAX_NUMNODES; nid++) 745 if (khugepaged_node_load[nid] > max_value) { 746 max_value = khugepaged_node_load[nid]; 747 target_node = nid; 748 } 749 750 /* do some balance if several nodes have the same hit record */ 751 if (target_node <= last_khugepaged_target_node) 752 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES; 753 nid++) 754 if (max_value == khugepaged_node_load[nid]) { 755 target_node = nid; 756 break; 757 } 758 759 last_khugepaged_target_node = target_node; 760 return target_node; 761 } 762 763 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait) 764 { 765 if (IS_ERR(*hpage)) { 766 if (!*wait) 767 return false; 768 769 *wait = false; 770 *hpage = NULL; 771 khugepaged_alloc_sleep(); 772 } else if (*hpage) { 773 put_page(*hpage); 774 *hpage = NULL; 775 } 776 777 return true; 778 } 779 780 static struct page * 781 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node) 782 { 783 VM_BUG_ON_PAGE(*hpage, *hpage); 784 785 *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER); 786 if (unlikely(!*hpage)) { 787 count_vm_event(THP_COLLAPSE_ALLOC_FAILED); 788 *hpage = ERR_PTR(-ENOMEM); 789 return NULL; 790 } 791 792 prep_transhuge_page(*hpage); 793 count_vm_event(THP_COLLAPSE_ALLOC); 794 return *hpage; 795 } 796 #else 797 static int khugepaged_find_target_node(void) 798 { 799 return 0; 800 } 801 802 static inline struct page *alloc_khugepaged_hugepage(void) 803 { 804 struct page *page; 805 806 page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(), 807 HPAGE_PMD_ORDER); 808 if (page) 809 prep_transhuge_page(page); 810 return page; 811 } 812 813 static struct page *khugepaged_alloc_hugepage(bool *wait) 814 { 815 struct page *hpage; 816 817 do { 818 hpage = alloc_khugepaged_hugepage(); 819 if (!hpage) { 820 count_vm_event(THP_COLLAPSE_ALLOC_FAILED); 821 if (!*wait) 822 return NULL; 823 824 *wait = false; 825 khugepaged_alloc_sleep(); 826 } else 827 count_vm_event(THP_COLLAPSE_ALLOC); 828 } while (unlikely(!hpage) && likely(khugepaged_enabled())); 829 830 return hpage; 831 } 832 833 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait) 834 { 835 if (!*hpage) 836 *hpage = khugepaged_alloc_hugepage(wait); 837 838 if (unlikely(!*hpage)) 839 return false; 840 841 return true; 842 } 843 844 static struct page * 845 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node) 846 { 847 VM_BUG_ON(!*hpage); 848 849 return *hpage; 850 } 851 #endif 852 853 /* 854 * If mmap_sem temporarily dropped, revalidate vma 855 * before taking mmap_sem. 856 * Return 0 if succeeds, otherwise return none-zero 857 * value (scan code). 858 */ 859 860 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, 861 struct vm_area_struct **vmap) 862 { 863 struct vm_area_struct *vma; 864 unsigned long hstart, hend; 865 866 if (unlikely(khugepaged_test_exit(mm))) 867 return SCAN_ANY_PROCESS; 868 869 *vmap = vma = find_vma(mm, address); 870 if (!vma) 871 return SCAN_VMA_NULL; 872 873 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; 874 hend = vma->vm_end & HPAGE_PMD_MASK; 875 if (address < hstart || address + HPAGE_PMD_SIZE > hend) 876 return SCAN_ADDRESS_RANGE; 877 if (!hugepage_vma_check(vma, vma->vm_flags)) 878 return SCAN_VMA_CHECK; 879 return 0; 880 } 881 882 /* 883 * Bring missing pages in from swap, to complete THP collapse. 884 * Only done if khugepaged_scan_pmd believes it is worthwhile. 885 * 886 * Called and returns without pte mapped or spinlocks held, 887 * but with mmap_sem held to protect against vma changes. 888 */ 889 890 static bool __collapse_huge_page_swapin(struct mm_struct *mm, 891 struct vm_area_struct *vma, 892 unsigned long address, pmd_t *pmd, 893 int referenced) 894 { 895 int swapped_in = 0; 896 vm_fault_t ret = 0; 897 struct vm_fault vmf = { 898 .vma = vma, 899 .address = address, 900 .flags = FAULT_FLAG_ALLOW_RETRY, 901 .pmd = pmd, 902 .pgoff = linear_page_index(vma, address), 903 }; 904 905 /* we only decide to swapin, if there is enough young ptes */ 906 if (referenced < HPAGE_PMD_NR/2) { 907 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); 908 return false; 909 } 910 vmf.pte = pte_offset_map(pmd, address); 911 for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE; 912 vmf.pte++, vmf.address += PAGE_SIZE) { 913 vmf.orig_pte = *vmf.pte; 914 if (!is_swap_pte(vmf.orig_pte)) 915 continue; 916 swapped_in++; 917 ret = do_swap_page(&vmf); 918 919 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */ 920 if (ret & VM_FAULT_RETRY) { 921 down_read(&mm->mmap_sem); 922 if (hugepage_vma_revalidate(mm, address, &vmf.vma)) { 923 /* vma is no longer available, don't continue to swapin */ 924 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); 925 return false; 926 } 927 /* check if the pmd is still valid */ 928 if (mm_find_pmd(mm, address) != pmd) { 929 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); 930 return false; 931 } 932 } 933 if (ret & VM_FAULT_ERROR) { 934 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); 935 return false; 936 } 937 /* pte is unmapped now, we need to map it */ 938 vmf.pte = pte_offset_map(pmd, vmf.address); 939 } 940 vmf.pte--; 941 pte_unmap(vmf.pte); 942 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1); 943 return true; 944 } 945 946 static void collapse_huge_page(struct mm_struct *mm, 947 unsigned long address, 948 struct page **hpage, 949 int node, int referenced) 950 { 951 pmd_t *pmd, _pmd; 952 pte_t *pte; 953 pgtable_t pgtable; 954 struct page *new_page; 955 spinlock_t *pmd_ptl, *pte_ptl; 956 int isolated = 0, result = 0; 957 struct mem_cgroup *memcg; 958 struct vm_area_struct *vma; 959 struct mmu_notifier_range range; 960 gfp_t gfp; 961 962 VM_BUG_ON(address & ~HPAGE_PMD_MASK); 963 964 /* Only allocate from the target node */ 965 gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE; 966 967 /* 968 * Before allocating the hugepage, release the mmap_sem read lock. 969 * The allocation can take potentially a long time if it involves 970 * sync compaction, and we do not need to hold the mmap_sem during 971 * that. We will recheck the vma after taking it again in write mode. 972 */ 973 up_read(&mm->mmap_sem); 974 new_page = khugepaged_alloc_page(hpage, gfp, node); 975 if (!new_page) { 976 result = SCAN_ALLOC_HUGE_PAGE_FAIL; 977 goto out_nolock; 978 } 979 980 if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) { 981 result = SCAN_CGROUP_CHARGE_FAIL; 982 goto out_nolock; 983 } 984 985 down_read(&mm->mmap_sem); 986 result = hugepage_vma_revalidate(mm, address, &vma); 987 if (result) { 988 mem_cgroup_cancel_charge(new_page, memcg, true); 989 up_read(&mm->mmap_sem); 990 goto out_nolock; 991 } 992 993 pmd = mm_find_pmd(mm, address); 994 if (!pmd) { 995 result = SCAN_PMD_NULL; 996 mem_cgroup_cancel_charge(new_page, memcg, true); 997 up_read(&mm->mmap_sem); 998 goto out_nolock; 999 } 1000 1001 /* 1002 * __collapse_huge_page_swapin always returns with mmap_sem locked. 1003 * If it fails, we release mmap_sem and jump out_nolock. 1004 * Continuing to collapse causes inconsistency. 1005 */ 1006 if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) { 1007 mem_cgroup_cancel_charge(new_page, memcg, true); 1008 up_read(&mm->mmap_sem); 1009 goto out_nolock; 1010 } 1011 1012 up_read(&mm->mmap_sem); 1013 /* 1014 * Prevent all access to pagetables with the exception of 1015 * gup_fast later handled by the ptep_clear_flush and the VM 1016 * handled by the anon_vma lock + PG_lock. 1017 */ 1018 down_write(&mm->mmap_sem); 1019 result = SCAN_ANY_PROCESS; 1020 if (!mmget_still_valid(mm)) 1021 goto out; 1022 result = hugepage_vma_revalidate(mm, address, &vma); 1023 if (result) 1024 goto out; 1025 /* check if the pmd is still valid */ 1026 if (mm_find_pmd(mm, address) != pmd) 1027 goto out; 1028 1029 anon_vma_lock_write(vma->anon_vma); 1030 1031 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, 1032 address, address + HPAGE_PMD_SIZE); 1033 mmu_notifier_invalidate_range_start(&range); 1034 1035 pte = pte_offset_map(pmd, address); 1036 pte_ptl = pte_lockptr(mm, pmd); 1037 1038 pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */ 1039 /* 1040 * After this gup_fast can't run anymore. This also removes 1041 * any huge TLB entry from the CPU so we won't allow 1042 * huge and small TLB entries for the same virtual address 1043 * to avoid the risk of CPU bugs in that area. 1044 */ 1045 _pmd = pmdp_collapse_flush(vma, address, pmd); 1046 spin_unlock(pmd_ptl); 1047 mmu_notifier_invalidate_range_end(&range); 1048 1049 spin_lock(pte_ptl); 1050 isolated = __collapse_huge_page_isolate(vma, address, pte); 1051 spin_unlock(pte_ptl); 1052 1053 if (unlikely(!isolated)) { 1054 pte_unmap(pte); 1055 spin_lock(pmd_ptl); 1056 BUG_ON(!pmd_none(*pmd)); 1057 /* 1058 * We can only use set_pmd_at when establishing 1059 * hugepmds and never for establishing regular pmds that 1060 * points to regular pagetables. Use pmd_populate for that 1061 */ 1062 pmd_populate(mm, pmd, pmd_pgtable(_pmd)); 1063 spin_unlock(pmd_ptl); 1064 anon_vma_unlock_write(vma->anon_vma); 1065 result = SCAN_FAIL; 1066 goto out; 1067 } 1068 1069 /* 1070 * All pages are isolated and locked so anon_vma rmap 1071 * can't run anymore. 1072 */ 1073 anon_vma_unlock_write(vma->anon_vma); 1074 1075 __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl); 1076 pte_unmap(pte); 1077 __SetPageUptodate(new_page); 1078 pgtable = pmd_pgtable(_pmd); 1079 1080 _pmd = mk_huge_pmd(new_page, vma->vm_page_prot); 1081 _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma); 1082 1083 /* 1084 * spin_lock() below is not the equivalent of smp_wmb(), so 1085 * this is needed to avoid the copy_huge_page writes to become 1086 * visible after the set_pmd_at() write. 1087 */ 1088 smp_wmb(); 1089 1090 spin_lock(pmd_ptl); 1091 BUG_ON(!pmd_none(*pmd)); 1092 page_add_new_anon_rmap(new_page, vma, address, true); 1093 mem_cgroup_commit_charge(new_page, memcg, false, true); 1094 count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1); 1095 lru_cache_add_active_or_unevictable(new_page, vma); 1096 pgtable_trans_huge_deposit(mm, pmd, pgtable); 1097 set_pmd_at(mm, address, pmd, _pmd); 1098 update_mmu_cache_pmd(vma, address, pmd); 1099 spin_unlock(pmd_ptl); 1100 1101 *hpage = NULL; 1102 1103 khugepaged_pages_collapsed++; 1104 result = SCAN_SUCCEED; 1105 out_up_write: 1106 up_write(&mm->mmap_sem); 1107 out_nolock: 1108 trace_mm_collapse_huge_page(mm, isolated, result); 1109 return; 1110 out: 1111 mem_cgroup_cancel_charge(new_page, memcg, true); 1112 goto out_up_write; 1113 } 1114 1115 static int khugepaged_scan_pmd(struct mm_struct *mm, 1116 struct vm_area_struct *vma, 1117 unsigned long address, 1118 struct page **hpage) 1119 { 1120 pmd_t *pmd; 1121 pte_t *pte, *_pte; 1122 int ret = 0, none_or_zero = 0, result = 0, referenced = 0; 1123 struct page *page = NULL; 1124 unsigned long _address; 1125 spinlock_t *ptl; 1126 int node = NUMA_NO_NODE, unmapped = 0; 1127 bool writable = false; 1128 1129 VM_BUG_ON(address & ~HPAGE_PMD_MASK); 1130 1131 pmd = mm_find_pmd(mm, address); 1132 if (!pmd) { 1133 result = SCAN_PMD_NULL; 1134 goto out; 1135 } 1136 1137 memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load)); 1138 pte = pte_offset_map_lock(mm, pmd, address, &ptl); 1139 for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR; 1140 _pte++, _address += PAGE_SIZE) { 1141 pte_t pteval = *_pte; 1142 if (is_swap_pte(pteval)) { 1143 if (++unmapped <= khugepaged_max_ptes_swap) { 1144 continue; 1145 } else { 1146 result = SCAN_EXCEED_SWAP_PTE; 1147 goto out_unmap; 1148 } 1149 } 1150 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { 1151 if (!userfaultfd_armed(vma) && 1152 ++none_or_zero <= khugepaged_max_ptes_none) { 1153 continue; 1154 } else { 1155 result = SCAN_EXCEED_NONE_PTE; 1156 goto out_unmap; 1157 } 1158 } 1159 if (!pte_present(pteval)) { 1160 result = SCAN_PTE_NON_PRESENT; 1161 goto out_unmap; 1162 } 1163 if (pte_write(pteval)) 1164 writable = true; 1165 1166 page = vm_normal_page(vma, _address, pteval); 1167 if (unlikely(!page)) { 1168 result = SCAN_PAGE_NULL; 1169 goto out_unmap; 1170 } 1171 1172 /* TODO: teach khugepaged to collapse THP mapped with pte */ 1173 if (PageCompound(page)) { 1174 result = SCAN_PAGE_COMPOUND; 1175 goto out_unmap; 1176 } 1177 1178 /* 1179 * Record which node the original page is from and save this 1180 * information to khugepaged_node_load[]. 1181 * Khupaged will allocate hugepage from the node has the max 1182 * hit record. 1183 */ 1184 node = page_to_nid(page); 1185 if (khugepaged_scan_abort(node)) { 1186 result = SCAN_SCAN_ABORT; 1187 goto out_unmap; 1188 } 1189 khugepaged_node_load[node]++; 1190 if (!PageLRU(page)) { 1191 result = SCAN_PAGE_LRU; 1192 goto out_unmap; 1193 } 1194 if (PageLocked(page)) { 1195 result = SCAN_PAGE_LOCK; 1196 goto out_unmap; 1197 } 1198 if (!PageAnon(page)) { 1199 result = SCAN_PAGE_ANON; 1200 goto out_unmap; 1201 } 1202 1203 /* 1204 * cannot use mapcount: can't collapse if there's a gup pin. 1205 * The page must only be referenced by the scanned process 1206 * and page swap cache. 1207 */ 1208 if (page_count(page) != 1 + PageSwapCache(page)) { 1209 result = SCAN_PAGE_COUNT; 1210 goto out_unmap; 1211 } 1212 if (pte_young(pteval) || 1213 page_is_young(page) || PageReferenced(page) || 1214 mmu_notifier_test_young(vma->vm_mm, address)) 1215 referenced++; 1216 } 1217 if (writable) { 1218 if (referenced) { 1219 result = SCAN_SUCCEED; 1220 ret = 1; 1221 } else { 1222 result = SCAN_LACK_REFERENCED_PAGE; 1223 } 1224 } else { 1225 result = SCAN_PAGE_RO; 1226 } 1227 out_unmap: 1228 pte_unmap_unlock(pte, ptl); 1229 if (ret) { 1230 node = khugepaged_find_target_node(); 1231 /* collapse_huge_page will return with the mmap_sem released */ 1232 collapse_huge_page(mm, address, hpage, node, referenced); 1233 } 1234 out: 1235 trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, 1236 none_or_zero, result, unmapped); 1237 return ret; 1238 } 1239 1240 static void collect_mm_slot(struct mm_slot *mm_slot) 1241 { 1242 struct mm_struct *mm = mm_slot->mm; 1243 1244 lockdep_assert_held(&khugepaged_mm_lock); 1245 1246 if (khugepaged_test_exit(mm)) { 1247 /* free mm_slot */ 1248 hash_del(&mm_slot->hash); 1249 list_del(&mm_slot->mm_node); 1250 1251 /* 1252 * Not strictly needed because the mm exited already. 1253 * 1254 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags); 1255 */ 1256 1257 /* khugepaged_mm_lock actually not necessary for the below */ 1258 free_mm_slot(mm_slot); 1259 mmdrop(mm); 1260 } 1261 } 1262 1263 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE) 1264 /* 1265 * Notify khugepaged that given addr of the mm is pte-mapped THP. Then 1266 * khugepaged should try to collapse the page table. 1267 */ 1268 static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm, 1269 unsigned long addr) 1270 { 1271 struct mm_slot *mm_slot; 1272 1273 VM_BUG_ON(addr & ~HPAGE_PMD_MASK); 1274 1275 spin_lock(&khugepaged_mm_lock); 1276 mm_slot = get_mm_slot(mm); 1277 if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP)) 1278 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr; 1279 spin_unlock(&khugepaged_mm_lock); 1280 return 0; 1281 } 1282 1283 /** 1284 * Try to collapse a pte-mapped THP for mm at address haddr. 1285 * 1286 * This function checks whether all the PTEs in the PMD are pointing to the 1287 * right THP. If so, retract the page table so the THP can refault in with 1288 * as pmd-mapped. 1289 */ 1290 void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr) 1291 { 1292 unsigned long haddr = addr & HPAGE_PMD_MASK; 1293 struct vm_area_struct *vma = find_vma(mm, haddr); 1294 struct page *hpage = NULL; 1295 pte_t *start_pte, *pte; 1296 pmd_t *pmd, _pmd; 1297 spinlock_t *ptl; 1298 int count = 0; 1299 int i; 1300 1301 if (!vma || !vma->vm_file || 1302 vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE) 1303 return; 1304 1305 /* 1306 * This vm_flags may not have VM_HUGEPAGE if the page was not 1307 * collapsed by this mm. But we can still collapse if the page is 1308 * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check() 1309 * will not fail the vma for missing VM_HUGEPAGE 1310 */ 1311 if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE)) 1312 return; 1313 1314 pmd = mm_find_pmd(mm, haddr); 1315 if (!pmd) 1316 return; 1317 1318 start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl); 1319 1320 /* step 1: check all mapped PTEs are to the right huge page */ 1321 for (i = 0, addr = haddr, pte = start_pte; 1322 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) { 1323 struct page *page; 1324 1325 /* empty pte, skip */ 1326 if (pte_none(*pte)) 1327 continue; 1328 1329 /* page swapped out, abort */ 1330 if (!pte_present(*pte)) 1331 goto abort; 1332 1333 page = vm_normal_page(vma, addr, *pte); 1334 1335 if (!page || !PageCompound(page)) 1336 goto abort; 1337 1338 if (!hpage) { 1339 hpage = compound_head(page); 1340 /* 1341 * The mapping of the THP should not change. 1342 * 1343 * Note that uprobe, debugger, or MAP_PRIVATE may 1344 * change the page table, but the new page will 1345 * not pass PageCompound() check. 1346 */ 1347 if (WARN_ON(hpage->mapping != vma->vm_file->f_mapping)) 1348 goto abort; 1349 } 1350 1351 /* 1352 * Confirm the page maps to the correct subpage. 1353 * 1354 * Note that uprobe, debugger, or MAP_PRIVATE may change 1355 * the page table, but the new page will not pass 1356 * PageCompound() check. 1357 */ 1358 if (WARN_ON(hpage + i != page)) 1359 goto abort; 1360 count++; 1361 } 1362 1363 /* step 2: adjust rmap */ 1364 for (i = 0, addr = haddr, pte = start_pte; 1365 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) { 1366 struct page *page; 1367 1368 if (pte_none(*pte)) 1369 continue; 1370 page = vm_normal_page(vma, addr, *pte); 1371 page_remove_rmap(page, false); 1372 } 1373 1374 pte_unmap_unlock(start_pte, ptl); 1375 1376 /* step 3: set proper refcount and mm_counters. */ 1377 if (hpage) { 1378 page_ref_sub(hpage, count); 1379 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count); 1380 } 1381 1382 /* step 4: collapse pmd */ 1383 ptl = pmd_lock(vma->vm_mm, pmd); 1384 _pmd = pmdp_collapse_flush(vma, addr, pmd); 1385 spin_unlock(ptl); 1386 mm_dec_nr_ptes(mm); 1387 pte_free(mm, pmd_pgtable(_pmd)); 1388 return; 1389 1390 abort: 1391 pte_unmap_unlock(start_pte, ptl); 1392 } 1393 1394 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot) 1395 { 1396 struct mm_struct *mm = mm_slot->mm; 1397 int i; 1398 1399 if (likely(mm_slot->nr_pte_mapped_thp == 0)) 1400 return 0; 1401 1402 if (!down_write_trylock(&mm->mmap_sem)) 1403 return -EBUSY; 1404 1405 if (unlikely(khugepaged_test_exit(mm))) 1406 goto out; 1407 1408 for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++) 1409 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]); 1410 1411 out: 1412 mm_slot->nr_pte_mapped_thp = 0; 1413 up_write(&mm->mmap_sem); 1414 return 0; 1415 } 1416 1417 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) 1418 { 1419 struct vm_area_struct *vma; 1420 unsigned long addr; 1421 pmd_t *pmd, _pmd; 1422 1423 i_mmap_lock_write(mapping); 1424 vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) { 1425 /* 1426 * Check vma->anon_vma to exclude MAP_PRIVATE mappings that 1427 * got written to. These VMAs are likely not worth investing 1428 * down_write(mmap_sem) as PMD-mapping is likely to be split 1429 * later. 1430 * 1431 * Not that vma->anon_vma check is racy: it can be set up after 1432 * the check but before we took mmap_sem by the fault path. 1433 * But page lock would prevent establishing any new ptes of the 1434 * page, so we are safe. 1435 * 1436 * An alternative would be drop the check, but check that page 1437 * table is clear before calling pmdp_collapse_flush() under 1438 * ptl. It has higher chance to recover THP for the VMA, but 1439 * has higher cost too. 1440 */ 1441 if (vma->anon_vma) 1442 continue; 1443 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); 1444 if (addr & ~HPAGE_PMD_MASK) 1445 continue; 1446 if (vma->vm_end < addr + HPAGE_PMD_SIZE) 1447 continue; 1448 pmd = mm_find_pmd(vma->vm_mm, addr); 1449 if (!pmd) 1450 continue; 1451 /* 1452 * We need exclusive mmap_sem to retract page table. 1453 * 1454 * We use trylock due to lock inversion: we need to acquire 1455 * mmap_sem while holding page lock. Fault path does it in 1456 * reverse order. Trylock is a way to avoid deadlock. 1457 */ 1458 if (down_write_trylock(&vma->vm_mm->mmap_sem)) { 1459 spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd); 1460 /* assume page table is clear */ 1461 _pmd = pmdp_collapse_flush(vma, addr, pmd); 1462 spin_unlock(ptl); 1463 up_write(&vma->vm_mm->mmap_sem); 1464 mm_dec_nr_ptes(vma->vm_mm); 1465 pte_free(vma->vm_mm, pmd_pgtable(_pmd)); 1466 } else { 1467 /* Try again later */ 1468 khugepaged_add_pte_mapped_thp(vma->vm_mm, addr); 1469 } 1470 } 1471 i_mmap_unlock_write(mapping); 1472 } 1473 1474 /** 1475 * collapse_file - collapse filemap/tmpfs/shmem pages into huge one. 1476 * 1477 * Basic scheme is simple, details are more complex: 1478 * - allocate and lock a new huge page; 1479 * - scan page cache replacing old pages with the new one 1480 * + swap/gup in pages if necessary; 1481 * + fill in gaps; 1482 * + keep old pages around in case rollback is required; 1483 * - if replacing succeeds: 1484 * + copy data over; 1485 * + free old pages; 1486 * + unlock huge page; 1487 * - if replacing failed; 1488 * + put all pages back and unfreeze them; 1489 * + restore gaps in the page cache; 1490 * + unlock and free huge page; 1491 */ 1492 static void collapse_file(struct mm_struct *mm, 1493 struct file *file, pgoff_t start, 1494 struct page **hpage, int node) 1495 { 1496 struct address_space *mapping = file->f_mapping; 1497 gfp_t gfp; 1498 struct page *new_page; 1499 struct mem_cgroup *memcg; 1500 pgoff_t index, end = start + HPAGE_PMD_NR; 1501 LIST_HEAD(pagelist); 1502 XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER); 1503 int nr_none = 0, result = SCAN_SUCCEED; 1504 bool is_shmem = shmem_file(file); 1505 1506 VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); 1507 VM_BUG_ON(start & (HPAGE_PMD_NR - 1)); 1508 1509 /* Only allocate from the target node */ 1510 gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE; 1511 1512 new_page = khugepaged_alloc_page(hpage, gfp, node); 1513 if (!new_page) { 1514 result = SCAN_ALLOC_HUGE_PAGE_FAIL; 1515 goto out; 1516 } 1517 1518 if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) { 1519 result = SCAN_CGROUP_CHARGE_FAIL; 1520 goto out; 1521 } 1522 1523 /* This will be less messy when we use multi-index entries */ 1524 do { 1525 xas_lock_irq(&xas); 1526 xas_create_range(&xas); 1527 if (!xas_error(&xas)) 1528 break; 1529 xas_unlock_irq(&xas); 1530 if (!xas_nomem(&xas, GFP_KERNEL)) { 1531 mem_cgroup_cancel_charge(new_page, memcg, true); 1532 result = SCAN_FAIL; 1533 goto out; 1534 } 1535 } while (1); 1536 1537 __SetPageLocked(new_page); 1538 if (is_shmem) 1539 __SetPageSwapBacked(new_page); 1540 new_page->index = start; 1541 new_page->mapping = mapping; 1542 1543 /* 1544 * At this point the new_page is locked and not up-to-date. 1545 * It's safe to insert it into the page cache, because nobody would 1546 * be able to map it or use it in another way until we unlock it. 1547 */ 1548 1549 xas_set(&xas, start); 1550 for (index = start; index < end; index++) { 1551 struct page *page = xas_next(&xas); 1552 1553 VM_BUG_ON(index != xas.xa_index); 1554 if (is_shmem) { 1555 if (!page) { 1556 /* 1557 * Stop if extent has been truncated or 1558 * hole-punched, and is now completely 1559 * empty. 1560 */ 1561 if (index == start) { 1562 if (!xas_next_entry(&xas, end - 1)) { 1563 result = SCAN_TRUNCATED; 1564 goto xa_locked; 1565 } 1566 xas_set(&xas, index); 1567 } 1568 if (!shmem_charge(mapping->host, 1)) { 1569 result = SCAN_FAIL; 1570 goto xa_locked; 1571 } 1572 xas_store(&xas, new_page); 1573 nr_none++; 1574 continue; 1575 } 1576 1577 if (xa_is_value(page) || !PageUptodate(page)) { 1578 xas_unlock_irq(&xas); 1579 /* swap in or instantiate fallocated page */ 1580 if (shmem_getpage(mapping->host, index, &page, 1581 SGP_NOHUGE)) { 1582 result = SCAN_FAIL; 1583 goto xa_unlocked; 1584 } 1585 } else if (trylock_page(page)) { 1586 get_page(page); 1587 xas_unlock_irq(&xas); 1588 } else { 1589 result = SCAN_PAGE_LOCK; 1590 goto xa_locked; 1591 } 1592 } else { /* !is_shmem */ 1593 if (!page || xa_is_value(page)) { 1594 xas_unlock_irq(&xas); 1595 page_cache_sync_readahead(mapping, &file->f_ra, 1596 file, index, 1597 PAGE_SIZE); 1598 /* drain pagevecs to help isolate_lru_page() */ 1599 lru_add_drain(); 1600 page = find_lock_page(mapping, index); 1601 if (unlikely(page == NULL)) { 1602 result = SCAN_FAIL; 1603 goto xa_unlocked; 1604 } 1605 } else if (PageDirty(page)) { 1606 /* 1607 * khugepaged only works on read-only fd, 1608 * so this page is dirty because it hasn't 1609 * been flushed since first write. There 1610 * won't be new dirty pages. 1611 * 1612 * Trigger async flush here and hope the 1613 * writeback is done when khugepaged 1614 * revisits this page. 1615 * 1616 * This is a one-off situation. We are not 1617 * forcing writeback in loop. 1618 */ 1619 xas_unlock_irq(&xas); 1620 filemap_flush(mapping); 1621 result = SCAN_FAIL; 1622 goto xa_unlocked; 1623 } else if (trylock_page(page)) { 1624 get_page(page); 1625 xas_unlock_irq(&xas); 1626 } else { 1627 result = SCAN_PAGE_LOCK; 1628 goto xa_locked; 1629 } 1630 } 1631 1632 /* 1633 * The page must be locked, so we can drop the i_pages lock 1634 * without racing with truncate. 1635 */ 1636 VM_BUG_ON_PAGE(!PageLocked(page), page); 1637 1638 /* make sure the page is up to date */ 1639 if (unlikely(!PageUptodate(page))) { 1640 result = SCAN_FAIL; 1641 goto out_unlock; 1642 } 1643 1644 /* 1645 * If file was truncated then extended, or hole-punched, before 1646 * we locked the first page, then a THP might be there already. 1647 */ 1648 if (PageTransCompound(page)) { 1649 result = SCAN_PAGE_COMPOUND; 1650 goto out_unlock; 1651 } 1652 1653 if (page_mapping(page) != mapping) { 1654 result = SCAN_TRUNCATED; 1655 goto out_unlock; 1656 } 1657 1658 if (!is_shmem && PageDirty(page)) { 1659 /* 1660 * khugepaged only works on read-only fd, so this 1661 * page is dirty because it hasn't been flushed 1662 * since first write. 1663 */ 1664 result = SCAN_FAIL; 1665 goto out_unlock; 1666 } 1667 1668 if (isolate_lru_page(page)) { 1669 result = SCAN_DEL_PAGE_LRU; 1670 goto out_unlock; 1671 } 1672 1673 if (page_has_private(page) && 1674 !try_to_release_page(page, GFP_KERNEL)) { 1675 result = SCAN_PAGE_HAS_PRIVATE; 1676 goto out_unlock; 1677 } 1678 1679 if (page_mapped(page)) 1680 unmap_mapping_pages(mapping, index, 1, false); 1681 1682 xas_lock_irq(&xas); 1683 xas_set(&xas, index); 1684 1685 VM_BUG_ON_PAGE(page != xas_load(&xas), page); 1686 VM_BUG_ON_PAGE(page_mapped(page), page); 1687 1688 /* 1689 * The page is expected to have page_count() == 3: 1690 * - we hold a pin on it; 1691 * - one reference from page cache; 1692 * - one from isolate_lru_page; 1693 */ 1694 if (!page_ref_freeze(page, 3)) { 1695 result = SCAN_PAGE_COUNT; 1696 xas_unlock_irq(&xas); 1697 putback_lru_page(page); 1698 goto out_unlock; 1699 } 1700 1701 /* 1702 * Add the page to the list to be able to undo the collapse if 1703 * something go wrong. 1704 */ 1705 list_add_tail(&page->lru, &pagelist); 1706 1707 /* Finally, replace with the new page. */ 1708 xas_store(&xas, new_page); 1709 continue; 1710 out_unlock: 1711 unlock_page(page); 1712 put_page(page); 1713 goto xa_unlocked; 1714 } 1715 1716 if (is_shmem) 1717 __inc_node_page_state(new_page, NR_SHMEM_THPS); 1718 else { 1719 __inc_node_page_state(new_page, NR_FILE_THPS); 1720 filemap_nr_thps_inc(mapping); 1721 } 1722 1723 if (nr_none) { 1724 struct zone *zone = page_zone(new_page); 1725 1726 __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none); 1727 if (is_shmem) 1728 __mod_node_page_state(zone->zone_pgdat, 1729 NR_SHMEM, nr_none); 1730 } 1731 1732 xa_locked: 1733 xas_unlock_irq(&xas); 1734 xa_unlocked: 1735 1736 if (result == SCAN_SUCCEED) { 1737 struct page *page, *tmp; 1738 1739 /* 1740 * Replacing old pages with new one has succeeded, now we 1741 * need to copy the content and free the old pages. 1742 */ 1743 index = start; 1744 list_for_each_entry_safe(page, tmp, &pagelist, lru) { 1745 while (index < page->index) { 1746 clear_highpage(new_page + (index % HPAGE_PMD_NR)); 1747 index++; 1748 } 1749 copy_highpage(new_page + (page->index % HPAGE_PMD_NR), 1750 page); 1751 list_del(&page->lru); 1752 page->mapping = NULL; 1753 page_ref_unfreeze(page, 1); 1754 ClearPageActive(page); 1755 ClearPageUnevictable(page); 1756 unlock_page(page); 1757 put_page(page); 1758 index++; 1759 } 1760 while (index < end) { 1761 clear_highpage(new_page + (index % HPAGE_PMD_NR)); 1762 index++; 1763 } 1764 1765 SetPageUptodate(new_page); 1766 page_ref_add(new_page, HPAGE_PMD_NR - 1); 1767 mem_cgroup_commit_charge(new_page, memcg, false, true); 1768 1769 if (is_shmem) { 1770 set_page_dirty(new_page); 1771 lru_cache_add_anon(new_page); 1772 } else { 1773 lru_cache_add_file(new_page); 1774 } 1775 count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1); 1776 1777 /* 1778 * Remove pte page tables, so we can re-fault the page as huge. 1779 */ 1780 retract_page_tables(mapping, start); 1781 *hpage = NULL; 1782 1783 khugepaged_pages_collapsed++; 1784 } else { 1785 struct page *page; 1786 1787 /* Something went wrong: roll back page cache changes */ 1788 xas_lock_irq(&xas); 1789 mapping->nrpages -= nr_none; 1790 1791 if (is_shmem) 1792 shmem_uncharge(mapping->host, nr_none); 1793 1794 xas_set(&xas, start); 1795 xas_for_each(&xas, page, end - 1) { 1796 page = list_first_entry_or_null(&pagelist, 1797 struct page, lru); 1798 if (!page || xas.xa_index < page->index) { 1799 if (!nr_none) 1800 break; 1801 nr_none--; 1802 /* Put holes back where they were */ 1803 xas_store(&xas, NULL); 1804 continue; 1805 } 1806 1807 VM_BUG_ON_PAGE(page->index != xas.xa_index, page); 1808 1809 /* Unfreeze the page. */ 1810 list_del(&page->lru); 1811 page_ref_unfreeze(page, 2); 1812 xas_store(&xas, page); 1813 xas_pause(&xas); 1814 xas_unlock_irq(&xas); 1815 unlock_page(page); 1816 putback_lru_page(page); 1817 xas_lock_irq(&xas); 1818 } 1819 VM_BUG_ON(nr_none); 1820 xas_unlock_irq(&xas); 1821 1822 mem_cgroup_cancel_charge(new_page, memcg, true); 1823 new_page->mapping = NULL; 1824 } 1825 1826 unlock_page(new_page); 1827 out: 1828 VM_BUG_ON(!list_empty(&pagelist)); 1829 /* TODO: tracepoints */ 1830 } 1831 1832 static void khugepaged_scan_file(struct mm_struct *mm, 1833 struct file *file, pgoff_t start, struct page **hpage) 1834 { 1835 struct page *page = NULL; 1836 struct address_space *mapping = file->f_mapping; 1837 XA_STATE(xas, &mapping->i_pages, start); 1838 int present, swap; 1839 int node = NUMA_NO_NODE; 1840 int result = SCAN_SUCCEED; 1841 1842 present = 0; 1843 swap = 0; 1844 memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load)); 1845 rcu_read_lock(); 1846 xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) { 1847 if (xas_retry(&xas, page)) 1848 continue; 1849 1850 if (xa_is_value(page)) { 1851 if (++swap > khugepaged_max_ptes_swap) { 1852 result = SCAN_EXCEED_SWAP_PTE; 1853 break; 1854 } 1855 continue; 1856 } 1857 1858 if (PageTransCompound(page)) { 1859 result = SCAN_PAGE_COMPOUND; 1860 break; 1861 } 1862 1863 node = page_to_nid(page); 1864 if (khugepaged_scan_abort(node)) { 1865 result = SCAN_SCAN_ABORT; 1866 break; 1867 } 1868 khugepaged_node_load[node]++; 1869 1870 if (!PageLRU(page)) { 1871 result = SCAN_PAGE_LRU; 1872 break; 1873 } 1874 1875 if (page_count(page) != 1876 1 + page_mapcount(page) + page_has_private(page)) { 1877 result = SCAN_PAGE_COUNT; 1878 break; 1879 } 1880 1881 /* 1882 * We probably should check if the page is referenced here, but 1883 * nobody would transfer pte_young() to PageReferenced() for us. 1884 * And rmap walk here is just too costly... 1885 */ 1886 1887 present++; 1888 1889 if (need_resched()) { 1890 xas_pause(&xas); 1891 cond_resched_rcu(); 1892 } 1893 } 1894 rcu_read_unlock(); 1895 1896 if (result == SCAN_SUCCEED) { 1897 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) { 1898 result = SCAN_EXCEED_NONE_PTE; 1899 } else { 1900 node = khugepaged_find_target_node(); 1901 collapse_file(mm, file, start, hpage, node); 1902 } 1903 } 1904 1905 /* TODO: tracepoints */ 1906 } 1907 #else 1908 static void khugepaged_scan_file(struct mm_struct *mm, 1909 struct file *file, pgoff_t start, struct page **hpage) 1910 { 1911 BUILD_BUG(); 1912 } 1913 1914 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot) 1915 { 1916 return 0; 1917 } 1918 #endif 1919 1920 static unsigned int khugepaged_scan_mm_slot(unsigned int pages, 1921 struct page **hpage) 1922 __releases(&khugepaged_mm_lock) 1923 __acquires(&khugepaged_mm_lock) 1924 { 1925 struct mm_slot *mm_slot; 1926 struct mm_struct *mm; 1927 struct vm_area_struct *vma; 1928 int progress = 0; 1929 1930 VM_BUG_ON(!pages); 1931 lockdep_assert_held(&khugepaged_mm_lock); 1932 1933 if (khugepaged_scan.mm_slot) 1934 mm_slot = khugepaged_scan.mm_slot; 1935 else { 1936 mm_slot = list_entry(khugepaged_scan.mm_head.next, 1937 struct mm_slot, mm_node); 1938 khugepaged_scan.address = 0; 1939 khugepaged_scan.mm_slot = mm_slot; 1940 } 1941 spin_unlock(&khugepaged_mm_lock); 1942 khugepaged_collapse_pte_mapped_thps(mm_slot); 1943 1944 mm = mm_slot->mm; 1945 /* 1946 * Don't wait for semaphore (to avoid long wait times). Just move to 1947 * the next mm on the list. 1948 */ 1949 vma = NULL; 1950 if (unlikely(!down_read_trylock(&mm->mmap_sem))) 1951 goto breakouterloop_mmap_sem; 1952 if (likely(!khugepaged_test_exit(mm))) 1953 vma = find_vma(mm, khugepaged_scan.address); 1954 1955 progress++; 1956 for (; vma; vma = vma->vm_next) { 1957 unsigned long hstart, hend; 1958 1959 cond_resched(); 1960 if (unlikely(khugepaged_test_exit(mm))) { 1961 progress++; 1962 break; 1963 } 1964 if (!hugepage_vma_check(vma, vma->vm_flags)) { 1965 skip: 1966 progress++; 1967 continue; 1968 } 1969 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; 1970 hend = vma->vm_end & HPAGE_PMD_MASK; 1971 if (hstart >= hend) 1972 goto skip; 1973 if (khugepaged_scan.address > hend) 1974 goto skip; 1975 if (khugepaged_scan.address < hstart) 1976 khugepaged_scan.address = hstart; 1977 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK); 1978 1979 while (khugepaged_scan.address < hend) { 1980 int ret; 1981 cond_resched(); 1982 if (unlikely(khugepaged_test_exit(mm))) 1983 goto breakouterloop; 1984 1985 VM_BUG_ON(khugepaged_scan.address < hstart || 1986 khugepaged_scan.address + HPAGE_PMD_SIZE > 1987 hend); 1988 if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) { 1989 struct file *file; 1990 pgoff_t pgoff = linear_page_index(vma, 1991 khugepaged_scan.address); 1992 1993 if (shmem_file(vma->vm_file) 1994 && !shmem_huge_enabled(vma)) 1995 goto skip; 1996 file = get_file(vma->vm_file); 1997 up_read(&mm->mmap_sem); 1998 ret = 1; 1999 khugepaged_scan_file(mm, file, pgoff, hpage); 2000 fput(file); 2001 } else { 2002 ret = khugepaged_scan_pmd(mm, vma, 2003 khugepaged_scan.address, 2004 hpage); 2005 } 2006 /* move to next address */ 2007 khugepaged_scan.address += HPAGE_PMD_SIZE; 2008 progress += HPAGE_PMD_NR; 2009 if (ret) 2010 /* we released mmap_sem so break loop */ 2011 goto breakouterloop_mmap_sem; 2012 if (progress >= pages) 2013 goto breakouterloop; 2014 } 2015 } 2016 breakouterloop: 2017 up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */ 2018 breakouterloop_mmap_sem: 2019 2020 spin_lock(&khugepaged_mm_lock); 2021 VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot); 2022 /* 2023 * Release the current mm_slot if this mm is about to die, or 2024 * if we scanned all vmas of this mm. 2025 */ 2026 if (khugepaged_test_exit(mm) || !vma) { 2027 /* 2028 * Make sure that if mm_users is reaching zero while 2029 * khugepaged runs here, khugepaged_exit will find 2030 * mm_slot not pointing to the exiting mm. 2031 */ 2032 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) { 2033 khugepaged_scan.mm_slot = list_entry( 2034 mm_slot->mm_node.next, 2035 struct mm_slot, mm_node); 2036 khugepaged_scan.address = 0; 2037 } else { 2038 khugepaged_scan.mm_slot = NULL; 2039 khugepaged_full_scans++; 2040 } 2041 2042 collect_mm_slot(mm_slot); 2043 } 2044 2045 return progress; 2046 } 2047 2048 static int khugepaged_has_work(void) 2049 { 2050 return !list_empty(&khugepaged_scan.mm_head) && 2051 khugepaged_enabled(); 2052 } 2053 2054 static int khugepaged_wait_event(void) 2055 { 2056 return !list_empty(&khugepaged_scan.mm_head) || 2057 kthread_should_stop(); 2058 } 2059 2060 static void khugepaged_do_scan(void) 2061 { 2062 struct page *hpage = NULL; 2063 unsigned int progress = 0, pass_through_head = 0; 2064 unsigned int pages = khugepaged_pages_to_scan; 2065 bool wait = true; 2066 2067 barrier(); /* write khugepaged_pages_to_scan to local stack */ 2068 2069 while (progress < pages) { 2070 if (!khugepaged_prealloc_page(&hpage, &wait)) 2071 break; 2072 2073 cond_resched(); 2074 2075 if (unlikely(kthread_should_stop() || try_to_freeze())) 2076 break; 2077 2078 spin_lock(&khugepaged_mm_lock); 2079 if (!khugepaged_scan.mm_slot) 2080 pass_through_head++; 2081 if (khugepaged_has_work() && 2082 pass_through_head < 2) 2083 progress += khugepaged_scan_mm_slot(pages - progress, 2084 &hpage); 2085 else 2086 progress = pages; 2087 spin_unlock(&khugepaged_mm_lock); 2088 } 2089 2090 if (!IS_ERR_OR_NULL(hpage)) 2091 put_page(hpage); 2092 } 2093 2094 static bool khugepaged_should_wakeup(void) 2095 { 2096 return kthread_should_stop() || 2097 time_after_eq(jiffies, khugepaged_sleep_expire); 2098 } 2099 2100 static void khugepaged_wait_work(void) 2101 { 2102 if (khugepaged_has_work()) { 2103 const unsigned long scan_sleep_jiffies = 2104 msecs_to_jiffies(khugepaged_scan_sleep_millisecs); 2105 2106 if (!scan_sleep_jiffies) 2107 return; 2108 2109 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies; 2110 wait_event_freezable_timeout(khugepaged_wait, 2111 khugepaged_should_wakeup(), 2112 scan_sleep_jiffies); 2113 return; 2114 } 2115 2116 if (khugepaged_enabled()) 2117 wait_event_freezable(khugepaged_wait, khugepaged_wait_event()); 2118 } 2119 2120 static int khugepaged(void *none) 2121 { 2122 struct mm_slot *mm_slot; 2123 2124 set_freezable(); 2125 set_user_nice(current, MAX_NICE); 2126 2127 while (!kthread_should_stop()) { 2128 khugepaged_do_scan(); 2129 khugepaged_wait_work(); 2130 } 2131 2132 spin_lock(&khugepaged_mm_lock); 2133 mm_slot = khugepaged_scan.mm_slot; 2134 khugepaged_scan.mm_slot = NULL; 2135 if (mm_slot) 2136 collect_mm_slot(mm_slot); 2137 spin_unlock(&khugepaged_mm_lock); 2138 return 0; 2139 } 2140 2141 static void set_recommended_min_free_kbytes(void) 2142 { 2143 struct zone *zone; 2144 int nr_zones = 0; 2145 unsigned long recommended_min; 2146 2147 for_each_populated_zone(zone) { 2148 /* 2149 * We don't need to worry about fragmentation of 2150 * ZONE_MOVABLE since it only has movable pages. 2151 */ 2152 if (zone_idx(zone) > gfp_zone(GFP_USER)) 2153 continue; 2154 2155 nr_zones++; 2156 } 2157 2158 /* Ensure 2 pageblocks are free to assist fragmentation avoidance */ 2159 recommended_min = pageblock_nr_pages * nr_zones * 2; 2160 2161 /* 2162 * Make sure that on average at least two pageblocks are almost free 2163 * of another type, one for a migratetype to fall back to and a 2164 * second to avoid subsequent fallbacks of other types There are 3 2165 * MIGRATE_TYPES we care about. 2166 */ 2167 recommended_min += pageblock_nr_pages * nr_zones * 2168 MIGRATE_PCPTYPES * MIGRATE_PCPTYPES; 2169 2170 /* don't ever allow to reserve more than 5% of the lowmem */ 2171 recommended_min = min(recommended_min, 2172 (unsigned long) nr_free_buffer_pages() / 20); 2173 recommended_min <<= (PAGE_SHIFT-10); 2174 2175 if (recommended_min > min_free_kbytes) { 2176 if (user_min_free_kbytes >= 0) 2177 pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n", 2178 min_free_kbytes, recommended_min); 2179 2180 min_free_kbytes = recommended_min; 2181 } 2182 setup_per_zone_wmarks(); 2183 } 2184 2185 int start_stop_khugepaged(void) 2186 { 2187 static struct task_struct *khugepaged_thread __read_mostly; 2188 static DEFINE_MUTEX(khugepaged_mutex); 2189 int err = 0; 2190 2191 mutex_lock(&khugepaged_mutex); 2192 if (khugepaged_enabled()) { 2193 if (!khugepaged_thread) 2194 khugepaged_thread = kthread_run(khugepaged, NULL, 2195 "khugepaged"); 2196 if (IS_ERR(khugepaged_thread)) { 2197 pr_err("khugepaged: kthread_run(khugepaged) failed\n"); 2198 err = PTR_ERR(khugepaged_thread); 2199 khugepaged_thread = NULL; 2200 goto fail; 2201 } 2202 2203 if (!list_empty(&khugepaged_scan.mm_head)) 2204 wake_up_interruptible(&khugepaged_wait); 2205 2206 set_recommended_min_free_kbytes(); 2207 } else if (khugepaged_thread) { 2208 kthread_stop(khugepaged_thread); 2209 khugepaged_thread = NULL; 2210 } 2211 fail: 2212 mutex_unlock(&khugepaged_mutex); 2213 return err; 2214 } 2215