1# SPDX-License-Identifier: GPL-2.0-only 2 3menu "Memory Management options" 4 5# 6# For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can 7# add proper SWAP support to them, in which case this can be remove. 8# 9config ARCH_NO_SWAP 10 bool 11 12menuconfig SWAP 13 bool "Support for paging of anonymous memory (swap)" 14 depends on MMU && BLOCK && !ARCH_NO_SWAP 15 default y 16 help 17 This option allows you to choose whether you want to have support 18 for so called swap devices or swap files in your kernel that are 19 used to provide more virtual memory than the actual RAM present 20 in your computer. If unsure say Y. 21 22config ZSWAP 23 bool "Compressed cache for swap pages" 24 depends on SWAP 25 select CRYPTO 26 select ZSMALLOC 27 help 28 A lightweight compressed cache for swap pages. It takes 29 pages that are in the process of being swapped out and attempts to 30 compress them into a dynamically allocated RAM-based memory pool. 31 This can result in a significant I/O reduction on swap device and, 32 in the case where decompressing from RAM is faster than swap device 33 reads, can also improve workload performance. 34 35config ZSWAP_DEFAULT_ON 36 bool "Enable the compressed cache for swap pages by default" 37 depends on ZSWAP 38 help 39 If selected, the compressed cache for swap pages will be enabled 40 at boot, otherwise it will be disabled. 41 42 The selection made here can be overridden by using the kernel 43 command line 'zswap.enabled=' option. 44 45config ZSWAP_SHRINKER_DEFAULT_ON 46 bool "Shrink the zswap pool on memory pressure" 47 depends on ZSWAP 48 default n 49 help 50 If selected, the zswap shrinker will be enabled, and the pages 51 stored in the zswap pool will become available for reclaim (i.e 52 written back to the backing swap device) on memory pressure. 53 54 This means that zswap writeback could happen even if the pool is 55 not yet full, or the cgroup zswap limit has not been reached, 56 reducing the chance that cold pages will reside in the zswap pool 57 and consume memory indefinitely. 58 59choice 60 prompt "Default compressor" 61 depends on ZSWAP 62 default ZSWAP_COMPRESSOR_DEFAULT_LZO 63 help 64 Selects the default compression algorithm for the compressed cache 65 for swap pages. 66 67 For an overview what kind of performance can be expected from 68 a particular compression algorithm please refer to the benchmarks 69 available at the following LWN page: 70 https://lwn.net/Articles/751795/ 71 72 If in doubt, select 'LZO'. 73 74 The selection made here can be overridden by using the kernel 75 command line 'zswap.compressor=' option. 76 77config ZSWAP_COMPRESSOR_DEFAULT_DEFLATE 78 bool "Deflate" 79 select CRYPTO_DEFLATE 80 help 81 Use the Deflate algorithm as the default compression algorithm. 82 83config ZSWAP_COMPRESSOR_DEFAULT_LZO 84 bool "LZO" 85 select CRYPTO_LZO 86 help 87 Use the LZO algorithm as the default compression algorithm. 88 89config ZSWAP_COMPRESSOR_DEFAULT_842 90 bool "842" 91 select CRYPTO_842 92 help 93 Use the 842 algorithm as the default compression algorithm. 94 95config ZSWAP_COMPRESSOR_DEFAULT_LZ4 96 bool "LZ4" 97 select CRYPTO_LZ4 98 help 99 Use the LZ4 algorithm as the default compression algorithm. 100 101config ZSWAP_COMPRESSOR_DEFAULT_LZ4HC 102 bool "LZ4HC" 103 select CRYPTO_LZ4HC 104 help 105 Use the LZ4HC algorithm as the default compression algorithm. 106 107config ZSWAP_COMPRESSOR_DEFAULT_ZSTD 108 bool "zstd" 109 select CRYPTO_ZSTD 110 help 111 Use the zstd algorithm as the default compression algorithm. 112endchoice 113 114config ZSWAP_COMPRESSOR_DEFAULT 115 string 116 depends on ZSWAP 117 default "deflate" if ZSWAP_COMPRESSOR_DEFAULT_DEFLATE 118 default "lzo" if ZSWAP_COMPRESSOR_DEFAULT_LZO 119 default "842" if ZSWAP_COMPRESSOR_DEFAULT_842 120 default "lz4" if ZSWAP_COMPRESSOR_DEFAULT_LZ4 121 default "lz4hc" if ZSWAP_COMPRESSOR_DEFAULT_LZ4HC 122 default "zstd" if ZSWAP_COMPRESSOR_DEFAULT_ZSTD 123 default "" 124 125config ZSMALLOC 126 tristate 127 128if ZSMALLOC 129 130menu "Zsmalloc allocator options" 131 depends on ZSMALLOC 132 133comment "Zsmalloc is a common backend allocator for zswap & zram" 134 135config ZSMALLOC_STAT 136 bool "Export zsmalloc statistics" 137 select DEBUG_FS 138 help 139 This option enables code in the zsmalloc to collect various 140 statistics about what's happening in zsmalloc and exports that 141 information to userspace via debugfs. 142 If unsure, say N. 143 144config ZSMALLOC_CHAIN_SIZE 145 int "Maximum number of physical pages per-zspage" 146 default 8 147 range 4 16 148 help 149 This option sets the upper limit on the number of physical pages 150 that a zmalloc page (zspage) can consist of. The optimal zspage 151 chain size is calculated for each size class during the 152 initialization of the pool. 153 154 Changing this option can alter the characteristics of size classes, 155 such as the number of pages per zspage and the number of objects 156 per zspage. This can also result in different configurations of 157 the pool, as zsmalloc merges size classes with similar 158 characteristics. 159 160 For more information, see zsmalloc documentation. 161 162endmenu 163 164endif 165 166menu "Slab allocator options" 167 168config SLUB 169 def_bool y 170 171config KVFREE_RCU_BATCHED 172 def_bool y 173 depends on !SLUB_TINY && !TINY_RCU 174 175config SLUB_TINY 176 bool "Configure for minimal memory footprint" 177 depends on EXPERT && !COMPILE_TEST 178 select SLAB_MERGE_DEFAULT 179 help 180 Configures the slab allocator in a way to achieve minimal memory 181 footprint, sacrificing scalability, debugging and other features. 182 This is intended only for the smallest system that had used the 183 SLOB allocator and is not recommended for systems with more than 184 16MB RAM. 185 186 If unsure, say N. 187 188config SLAB_MERGE_DEFAULT 189 bool "Allow slab caches to be merged" 190 default y 191 help 192 For reduced kernel memory fragmentation, slab caches can be 193 merged when they share the same size and other characteristics. 194 This carries a risk of kernel heap overflows being able to 195 overwrite objects from merged caches (and more easily control 196 cache layout), which makes such heap attacks easier to exploit 197 by attackers. By keeping caches unmerged, these kinds of exploits 198 can usually only damage objects in the same cache. To disable 199 merging at runtime, "slab_nomerge" can be passed on the kernel 200 command line. 201 202config SLAB_FREELIST_RANDOM 203 bool "Randomize slab freelist" 204 depends on !SLUB_TINY 205 help 206 Randomizes the freelist order used on creating new pages. This 207 security feature reduces the predictability of the kernel slab 208 allocator against heap overflows. 209 210config SLAB_FREELIST_HARDENED 211 bool "Harden slab freelist metadata" 212 depends on !SLUB_TINY 213 help 214 Many kernel heap attacks try to target slab cache metadata and 215 other infrastructure. This options makes minor performance 216 sacrifices to harden the kernel slab allocator against common 217 freelist exploit methods. 218 219config SLAB_BUCKETS 220 bool "Support allocation from separate kmalloc buckets" 221 depends on !SLUB_TINY 222 default SLAB_FREELIST_HARDENED 223 help 224 Kernel heap attacks frequently depend on being able to create 225 specifically-sized allocations with user-controlled contents 226 that will be allocated into the same kmalloc bucket as a 227 target object. To avoid sharing these allocation buckets, 228 provide an explicitly separated set of buckets to be used for 229 user-controlled allocations. This may very slightly increase 230 memory fragmentation, though in practice it's only a handful 231 of extra pages since the bulk of user-controlled allocations 232 are relatively long-lived. 233 234 If unsure, say Y. 235 236config SLUB_STATS 237 default n 238 bool "Enable performance statistics" 239 depends on SYSFS && !SLUB_TINY 240 help 241 The statistics are useful to debug slab allocation behavior in 242 order find ways to optimize the allocator. This should never be 243 enabled for production use since keeping statistics slows down 244 the allocator by a few percentage points. The slabinfo command 245 supports the determination of the most active slabs to figure 246 out which slabs are relevant to a particular load. 247 Try running: slabinfo -DA 248 249config SLUB_CPU_PARTIAL 250 default y 251 depends on SMP && !SLUB_TINY 252 bool "Enable per cpu partial caches" 253 help 254 Per cpu partial caches accelerate objects allocation and freeing 255 that is local to a processor at the price of more indeterminism 256 in the latency of the free. On overflow these caches will be cleared 257 which requires the taking of locks that may cause latency spikes. 258 Typically one would choose no for a realtime system. 259 260config RANDOM_KMALLOC_CACHES 261 default n 262 depends on !SLUB_TINY 263 bool "Randomize slab caches for normal kmalloc" 264 help 265 A hardening feature that creates multiple copies of slab caches for 266 normal kmalloc allocation and makes kmalloc randomly pick one based 267 on code address, which makes the attackers more difficult to spray 268 vulnerable memory objects on the heap for the purpose of exploiting 269 memory vulnerabilities. 270 271 Currently the number of copies is set to 16, a reasonably large value 272 that effectively diverges the memory objects allocated for different 273 subsystems or modules into different caches, at the expense of a 274 limited degree of memory and CPU overhead that relates to hardware and 275 system workload. 276 277endmenu # Slab allocator options 278 279config SHUFFLE_PAGE_ALLOCATOR 280 bool "Page allocator randomization" 281 default SLAB_FREELIST_RANDOM && ACPI_NUMA 282 help 283 Randomization of the page allocator improves the average 284 utilization of a direct-mapped memory-side-cache. See section 285 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI 286 6.2a specification for an example of how a platform advertises 287 the presence of a memory-side-cache. There are also incidental 288 security benefits as it reduces the predictability of page 289 allocations to compliment SLAB_FREELIST_RANDOM, but the 290 default granularity of shuffling on the MAX_PAGE_ORDER i.e, 10th 291 order of pages is selected based on cache utilization benefits 292 on x86. 293 294 While the randomization improves cache utilization it may 295 negatively impact workloads on platforms without a cache. For 296 this reason, by default, the randomization is not enabled even 297 if SHUFFLE_PAGE_ALLOCATOR=y. The randomization may be force enabled 298 with the 'page_alloc.shuffle' kernel command line parameter. 299 300 Say Y if unsure. 301 302config COMPAT_BRK 303 bool "Disable heap randomization" 304 default y 305 help 306 Randomizing heap placement makes heap exploits harder, but it 307 also breaks ancient binaries (including anything libc5 based). 308 This option changes the bootup default to heap randomization 309 disabled, and can be overridden at runtime by setting 310 /proc/sys/kernel/randomize_va_space to 2. 311 312 On non-ancient distros (post-2000 ones) N is usually a safe choice. 313 314config MMAP_ALLOW_UNINITIALIZED 315 bool "Allow mmapped anonymous memory to be uninitialized" 316 depends on EXPERT && !MMU 317 default n 318 help 319 Normally, and according to the Linux spec, anonymous memory obtained 320 from mmap() has its contents cleared before it is passed to 321 userspace. Enabling this config option allows you to request that 322 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus 323 providing a huge performance boost. If this option is not enabled, 324 then the flag will be ignored. 325 326 This is taken advantage of by uClibc's malloc(), and also by 327 ELF-FDPIC binfmt's brk and stack allocator. 328 329 Because of the obvious security issues, this option should only be 330 enabled on embedded devices where you control what is run in 331 userspace. Since that isn't generally a problem on no-MMU systems, 332 it is normally safe to say Y here. 333 334 See Documentation/admin-guide/mm/nommu-mmap.rst for more information. 335 336config SELECT_MEMORY_MODEL 337 def_bool y 338 depends on ARCH_SELECT_MEMORY_MODEL 339 340choice 341 prompt "Memory model" 342 depends on SELECT_MEMORY_MODEL 343 default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT 344 default FLATMEM_MANUAL 345 help 346 This option allows you to change some of the ways that 347 Linux manages its memory internally. Most users will 348 only have one option here selected by the architecture 349 configuration. This is normal. 350 351config FLATMEM_MANUAL 352 bool "Flat Memory" 353 depends on !ARCH_SPARSEMEM_ENABLE || ARCH_FLATMEM_ENABLE 354 help 355 This option is best suited for non-NUMA systems with 356 flat address space. The FLATMEM is the most efficient 357 system in terms of performance and resource consumption 358 and it is the best option for smaller systems. 359 360 For systems that have holes in their physical address 361 spaces and for features like NUMA and memory hotplug, 362 choose "Sparse Memory". 363 364 If unsure, choose this option (Flat Memory) over any other. 365 366config SPARSEMEM_MANUAL 367 bool "Sparse Memory" 368 depends on ARCH_SPARSEMEM_ENABLE 369 help 370 This will be the only option for some systems, including 371 memory hot-plug systems. This is normal. 372 373 This option provides efficient support for systems with 374 holes is their physical address space and allows memory 375 hot-plug and hot-remove. 376 377 If unsure, choose "Flat Memory" over this option. 378 379endchoice 380 381config SPARSEMEM 382 def_bool y 383 depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL 384 385config FLATMEM 386 def_bool y 387 depends on !SPARSEMEM || FLATMEM_MANUAL 388 389# 390# SPARSEMEM_EXTREME (which is the default) does some bootmem 391# allocations when sparse_init() is called. If this cannot 392# be done on your architecture, select this option. However, 393# statically allocating the mem_section[] array can potentially 394# consume vast quantities of .bss, so be careful. 395# 396# This option will also potentially produce smaller runtime code 397# with gcc 3.4 and later. 398# 399config SPARSEMEM_STATIC 400 bool 401 402# 403# Architecture platforms which require a two level mem_section in SPARSEMEM 404# must select this option. This is usually for architecture platforms with 405# an extremely sparse physical address space. 406# 407config SPARSEMEM_EXTREME 408 def_bool y 409 depends on SPARSEMEM && !SPARSEMEM_STATIC 410 411config SPARSEMEM_VMEMMAP_ENABLE 412 bool 413 414config SPARSEMEM_VMEMMAP 415 def_bool y 416 depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE 417 help 418 SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise 419 pfn_to_page and page_to_pfn operations. This is the most 420 efficient option when sufficient kernel resources are available. 421 422config SPARSEMEM_VMEMMAP_PREINIT 423 bool 424# 425# Select this config option from the architecture Kconfig, if it is preferred 426# to enable the feature of HugeTLB/dev_dax vmemmap optimization. 427# 428config ARCH_WANT_OPTIMIZE_DAX_VMEMMAP 429 bool 430 431config ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP 432 bool 433 434config ARCH_WANT_HUGETLB_VMEMMAP_PREINIT 435 bool 436 437config HAVE_MEMBLOCK_PHYS_MAP 438 bool 439 440config HAVE_GUP_FAST 441 depends on MMU 442 bool 443 444# Enable memblock support for scratch memory which is needed for kexec handover 445config MEMBLOCK_KHO_SCRATCH 446 bool 447 448# Don't discard allocated memory used to track "memory" and "reserved" memblocks 449# after early boot, so it can still be used to test for validity of memory. 450# Also, memblocks are updated with memory hot(un)plug. 451config ARCH_KEEP_MEMBLOCK 452 bool 453 454# Keep arch NUMA mapping infrastructure post-init. 455config NUMA_KEEP_MEMINFO 456 bool 457 458config MEMORY_ISOLATION 459 bool 460 461# IORESOURCE_SYSTEM_RAM regions in the kernel resource tree that are marked 462# IORESOURCE_EXCLUSIVE cannot be mapped to user space, for example, via 463# /dev/mem. 464config EXCLUSIVE_SYSTEM_RAM 465 def_bool y 466 depends on !DEVMEM || STRICT_DEVMEM 467 468# 469# Only be set on architectures that have completely implemented memory hotplug 470# feature. If you are not sure, don't touch it. 471# 472config HAVE_BOOTMEM_INFO_NODE 473 def_bool n 474 475config ARCH_ENABLE_MEMORY_HOTPLUG 476 bool 477 478config ARCH_ENABLE_MEMORY_HOTREMOVE 479 bool 480 481# eventually, we can have this option just 'select SPARSEMEM' 482menuconfig MEMORY_HOTPLUG 483 bool "Memory hotplug" 484 select MEMORY_ISOLATION 485 depends on SPARSEMEM 486 depends on ARCH_ENABLE_MEMORY_HOTPLUG 487 depends on 64BIT 488 select NUMA_KEEP_MEMINFO if NUMA 489 490if MEMORY_HOTPLUG 491 492choice 493 prompt "Memory Hotplug Default Online Type" 494 default MHP_DEFAULT_ONLINE_TYPE_OFFLINE 495 help 496 Default memory type for hotplugged memory. 497 498 This option sets the default policy setting for memory hotplug 499 onlining policy (/sys/devices/system/memory/auto_online_blocks) which 500 determines what happens to newly added memory regions. Policy setting 501 can always be changed at runtime. 502 503 The default is 'offline'. 504 505 Select offline to defer onlining to drivers and user policy. 506 Select auto to let the kernel choose what zones to utilize. 507 Select online_kernel to generally allow kernel usage of this memory. 508 Select online_movable to generally disallow kernel usage of this memory. 509 510 Example kernel usage would be page structs and page tables. 511 512 See Documentation/admin-guide/mm/memory-hotplug.rst for more information. 513 514config MHP_DEFAULT_ONLINE_TYPE_OFFLINE 515 bool "offline" 516 help 517 Hotplugged memory will not be onlined by default. 518 Choose this for systems with drivers and user policy that 519 handle onlining of hotplug memory policy. 520 521config MHP_DEFAULT_ONLINE_TYPE_ONLINE_AUTO 522 bool "auto" 523 help 524 Select this if you want the kernel to automatically online 525 hotplugged memory into the zone it thinks is reasonable. 526 This memory may be utilized for kernel data. 527 528config MHP_DEFAULT_ONLINE_TYPE_ONLINE_KERNEL 529 bool "kernel" 530 help 531 Select this if you want the kernel to automatically online 532 hotplugged memory into a zone capable of being used for kernel 533 data. This typically means ZONE_NORMAL. 534 535config MHP_DEFAULT_ONLINE_TYPE_ONLINE_MOVABLE 536 bool "movable" 537 help 538 Select this if you want the kernel to automatically online 539 hotplug memory into ZONE_MOVABLE. This memory will generally 540 not be utilized for kernel data. 541 542 This should only be used when the admin knows sufficient 543 ZONE_NORMAL memory is available to describe hotplug memory, 544 otherwise hotplug memory may fail to online. For example, 545 sufficient kernel-capable memory (ZONE_NORMAL) must be 546 available to allocate page structs to describe ZONE_MOVABLE. 547 548endchoice 549 550config MEMORY_HOTREMOVE 551 bool "Allow for memory hot remove" 552 select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64) 553 depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE 554 depends on MIGRATION 555 556config MHP_MEMMAP_ON_MEMORY 557 def_bool y 558 depends on MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP 559 depends on ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE 560 561endif # MEMORY_HOTPLUG 562 563config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE 564 bool 565 566# Heavily threaded applications may benefit from splitting the mm-wide 567# page_table_lock, so that faults on different parts of the user address 568# space can be handled with less contention: split it at this NR_CPUS. 569# Default to 4 for wider testing, though 8 might be more appropriate. 570# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock. 571# PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes. 572# SPARC32 allocates multiple pte tables within a single page, and therefore 573# a per-page lock leads to problems when multiple tables need to be locked 574# at the same time (e.g. copy_page_range()). 575# DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page. 576# 577config SPLIT_PTE_PTLOCKS 578 def_bool y 579 depends on MMU 580 depends on SMP 581 depends on NR_CPUS >= 4 582 depends on !ARM || CPU_CACHE_VIPT 583 depends on !PARISC || PA20 584 depends on !SPARC32 585 586config ARCH_ENABLE_SPLIT_PMD_PTLOCK 587 bool 588 589config SPLIT_PMD_PTLOCKS 590 def_bool y 591 depends on SPLIT_PTE_PTLOCKS && ARCH_ENABLE_SPLIT_PMD_PTLOCK 592 593# 594# support for memory balloon 595config MEMORY_BALLOON 596 bool 597 598# 599# support for memory balloon compaction 600config BALLOON_COMPACTION 601 bool "Allow for balloon memory compaction/migration" 602 default y 603 depends on COMPACTION && MEMORY_BALLOON 604 help 605 Memory fragmentation introduced by ballooning might reduce 606 significantly the number of 2MB contiguous memory blocks that can be 607 used within a guest, thus imposing performance penalties associated 608 with the reduced number of transparent huge pages that could be used 609 by the guest workload. Allowing the compaction & migration for memory 610 pages enlisted as being part of memory balloon devices avoids the 611 scenario aforementioned and helps improving memory defragmentation. 612 613# 614# support for memory compaction 615config COMPACTION 616 bool "Allow for memory compaction" 617 default y 618 select MIGRATION 619 depends on MMU 620 help 621 Compaction is the only memory management component to form 622 high order (larger physically contiguous) memory blocks 623 reliably. The page allocator relies on compaction heavily and 624 the lack of the feature can lead to unexpected OOM killer 625 invocations for high order memory requests. You shouldn't 626 disable this option unless there really is a strong reason for 627 it and then we would be really interested to hear about that at 628 linux-mm@kvack.org. 629 630config COMPACT_UNEVICTABLE_DEFAULT 631 int 632 depends on COMPACTION 633 default 0 if PREEMPT_RT 634 default 1 635 636# 637# support for free page reporting 638config PAGE_REPORTING 639 bool "Free page reporting" 640 help 641 Free page reporting allows for the incremental acquisition of 642 free pages from the buddy allocator for the purpose of reporting 643 those pages to another entity, such as a hypervisor, so that the 644 memory can be freed within the host for other uses. 645 646# 647# support for page migration 648# 649config MIGRATION 650 bool "Page migration" 651 default y 652 depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU 653 help 654 Allows the migration of the physical location of pages of processes 655 while the virtual addresses are not changed. This is useful in 656 two situations. The first is on NUMA systems to put pages nearer 657 to the processors accessing. The second is when allocating huge 658 pages as migration can relocate pages to satisfy a huge page 659 allocation instead of reclaiming. 660 661config DEVICE_MIGRATION 662 def_bool MIGRATION && ZONE_DEVICE 663 664config ARCH_ENABLE_HUGEPAGE_MIGRATION 665 bool 666 667config ARCH_ENABLE_THP_MIGRATION 668 bool 669 670config HUGETLB_PAGE_SIZE_VARIABLE 671 def_bool n 672 help 673 Allows the pageblock_order value to be dynamic instead of just standard 674 HUGETLB_PAGE_ORDER when there are multiple HugeTLB page sizes available 675 on a platform. 676 677 Note that the pageblock_order cannot exceed MAX_PAGE_ORDER and will be 678 clamped down to MAX_PAGE_ORDER. 679 680config CONTIG_ALLOC 681 def_bool (MEMORY_ISOLATION && COMPACTION) || CMA 682 683config PCP_BATCH_SCALE_MAX 684 int "Maximum scale factor of PCP (Per-CPU pageset) batch allocate/free" 685 default 5 686 range 0 6 687 help 688 In page allocator, PCP (Per-CPU pageset) is refilled and drained in 689 batches. The batch number is scaled automatically to improve page 690 allocation/free throughput. But too large scale factor may hurt 691 latency. This option sets the upper limit of scale factor to limit 692 the maximum latency. 693 694config PHYS_ADDR_T_64BIT 695 def_bool 64BIT 696 697config BOUNCE 698 bool "Enable bounce buffers" 699 default y 700 depends on BLOCK && MMU && HIGHMEM 701 help 702 Enable bounce buffers for devices that cannot access the full range of 703 memory available to the CPU. Enabled by default when HIGHMEM is 704 selected, but you may say n to override this. 705 706config MMU_NOTIFIER 707 bool 708 select INTERVAL_TREE 709 710config KSM 711 bool "Enable KSM for page merging" 712 depends on MMU 713 select XXHASH 714 help 715 Enable Kernel Samepage Merging: KSM periodically scans those areas 716 of an application's address space that an app has advised may be 717 mergeable. When it finds pages of identical content, it replaces 718 the many instances by a single page with that content, so 719 saving memory until one or another app needs to modify the content. 720 Recommended for use with KVM, or with other duplicative applications. 721 See Documentation/mm/ksm.rst for more information: KSM is inactive 722 until a program has madvised that an area is MADV_MERGEABLE, and 723 root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set). 724 725config DEFAULT_MMAP_MIN_ADDR 726 int "Low address space to protect from user allocation" 727 depends on MMU 728 default 4096 729 help 730 This is the portion of low virtual memory which should be protected 731 from userspace allocation. Keeping a user from writing to low pages 732 can help reduce the impact of kernel NULL pointer bugs. 733 734 For most arm64, ppc64 and x86 users with lots of address space 735 a value of 65536 is reasonable and should cause no problems. 736 On arm and other archs it should not be higher than 32768. 737 Programs which use vm86 functionality or have some need to map 738 this low address space will need CAP_SYS_RAWIO or disable this 739 protection by setting the value to 0. 740 741 This value can be changed after boot using the 742 /proc/sys/vm/mmap_min_addr tunable. 743 744config ARCH_SUPPORTS_MEMORY_FAILURE 745 bool 746 747config MEMORY_FAILURE 748 depends on MMU 749 depends on ARCH_SUPPORTS_MEMORY_FAILURE 750 bool "Enable recovery from hardware memory errors" 751 select MEMORY_ISOLATION 752 select RAS 753 help 754 Enables code to recover from some memory failures on systems 755 with MCA recovery. This allows a system to continue running 756 even when some of its memory has uncorrected errors. This requires 757 special hardware support and typically ECC memory. 758 759config HWPOISON_INJECT 760 tristate "HWPoison pages injector" 761 depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS 762 select PROC_PAGE_MONITOR 763 764config NOMMU_INITIAL_TRIM_EXCESS 765 int "Turn on mmap() excess space trimming before booting" 766 depends on !MMU 767 default 1 768 help 769 The NOMMU mmap() frequently needs to allocate large contiguous chunks 770 of memory on which to store mappings, but it can only ask the system 771 allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently 772 more than it requires. To deal with this, mmap() is able to trim off 773 the excess and return it to the allocator. 774 775 If trimming is enabled, the excess is trimmed off and returned to the 776 system allocator, which can cause extra fragmentation, particularly 777 if there are a lot of transient processes. 778 779 If trimming is disabled, the excess is kept, but not used, which for 780 long-term mappings means that the space is wasted. 781 782 Trimming can be dynamically controlled through a sysctl option 783 (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of 784 excess pages there must be before trimming should occur, or zero if 785 no trimming is to occur. 786 787 This option specifies the initial value of this option. The default 788 of 1 says that all excess pages should be trimmed. 789 790 See Documentation/admin-guide/mm/nommu-mmap.rst for more information. 791 792config ARCH_WANT_GENERAL_HUGETLB 793 bool 794 795config ARCH_WANTS_THP_SWAP 796 def_bool n 797 798config PERSISTENT_HUGE_ZERO_FOLIO 799 bool "Allocate a PMD sized folio for zeroing" 800 depends on TRANSPARENT_HUGEPAGE 801 help 802 Enable this option to reduce the runtime refcounting overhead 803 of the huge zero folio and expand the places in the kernel 804 that can use huge zero folios. For instance, block I/O benefits 805 from access to large folios for zeroing memory. 806 807 With this option enabled, the huge zero folio is allocated 808 once and never freed. One full huge page's worth of memory shall 809 be used. 810 811 Say Y if your system has lots of memory. Say N if you are 812 memory constrained. 813 814config MM_ID 815 def_bool n 816 817menuconfig TRANSPARENT_HUGEPAGE 818 bool "Transparent Hugepage Support" 819 depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE && !PREEMPT_RT 820 select COMPACTION 821 select XARRAY_MULTI 822 select MM_ID 823 help 824 Transparent Hugepages allows the kernel to use huge pages and 825 huge tlb transparently to the applications whenever possible. 826 This feature can improve computing performance to certain 827 applications by speeding up page faults during memory 828 allocation, by reducing the number of tlb misses and by speeding 829 up the pagetable walking. 830 831 If memory constrained on embedded, you may want to say N. 832 833if TRANSPARENT_HUGEPAGE 834 835choice 836 prompt "Transparent Hugepage Support sysfs defaults" 837 depends on TRANSPARENT_HUGEPAGE 838 default TRANSPARENT_HUGEPAGE_ALWAYS 839 help 840 Selects the sysfs defaults for Transparent Hugepage Support. 841 842 config TRANSPARENT_HUGEPAGE_ALWAYS 843 bool "always" 844 help 845 Enabling Transparent Hugepage always, can increase the 846 memory footprint of applications without a guaranteed 847 benefit but it will work automatically for all applications. 848 849 config TRANSPARENT_HUGEPAGE_MADVISE 850 bool "madvise" 851 help 852 Enabling Transparent Hugepage madvise, will only provide a 853 performance improvement benefit to the applications using 854 madvise(MADV_HUGEPAGE) but it won't risk to increase the 855 memory footprint of applications without a guaranteed 856 benefit. 857 858 config TRANSPARENT_HUGEPAGE_NEVER 859 bool "never" 860 help 861 Disable Transparent Hugepage by default. It can still be 862 enabled at runtime via sysfs. 863endchoice 864 865config THP_SWAP 866 def_bool y 867 depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP && 64BIT 868 help 869 Swap transparent huge pages in one piece, without splitting. 870 XXX: For now, swap cluster backing transparent huge page 871 will be split after swapout. 872 873 For selection by architectures with reasonable THP sizes. 874 875config READ_ONLY_THP_FOR_FS 876 bool "Read-only THP for filesystems (EXPERIMENTAL)" 877 depends on TRANSPARENT_HUGEPAGE 878 879 help 880 Allow khugepaged to put read-only file-backed pages in THP. 881 882 This is marked experimental because it is a new feature. Write 883 support of file THPs will be developed in the next few release 884 cycles. 885 886config NO_PAGE_MAPCOUNT 887 bool "No per-page mapcount (EXPERIMENTAL)" 888 help 889 Do not maintain per-page mapcounts for pages part of larger 890 allocations, such as transparent huge pages. 891 892 When this config option is enabled, some interfaces that relied on 893 this information will rely on less-precise per-allocation information 894 instead: for example, using the average per-page mapcount in such 895 a large allocation instead of the per-page mapcount. 896 897 EXPERIMENTAL because the impact of some changes is still unclear. 898 899endif # TRANSPARENT_HUGEPAGE 900 901# simple helper to make the code a bit easier to read 902config PAGE_MAPCOUNT 903 def_bool !NO_PAGE_MAPCOUNT 904 905# 906# The architecture supports pgtable leaves that is larger than PAGE_SIZE 907# 908config PGTABLE_HAS_HUGE_LEAVES 909 def_bool TRANSPARENT_HUGEPAGE || HUGETLB_PAGE 910 911# TODO: Allow to be enabled without THP 912config ARCH_SUPPORTS_HUGE_PFNMAP 913 def_bool n 914 depends on TRANSPARENT_HUGEPAGE 915 916config ARCH_SUPPORTS_PMD_PFNMAP 917 def_bool y 918 depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE 919 920config ARCH_SUPPORTS_PUD_PFNMAP 921 def_bool y 922 depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD 923 924# 925# Architectures that always use weak definitions for percpu 926# variables in modules should set this. 927# 928config ARCH_MODULE_NEEDS_WEAK_PER_CPU 929 bool 930 931# 932# UP and nommu archs use km based percpu allocator 933# 934config NEED_PER_CPU_KM 935 depends on !SMP || !MMU 936 bool 937 default y 938 939config NEED_PER_CPU_EMBED_FIRST_CHUNK 940 bool 941 942config NEED_PER_CPU_PAGE_FIRST_CHUNK 943 bool 944 945config USE_PERCPU_NUMA_NODE_ID 946 bool 947 948config HAVE_SETUP_PER_CPU_AREA 949 bool 950 951config CMA 952 bool "Contiguous Memory Allocator" 953 depends on MMU 954 select MIGRATION 955 select MEMORY_ISOLATION 956 help 957 This enables the Contiguous Memory Allocator which allows other 958 subsystems to allocate big physically-contiguous blocks of memory. 959 CMA reserves a region of memory and allows only movable pages to 960 be allocated from it. This way, the kernel can use the memory for 961 pagecache and when a subsystem requests for contiguous area, the 962 allocated pages are migrated away to serve the contiguous request. 963 964 If unsure, say "n". 965 966config CMA_DEBUGFS 967 bool "CMA debugfs interface" 968 depends on CMA && DEBUG_FS 969 help 970 Turns on the DebugFS interface for CMA. 971 972config CMA_SYSFS 973 bool "CMA information through sysfs interface" 974 depends on CMA && SYSFS 975 help 976 This option exposes some sysfs attributes to get information 977 from CMA. 978 979config CMA_AREAS 980 int "Maximum count of the CMA areas" 981 depends on CMA 982 default 20 if NUMA 983 default 8 984 help 985 CMA allows to create CMA areas for particular purpose, mainly, 986 used as device private area. This parameter sets the maximum 987 number of CMA area in the system. 988 989 If unsure, leave the default value "8" in UMA and "20" in NUMA. 990 991# 992# Select this config option from the architecture Kconfig, if available, to set 993# the max page order for physically contiguous allocations. 994# 995config ARCH_FORCE_MAX_ORDER 996 int 997 998# 999# When ARCH_FORCE_MAX_ORDER is not defined, 1000# the default page block order is MAX_PAGE_ORDER (10) as per 1001# include/linux/mmzone.h. 1002# 1003config PAGE_BLOCK_MAX_ORDER 1004 int "Page Block Order Upper Limit" 1005 range 1 10 if ARCH_FORCE_MAX_ORDER = 0 1006 default 10 if ARCH_FORCE_MAX_ORDER = 0 1007 range 1 ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER != 0 1008 default ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER != 0 1009 help 1010 The page block order refers to the power of two number of pages that 1011 are physically contiguous and can have a migrate type associated to 1012 them. The maximum size of the page block order is at least limited by 1013 ARCH_FORCE_MAX_ORDER/MAX_PAGE_ORDER. 1014 1015 This config adds a new upper limit of default page block 1016 order when the page block order is required to be smaller than 1017 ARCH_FORCE_MAX_ORDER/MAX_PAGE_ORDER or other limits 1018 (see include/linux/pageblock-flags.h for details). 1019 1020 Reducing pageblock order can negatively impact THP generation 1021 success rate. If your workloads use THP heavily, please use this 1022 option with caution. 1023 1024 Don't change if unsure. 1025 1026config MEM_SOFT_DIRTY 1027 bool "Track memory changes" 1028 depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS 1029 select PROC_PAGE_MONITOR 1030 help 1031 This option enables memory changes tracking by introducing a 1032 soft-dirty bit on pte-s. This bit it set when someone writes 1033 into a page just as regular dirty bit, but unlike the latter 1034 it can be cleared by hands. 1035 1036 See Documentation/admin-guide/mm/soft-dirty.rst for more details. 1037 1038config GENERIC_EARLY_IOREMAP 1039 bool 1040 1041config STACK_MAX_DEFAULT_SIZE_MB 1042 int "Default maximum user stack size for 32-bit processes (MB)" 1043 default 100 1044 range 8 2048 1045 depends on STACK_GROWSUP && (!64BIT || COMPAT) 1046 help 1047 This is the maximum stack size in Megabytes in the VM layout of 32-bit 1048 user processes when the stack grows upwards (currently only on parisc 1049 arch) when the RLIMIT_STACK hard limit is unlimited. 1050 1051 A sane initial value is 100 MB. 1052 1053config DEFERRED_STRUCT_PAGE_INIT 1054 bool "Defer initialisation of struct pages to kthreads" 1055 depends on SPARSEMEM 1056 depends on !NEED_PER_CPU_KM 1057 depends on 64BIT 1058 depends on !KMSAN 1059 select PADATA 1060 help 1061 Ordinarily all struct pages are initialised during early boot in a 1062 single thread. On very large machines this can take a considerable 1063 amount of time. If this option is set, large machines will bring up 1064 a subset of memmap at boot and then initialise the rest in parallel. 1065 This has a potential performance impact on tasks running early in the 1066 lifetime of the system until these kthreads finish the 1067 initialisation. 1068 1069config PAGE_IDLE_FLAG 1070 bool 1071 select PAGE_EXTENSION if !64BIT 1072 help 1073 This adds PG_idle and PG_young flags to 'struct page'. PTE Accessed 1074 bit writers can set the state of the bit in the flags so that PTE 1075 Accessed bit readers may avoid disturbance. 1076 1077config IDLE_PAGE_TRACKING 1078 bool "Enable idle page tracking" 1079 depends on SYSFS && MMU 1080 select PAGE_IDLE_FLAG 1081 help 1082 This feature allows to estimate the amount of user pages that have 1083 not been touched during a given period of time. This information can 1084 be useful to tune memory cgroup limits and/or for job placement 1085 within a compute cluster. 1086 1087 See Documentation/admin-guide/mm/idle_page_tracking.rst for 1088 more details. 1089 1090# Architectures which implement cpu_dcache_is_aliasing() to query 1091# whether the data caches are aliased (VIVT or VIPT with dcache 1092# aliasing) need to select this. 1093config ARCH_HAS_CPU_CACHE_ALIASING 1094 bool 1095 1096config ARCH_HAS_CACHE_LINE_SIZE 1097 bool 1098 1099config ARCH_HAS_CURRENT_STACK_POINTER 1100 bool 1101 help 1102 In support of HARDENED_USERCOPY performing stack variable lifetime 1103 checking, an architecture-agnostic way to find the stack pointer 1104 is needed. Once an architecture defines an unsigned long global 1105 register alias named "current_stack_pointer", this config can be 1106 selected. 1107 1108config ARCH_HAS_ZONE_DMA_SET 1109 bool 1110 1111config ZONE_DMA 1112 bool "Support DMA zone" if ARCH_HAS_ZONE_DMA_SET 1113 default y if ARM64 || X86 1114 1115config ZONE_DMA32 1116 bool "Support DMA32 zone" if ARCH_HAS_ZONE_DMA_SET 1117 depends on !X86_32 1118 default y if ARM64 1119 1120config ZONE_DEVICE 1121 bool "Device memory (pmem, HMM, etc...) hotplug support" 1122 depends on MEMORY_HOTPLUG 1123 depends on MEMORY_HOTREMOVE 1124 depends on SPARSEMEM_VMEMMAP 1125 select XARRAY_MULTI 1126 1127 help 1128 Device memory hotplug support allows for establishing pmem, 1129 or other device driver discovered memory regions, in the 1130 memmap. This allows pfn_to_page() lookups of otherwise 1131 "device-physical" addresses which is needed for using a DAX 1132 mapping in an O_DIRECT operation, among other things. 1133 1134 If FS_DAX is enabled, then say Y. 1135 1136# 1137# Helpers to mirror range of the CPU page tables of a process into device page 1138# tables. 1139# 1140config HMM_MIRROR 1141 bool 1142 depends on MMU 1143 1144config GET_FREE_REGION 1145 bool 1146 1147config DEVICE_PRIVATE 1148 bool "Unaddressable device memory (GPU memory, ...)" 1149 depends on ZONE_DEVICE 1150 select GET_FREE_REGION 1151 1152 help 1153 Allows creation of struct pages to represent unaddressable device 1154 memory; i.e., memory that is only accessible from the device (or 1155 group of devices). You likely also want to select HMM_MIRROR. 1156 1157config VMAP_PFN 1158 bool 1159 1160config ARCH_USES_HIGH_VMA_FLAGS 1161 bool 1162config ARCH_HAS_PKEYS 1163 bool 1164 1165config ARCH_USES_PG_ARCH_2 1166 bool 1167config ARCH_USES_PG_ARCH_3 1168 bool 1169 1170config VM_EVENT_COUNTERS 1171 default y 1172 bool "Enable VM event counters for /proc/vmstat" if EXPERT 1173 help 1174 VM event counters are needed for event counts to be shown. 1175 This option allows the disabling of the VM event counters 1176 on EXPERT systems. /proc/vmstat will only show page counts 1177 if VM event counters are disabled. 1178 1179config PERCPU_STATS 1180 bool "Collect percpu memory statistics" 1181 help 1182 This feature collects and exposes statistics via debugfs. The 1183 information includes global and per chunk statistics, which can 1184 be used to help understand percpu memory usage. 1185 1186config GUP_TEST 1187 bool "Enable infrastructure for get_user_pages()-related unit tests" 1188 depends on DEBUG_FS 1189 help 1190 Provides /sys/kernel/debug/gup_test, which in turn provides a way 1191 to make ioctl calls that can launch kernel-based unit tests for 1192 the get_user_pages*() and pin_user_pages*() family of API calls. 1193 1194 These tests include benchmark testing of the _fast variants of 1195 get_user_pages*() and pin_user_pages*(), as well as smoke tests of 1196 the non-_fast variants. 1197 1198 There is also a sub-test that allows running dump_page() on any 1199 of up to eight pages (selected by command line args) within the 1200 range of user-space addresses. These pages are either pinned via 1201 pin_user_pages*(), or pinned via get_user_pages*(), as specified 1202 by other command line arguments. 1203 1204 See tools/testing/selftests/mm/gup_test.c 1205 1206comment "GUP_TEST needs to have DEBUG_FS enabled" 1207 depends on !GUP_TEST && !DEBUG_FS 1208 1209config GUP_GET_PXX_LOW_HIGH 1210 bool 1211 1212config DMAPOOL_TEST 1213 tristate "Enable a module to run time tests on dma_pool" 1214 depends on HAS_DMA 1215 help 1216 Provides a test module that will allocate and free many blocks of 1217 various sizes and report how long it takes. This is intended to 1218 provide a consistent way to measure how changes to the 1219 dma_pool_alloc/free routines affect performance. 1220 1221config ARCH_HAS_PTE_SPECIAL 1222 bool 1223 1224config MAPPING_DIRTY_HELPERS 1225 bool 1226 1227config KMAP_LOCAL 1228 bool 1229 1230config KMAP_LOCAL_NON_LINEAR_PTE_ARRAY 1231 bool 1232 1233config MEMFD_CREATE 1234 bool "Enable memfd_create() system call" if EXPERT 1235 1236config SECRETMEM 1237 default y 1238 bool "Enable memfd_secret() system call" if EXPERT 1239 depends on ARCH_HAS_SET_DIRECT_MAP 1240 help 1241 Enable the memfd_secret() system call with the ability to create 1242 memory areas visible only in the context of the owning process and 1243 not mapped to other processes and other kernel page tables. 1244 1245config ANON_VMA_NAME 1246 bool "Anonymous VMA name support" 1247 depends on PROC_FS && ADVISE_SYSCALLS && MMU 1248 1249 help 1250 Allow naming anonymous virtual memory areas. 1251 1252 This feature allows assigning names to virtual memory areas. Assigned 1253 names can be later retrieved from /proc/pid/maps and /proc/pid/smaps 1254 and help identifying individual anonymous memory areas. 1255 Assigning a name to anonymous virtual memory area might prevent that 1256 area from being merged with adjacent virtual memory areas due to the 1257 difference in their name. 1258 1259config HAVE_ARCH_USERFAULTFD_WP 1260 bool 1261 help 1262 Arch has userfaultfd write protection support 1263 1264config HAVE_ARCH_USERFAULTFD_MINOR 1265 bool 1266 help 1267 Arch has userfaultfd minor fault support 1268 1269menuconfig USERFAULTFD 1270 bool "Enable userfaultfd() system call" 1271 depends on MMU 1272 help 1273 Enable the userfaultfd() system call that allows to intercept and 1274 handle page faults in userland. 1275 1276if USERFAULTFD 1277config PTE_MARKER_UFFD_WP 1278 bool "Userfaultfd write protection support for shmem/hugetlbfs" 1279 default y 1280 depends on HAVE_ARCH_USERFAULTFD_WP 1281 1282 help 1283 Allows to create marker PTEs for userfaultfd write protection 1284 purposes. It is required to enable userfaultfd write protection on 1285 file-backed memory types like shmem and hugetlbfs. 1286endif # USERFAULTFD 1287 1288# multi-gen LRU { 1289config LRU_GEN 1290 bool "Multi-Gen LRU" 1291 depends on MMU 1292 # make sure folio->flags has enough spare bits 1293 depends on 64BIT || !SPARSEMEM || SPARSEMEM_VMEMMAP 1294 help 1295 A high performance LRU implementation to overcommit memory. See 1296 Documentation/admin-guide/mm/multigen_lru.rst for details. 1297 1298config LRU_GEN_ENABLED 1299 bool "Enable by default" 1300 depends on LRU_GEN 1301 help 1302 This option enables the multi-gen LRU by default. 1303 1304config LRU_GEN_STATS 1305 bool "Full stats for debugging" 1306 depends on LRU_GEN 1307 help 1308 Do not enable this option unless you plan to look at historical stats 1309 from evicted generations for debugging purpose. 1310 1311 This option has a per-memcg and per-node memory overhead. 1312 1313config LRU_GEN_WALKS_MMU 1314 def_bool y 1315 depends on LRU_GEN && ARCH_HAS_HW_PTE_YOUNG 1316# } 1317 1318config ARCH_SUPPORTS_PER_VMA_LOCK 1319 def_bool n 1320 1321config PER_VMA_LOCK 1322 def_bool y 1323 depends on ARCH_SUPPORTS_PER_VMA_LOCK && MMU && SMP 1324 help 1325 Allow per-vma locking during page fault handling. 1326 1327 This feature allows locking each virtual memory area separately when 1328 handling page faults instead of taking mmap_lock. 1329 1330config LOCK_MM_AND_FIND_VMA 1331 bool 1332 depends on !STACK_GROWSUP 1333 1334config IOMMU_MM_DATA 1335 bool 1336 1337config EXECMEM 1338 bool 1339 1340config NUMA_MEMBLKS 1341 bool 1342 1343config NUMA_EMU 1344 bool "NUMA emulation" 1345 depends on NUMA_MEMBLKS 1346 depends on X86 || GENERIC_ARCH_NUMA 1347 help 1348 Enable NUMA emulation. A flat machine will be split 1349 into virtual nodes when booted with "numa=fake=N", where N is the 1350 number of nodes. This is only useful for debugging. 1351 1352config ARCH_HAS_USER_SHADOW_STACK 1353 bool 1354 help 1355 The architecture has hardware support for userspace shadow call 1356 stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss). 1357 1358config ARCH_SUPPORTS_PT_RECLAIM 1359 def_bool n 1360 1361config PT_RECLAIM 1362 bool "reclaim empty user page table pages" 1363 default y 1364 depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP 1365 select MMU_GATHER_RCU_TABLE_FREE 1366 help 1367 Try to reclaim empty user page table pages in paths other than munmap 1368 and exit_mmap path. 1369 1370 Note: now only empty user PTE page table pages will be reclaimed. 1371 1372config FIND_NORMAL_PAGE 1373 def_bool n 1374 1375source "mm/damon/Kconfig" 1376 1377endmenu 1378