1 # SPDX-License-Identifier: GPL-2.0-only
3 menu "Memory Management options"
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.
16 bool "Support for paging of anonymous memory (swap)"
17 depends on MMU && BLOCK && !ARCH_NO_SWAP
20 This option allows you to choose whether you want to have support
21 for so called swap devices or swap files in your kernel that are
22 used to provide more virtual memory than the actual RAM present
23 in your computer. If unsure say Y.
26 bool "Compressed cache for swap pages"
31 A lightweight compressed cache for swap pages. It takes
32 pages that are in the process of being swapped out and attempts to
33 compress them into a dynamically allocated RAM-based memory pool.
34 This can result in a significant I/O reduction on swap device and,
35 in the case where decompressing from RAM is faster than swap device
36 reads, can also improve workload performance.
38 config ZSWAP_DEFAULT_ON
39 bool "Enable the compressed cache for swap pages by default"
42 If selected, the compressed cache for swap pages will be enabled
43 at boot, otherwise it will be disabled.
45 The selection made here can be overridden by using the kernel
46 command line 'zswap.enabled=' option.
48 config ZSWAP_SHRINKER_DEFAULT_ON
49 bool "Shrink the zswap pool on memory pressure"
53 If selected, the zswap shrinker will be enabled, and the pages
54 stored in the zswap pool will become available for reclaim (i.e
55 written back to the backing swap device) on memory pressure.
57 This means that zswap writeback could happen even if the pool is
58 not yet full, or the cgroup zswap limit has not been reached,
59 reducing the chance that cold pages will reside in the zswap pool
60 and consume memory indefinitely.
63 prompt "Default compressor"
65 default ZSWAP_COMPRESSOR_DEFAULT_LZO
67 Selects the default compression algorithm for the compressed cache
70 For an overview what kind of performance can be expected from
71 a particular compression algorithm please refer to the benchmarks
72 available at the following LWN page:
73 https://lwn.net/Articles/751795/
75 If in doubt, select 'LZO'.
77 The selection made here can be overridden by using the kernel
78 command line 'zswap.compressor=' option.
80 config ZSWAP_COMPRESSOR_DEFAULT_DEFLATE
84 Use the Deflate algorithm as the default compression algorithm.
86 config ZSWAP_COMPRESSOR_DEFAULT_LZO
90 Use the LZO algorithm as the default compression algorithm.
92 config ZSWAP_COMPRESSOR_DEFAULT_842
96 Use the 842 algorithm as the default compression algorithm.
98 config ZSWAP_COMPRESSOR_DEFAULT_LZ4
102 Use the LZ4 algorithm as the default compression algorithm.
104 config ZSWAP_COMPRESSOR_DEFAULT_LZ4HC
108 Use the LZ4HC algorithm as the default compression algorithm.
110 config ZSWAP_COMPRESSOR_DEFAULT_ZSTD
114 Use the zstd algorithm as the default compression algorithm.
117 config ZSWAP_COMPRESSOR_DEFAULT
120 default "deflate" if ZSWAP_COMPRESSOR_DEFAULT_DEFLATE
121 default "lzo" if ZSWAP_COMPRESSOR_DEFAULT_LZO
122 default "842" if ZSWAP_COMPRESSOR_DEFAULT_842
123 default "lz4" if ZSWAP_COMPRESSOR_DEFAULT_LZ4
124 default "lz4hc" if ZSWAP_COMPRESSOR_DEFAULT_LZ4HC
125 default "zstd" if ZSWAP_COMPRESSOR_DEFAULT_ZSTD
129 prompt "Default allocator"
131 default ZSWAP_ZPOOL_DEFAULT_ZSMALLOC if MMU
132 default ZSWAP_ZPOOL_DEFAULT_ZBUD
134 Selects the default allocator for the compressed cache for
136 The default is 'zbud' for compatibility, however please do
137 read the description of each of the allocators below before
138 making a right choice.
140 The selection made here can be overridden by using the kernel
141 command line 'zswap.zpool=' option.
143 config ZSWAP_ZPOOL_DEFAULT_ZBUD
147 Use the zbud allocator as the default allocator.
149 config ZSWAP_ZPOOL_DEFAULT_Z3FOLD
153 Use the z3fold allocator as the default allocator.
155 config ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
159 Use the zsmalloc allocator as the default allocator.
162 config ZSWAP_ZPOOL_DEFAULT
165 default "zbud" if ZSWAP_ZPOOL_DEFAULT_ZBUD
166 default "z3fold" if ZSWAP_ZPOOL_DEFAULT_Z3FOLD
167 default "zsmalloc" if ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
171 tristate "2:1 compression allocator (zbud)"
174 A special purpose allocator for storing compressed pages.
175 It is designed to store up to two compressed pages per physical
176 page. While this design limits storage density, it has simple and
177 deterministic reclaim properties that make it preferable to a higher
178 density approach when reclaim will be used.
181 tristate "3:1 compression allocator (z3fold)"
184 A special purpose allocator for storing compressed pages.
185 It is designed to store up to three compressed pages per physical
186 page. It is a ZBUD derivative so the simplicity and determinism are
191 prompt "N:1 compression allocator (zsmalloc)" if ZSWAP
194 zsmalloc is a slab-based memory allocator designed to store
195 pages of various compression levels efficiently. It achieves
196 the highest storage density with the least amount of fragmentation.
199 bool "Export zsmalloc statistics"
203 This option enables code in the zsmalloc to collect various
204 statistics about what's happening in zsmalloc and exports that
205 information to userspace via debugfs.
208 config ZSMALLOC_CHAIN_SIZE
209 int "Maximum number of physical pages per-zspage"
214 This option sets the upper limit on the number of physical pages
215 that a zmalloc page (zspage) can consist of. The optimal zspage
216 chain size is calculated for each size class during the
217 initialization of the pool.
219 Changing this option can alter the characteristics of size classes,
220 such as the number of pages per zspage and the number of objects
221 per zspage. This can also result in different configurations of
222 the pool, as zsmalloc merges size classes with similar
225 For more information, see zsmalloc documentation.
227 menu "Slab allocator options"
233 bool "Configure for minimal memory footprint"
235 select SLAB_MERGE_DEFAULT
237 Configures the slab allocator in a way to achieve minimal memory
238 footprint, sacrificing scalability, debugging and other features.
239 This is intended only for the smallest system that had used the
240 SLOB allocator and is not recommended for systems with more than
245 config SLAB_MERGE_DEFAULT
246 bool "Allow slab caches to be merged"
249 For reduced kernel memory fragmentation, slab caches can be
250 merged when they share the same size and other characteristics.
251 This carries a risk of kernel heap overflows being able to
252 overwrite objects from merged caches (and more easily control
253 cache layout), which makes such heap attacks easier to exploit
254 by attackers. By keeping caches unmerged, these kinds of exploits
255 can usually only damage objects in the same cache. To disable
256 merging at runtime, "slab_nomerge" can be passed on the kernel
259 config SLAB_FREELIST_RANDOM
260 bool "Randomize slab freelist"
261 depends on !SLUB_TINY
263 Randomizes the freelist order used on creating new pages. This
264 security feature reduces the predictability of the kernel slab
265 allocator against heap overflows.
267 config SLAB_FREELIST_HARDENED
268 bool "Harden slab freelist metadata"
269 depends on !SLUB_TINY
271 Many kernel heap attacks try to target slab cache metadata and
272 other infrastructure. This options makes minor performance
273 sacrifices to harden the kernel slab allocator against common
274 freelist exploit methods.
278 bool "Enable performance statistics"
279 depends on SYSFS && !SLUB_TINY
281 The statistics are useful to debug slab allocation behavior in
282 order find ways to optimize the allocator. This should never be
283 enabled for production use since keeping statistics slows down
284 the allocator by a few percentage points. The slabinfo command
285 supports the determination of the most active slabs to figure
286 out which slabs are relevant to a particular load.
287 Try running: slabinfo -DA
289 config SLUB_CPU_PARTIAL
291 depends on SMP && !SLUB_TINY
292 bool "Enable per cpu partial caches"
294 Per cpu partial caches accelerate objects allocation and freeing
295 that is local to a processor at the price of more indeterminism
296 in the latency of the free. On overflow these caches will be cleared
297 which requires the taking of locks that may cause latency spikes.
298 Typically one would choose no for a realtime system.
300 config RANDOM_KMALLOC_CACHES
302 depends on !SLUB_TINY
303 bool "Randomize slab caches for normal kmalloc"
305 A hardening feature that creates multiple copies of slab caches for
306 normal kmalloc allocation and makes kmalloc randomly pick one based
307 on code address, which makes the attackers more difficult to spray
308 vulnerable memory objects on the heap for the purpose of exploiting
309 memory vulnerabilities.
311 Currently the number of copies is set to 16, a reasonably large value
312 that effectively diverges the memory objects allocated for different
313 subsystems or modules into different caches, at the expense of a
314 limited degree of memory and CPU overhead that relates to hardware and
317 endmenu # Slab allocator options
319 config SHUFFLE_PAGE_ALLOCATOR
320 bool "Page allocator randomization"
321 default SLAB_FREELIST_RANDOM && ACPI_NUMA
323 Randomization of the page allocator improves the average
324 utilization of a direct-mapped memory-side-cache. See section
325 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI
326 6.2a specification for an example of how a platform advertises
327 the presence of a memory-side-cache. There are also incidental
328 security benefits as it reduces the predictability of page
329 allocations to compliment SLAB_FREELIST_RANDOM, but the
330 default granularity of shuffling on the MAX_PAGE_ORDER i.e, 10th
331 order of pages is selected based on cache utilization benefits
334 While the randomization improves cache utilization it may
335 negatively impact workloads on platforms without a cache. For
336 this reason, by default, the randomization is enabled only
337 after runtime detection of a direct-mapped memory-side-cache.
338 Otherwise, the randomization may be force enabled with the
339 'page_alloc.shuffle' kernel command line parameter.
344 bool "Disable heap randomization"
347 Randomizing heap placement makes heap exploits harder, but it
348 also breaks ancient binaries (including anything libc5 based).
349 This option changes the bootup default to heap randomization
350 disabled, and can be overridden at runtime by setting
351 /proc/sys/kernel/randomize_va_space to 2.
353 On non-ancient distros (post-2000 ones) N is usually a safe choice.
355 config MMAP_ALLOW_UNINITIALIZED
356 bool "Allow mmapped anonymous memory to be uninitialized"
357 depends on EXPERT && !MMU
360 Normally, and according to the Linux spec, anonymous memory obtained
361 from mmap() has its contents cleared before it is passed to
362 userspace. Enabling this config option allows you to request that
363 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
364 providing a huge performance boost. If this option is not enabled,
365 then the flag will be ignored.
367 This is taken advantage of by uClibc's malloc(), and also by
368 ELF-FDPIC binfmt's brk and stack allocator.
370 Because of the obvious security issues, this option should only be
371 enabled on embedded devices where you control what is run in
372 userspace. Since that isn't generally a problem on no-MMU systems,
373 it is normally safe to say Y here.
375 See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
377 config SELECT_MEMORY_MODEL
379 depends on ARCH_SELECT_MEMORY_MODEL
382 prompt "Memory model"
383 depends on SELECT_MEMORY_MODEL
384 default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
385 default FLATMEM_MANUAL
387 This option allows you to change some of the ways that
388 Linux manages its memory internally. Most users will
389 only have one option here selected by the architecture
390 configuration. This is normal.
392 config FLATMEM_MANUAL
394 depends on !ARCH_SPARSEMEM_ENABLE || ARCH_FLATMEM_ENABLE
396 This option is best suited for non-NUMA systems with
397 flat address space. The FLATMEM is the most efficient
398 system in terms of performance and resource consumption
399 and it is the best option for smaller systems.
401 For systems that have holes in their physical address
402 spaces and for features like NUMA and memory hotplug,
403 choose "Sparse Memory".
405 If unsure, choose this option (Flat Memory) over any other.
407 config SPARSEMEM_MANUAL
409 depends on ARCH_SPARSEMEM_ENABLE
411 This will be the only option for some systems, including
412 memory hot-plug systems. This is normal.
414 This option provides efficient support for systems with
415 holes is their physical address space and allows memory
416 hot-plug and hot-remove.
418 If unsure, choose "Flat Memory" over this option.
424 depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
428 depends on !SPARSEMEM || FLATMEM_MANUAL
431 # SPARSEMEM_EXTREME (which is the default) does some bootmem
432 # allocations when sparse_init() is called. If this cannot
433 # be done on your architecture, select this option. However,
434 # statically allocating the mem_section[] array can potentially
435 # consume vast quantities of .bss, so be careful.
437 # This option will also potentially produce smaller runtime code
438 # with gcc 3.4 and later.
440 config SPARSEMEM_STATIC
444 # Architecture platforms which require a two level mem_section in SPARSEMEM
445 # must select this option. This is usually for architecture platforms with
446 # an extremely sparse physical address space.
448 config SPARSEMEM_EXTREME
450 depends on SPARSEMEM && !SPARSEMEM_STATIC
452 config SPARSEMEM_VMEMMAP_ENABLE
455 config SPARSEMEM_VMEMMAP
456 bool "Sparse Memory virtual memmap"
457 depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
460 SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
461 pfn_to_page and page_to_pfn operations. This is the most
462 efficient option when sufficient kernel resources are available.
464 # Select this config option from the architecture Kconfig, if it is preferred
465 # to enable the feature of HugeTLB/dev_dax vmemmap optimization.
467 config ARCH_WANT_OPTIMIZE_DAX_VMEMMAP
470 config ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
473 config HAVE_MEMBLOCK_PHYS_MAP
480 # Don't discard allocated memory used to track "memory" and "reserved" memblocks
481 # after early boot, so it can still be used to test for validity of memory.
482 # Also, memblocks are updated with memory hot(un)plug.
483 config ARCH_KEEP_MEMBLOCK
486 # Keep arch NUMA mapping infrastructure post-init.
487 config NUMA_KEEP_MEMINFO
490 config MEMORY_ISOLATION
493 # IORESOURCE_SYSTEM_RAM regions in the kernel resource tree that are marked
494 # IORESOURCE_EXCLUSIVE cannot be mapped to user space, for example, via
496 config EXCLUSIVE_SYSTEM_RAM
498 depends on !DEVMEM || STRICT_DEVMEM
501 # Only be set on architectures that have completely implemented memory hotplug
502 # feature. If you are not sure, don't touch it.
504 config HAVE_BOOTMEM_INFO_NODE
507 config ARCH_ENABLE_MEMORY_HOTPLUG
510 config ARCH_ENABLE_MEMORY_HOTREMOVE
513 # eventually, we can have this option just 'select SPARSEMEM'
514 menuconfig MEMORY_HOTPLUG
515 bool "Memory hotplug"
516 select MEMORY_ISOLATION
518 depends on ARCH_ENABLE_MEMORY_HOTPLUG
520 select NUMA_KEEP_MEMINFO if NUMA
524 config MEMORY_HOTPLUG_DEFAULT_ONLINE
525 bool "Online the newly added memory blocks by default"
526 depends on MEMORY_HOTPLUG
528 This option sets the default policy setting for memory hotplug
529 onlining policy (/sys/devices/system/memory/auto_online_blocks) which
530 determines what happens to newly added memory regions. Policy setting
531 can always be changed at runtime.
532 See Documentation/admin-guide/mm/memory-hotplug.rst for more information.
534 Say Y here if you want all hot-plugged memory blocks to appear in
535 'online' state by default.
536 Say N here if you want the default policy to keep all hot-plugged
537 memory blocks in 'offline' state.
539 config MEMORY_HOTREMOVE
540 bool "Allow for memory hot remove"
541 select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
542 depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
545 config MHP_MEMMAP_ON_MEMORY
547 depends on MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP
548 depends on ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
550 endif # MEMORY_HOTPLUG
552 config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
555 # Heavily threaded applications may benefit from splitting the mm-wide
556 # page_table_lock, so that faults on different parts of the user address
557 # space can be handled with less contention: split it at this NR_CPUS.
558 # Default to 4 for wider testing, though 8 might be more appropriate.
559 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
560 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
561 # SPARC32 allocates multiple pte tables within a single page, and therefore
562 # a per-page lock leads to problems when multiple tables need to be locked
563 # at the same time (e.g. copy_page_range()).
564 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
566 config SPLIT_PTLOCK_CPUS
568 default "999999" if !MMU
569 default "999999" if ARM && !CPU_CACHE_VIPT
570 default "999999" if PARISC && !PA20
571 default "999999" if SPARC32
574 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
578 # support for memory balloon
579 config MEMORY_BALLOON
583 # support for memory balloon compaction
584 config BALLOON_COMPACTION
585 bool "Allow for balloon memory compaction/migration"
587 depends on COMPACTION && MEMORY_BALLOON
589 Memory fragmentation introduced by ballooning might reduce
590 significantly the number of 2MB contiguous memory blocks that can be
591 used within a guest, thus imposing performance penalties associated
592 with the reduced number of transparent huge pages that could be used
593 by the guest workload. Allowing the compaction & migration for memory
594 pages enlisted as being part of memory balloon devices avoids the
595 scenario aforementioned and helps improving memory defragmentation.
598 # support for memory compaction
600 bool "Allow for memory compaction"
605 Compaction is the only memory management component to form
606 high order (larger physically contiguous) memory blocks
607 reliably. The page allocator relies on compaction heavily and
608 the lack of the feature can lead to unexpected OOM killer
609 invocations for high order memory requests. You shouldn't
610 disable this option unless there really is a strong reason for
611 it and then we would be really interested to hear about that at
614 config COMPACT_UNEVICTABLE_DEFAULT
616 depends on COMPACTION
617 default 0 if PREEMPT_RT
621 # support for free page reporting
622 config PAGE_REPORTING
623 bool "Free page reporting"
626 Free page reporting allows for the incremental acquisition of
627 free pages from the buddy allocator for the purpose of reporting
628 those pages to another entity, such as a hypervisor, so that the
629 memory can be freed within the host for other uses.
632 # support for page migration
635 bool "Page migration"
637 depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
639 Allows the migration of the physical location of pages of processes
640 while the virtual addresses are not changed. This is useful in
641 two situations. The first is on NUMA systems to put pages nearer
642 to the processors accessing. The second is when allocating huge
643 pages as migration can relocate pages to satisfy a huge page
644 allocation instead of reclaiming.
646 config DEVICE_MIGRATION
647 def_bool MIGRATION && ZONE_DEVICE
649 config ARCH_ENABLE_HUGEPAGE_MIGRATION
652 config ARCH_ENABLE_THP_MIGRATION
655 config HUGETLB_PAGE_SIZE_VARIABLE
658 Allows the pageblock_order value to be dynamic instead of just standard
659 HUGETLB_PAGE_ORDER when there are multiple HugeTLB page sizes available
662 Note that the pageblock_order cannot exceed MAX_PAGE_ORDER and will be
663 clamped down to MAX_PAGE_ORDER.
666 def_bool (MEMORY_ISOLATION && COMPACTION) || CMA
668 config PCP_BATCH_SCALE_MAX
669 int "Maximum scale factor of PCP (Per-CPU pageset) batch allocate/free"
673 In page allocator, PCP (Per-CPU pageset) is refilled and drained in
674 batches. The batch number is scaled automatically to improve page
675 allocation/free throughput. But too large scale factor may hurt
676 latency. This option sets the upper limit of scale factor to limit
679 config PHYS_ADDR_T_64BIT
683 bool "Enable bounce buffers"
685 depends on BLOCK && MMU && HIGHMEM
687 Enable bounce buffers for devices that cannot access the full range of
688 memory available to the CPU. Enabled by default when HIGHMEM is
689 selected, but you may say n to override this.
696 bool "Enable KSM for page merging"
700 Enable Kernel Samepage Merging: KSM periodically scans those areas
701 of an application's address space that an app has advised may be
702 mergeable. When it finds pages of identical content, it replaces
703 the many instances by a single page with that content, so
704 saving memory until one or another app needs to modify the content.
705 Recommended for use with KVM, or with other duplicative applications.
706 See Documentation/mm/ksm.rst for more information: KSM is inactive
707 until a program has madvised that an area is MADV_MERGEABLE, and
708 root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
710 config DEFAULT_MMAP_MIN_ADDR
711 int "Low address space to protect from user allocation"
715 This is the portion of low virtual memory which should be protected
716 from userspace allocation. Keeping a user from writing to low pages
717 can help reduce the impact of kernel NULL pointer bugs.
719 For most ppc64 and x86 users with lots of address space
720 a value of 65536 is reasonable and should cause no problems.
721 On arm and other archs it should not be higher than 32768.
722 Programs which use vm86 functionality or have some need to map
723 this low address space will need CAP_SYS_RAWIO or disable this
724 protection by setting the value to 0.
726 This value can be changed after boot using the
727 /proc/sys/vm/mmap_min_addr tunable.
729 config ARCH_SUPPORTS_MEMORY_FAILURE
732 config MEMORY_FAILURE
734 depends on ARCH_SUPPORTS_MEMORY_FAILURE
735 bool "Enable recovery from hardware memory errors"
736 select MEMORY_ISOLATION
739 Enables code to recover from some memory failures on systems
740 with MCA recovery. This allows a system to continue running
741 even when some of its memory has uncorrected errors. This requires
742 special hardware support and typically ECC memory.
744 config HWPOISON_INJECT
745 tristate "HWPoison pages injector"
746 depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
747 select PROC_PAGE_MONITOR
749 config NOMMU_INITIAL_TRIM_EXCESS
750 int "Turn on mmap() excess space trimming before booting"
754 The NOMMU mmap() frequently needs to allocate large contiguous chunks
755 of memory on which to store mappings, but it can only ask the system
756 allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
757 more than it requires. To deal with this, mmap() is able to trim off
758 the excess and return it to the allocator.
760 If trimming is enabled, the excess is trimmed off and returned to the
761 system allocator, which can cause extra fragmentation, particularly
762 if there are a lot of transient processes.
764 If trimming is disabled, the excess is kept, but not used, which for
765 long-term mappings means that the space is wasted.
767 Trimming can be dynamically controlled through a sysctl option
768 (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
769 excess pages there must be before trimming should occur, or zero if
770 no trimming is to occur.
772 This option specifies the initial value of this option. The default
773 of 1 says that all excess pages should be trimmed.
775 See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
777 config ARCH_WANT_GENERAL_HUGETLB
780 config ARCH_WANTS_THP_SWAP
783 menuconfig TRANSPARENT_HUGEPAGE
784 bool "Transparent Hugepage Support"
785 depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE && !PREEMPT_RT
789 Transparent Hugepages allows the kernel to use huge pages and
790 huge tlb transparently to the applications whenever possible.
791 This feature can improve computing performance to certain
792 applications by speeding up page faults during memory
793 allocation, by reducing the number of tlb misses and by speeding
794 up the pagetable walking.
796 If memory constrained on embedded, you may want to say N.
798 if TRANSPARENT_HUGEPAGE
801 prompt "Transparent Hugepage Support sysfs defaults"
802 depends on TRANSPARENT_HUGEPAGE
803 default TRANSPARENT_HUGEPAGE_ALWAYS
805 Selects the sysfs defaults for Transparent Hugepage Support.
807 config TRANSPARENT_HUGEPAGE_ALWAYS
810 Enabling Transparent Hugepage always, can increase the
811 memory footprint of applications without a guaranteed
812 benefit but it will work automatically for all applications.
814 config TRANSPARENT_HUGEPAGE_MADVISE
817 Enabling Transparent Hugepage madvise, will only provide a
818 performance improvement benefit to the applications using
819 madvise(MADV_HUGEPAGE) but it won't risk to increase the
820 memory footprint of applications without a guaranteed
823 config TRANSPARENT_HUGEPAGE_NEVER
826 Disable Transparent Hugepage by default. It can still be
827 enabled at runtime via sysfs.
832 depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP && 64BIT
834 Swap transparent huge pages in one piece, without splitting.
835 XXX: For now, swap cluster backing transparent huge page
836 will be split after swapout.
838 For selection by architectures with reasonable THP sizes.
840 config READ_ONLY_THP_FOR_FS
841 bool "Read-only THP for filesystems (EXPERIMENTAL)"
842 depends on TRANSPARENT_HUGEPAGE && SHMEM
845 Allow khugepaged to put read-only file-backed pages in THP.
847 This is marked experimental because it is a new feature. Write
848 support of file THPs will be developed in the next few release
851 endif # TRANSPARENT_HUGEPAGE
854 # UP and nommu archs use km based percpu allocator
856 config NEED_PER_CPU_KM
857 depends on !SMP || !MMU
861 config NEED_PER_CPU_EMBED_FIRST_CHUNK
864 config NEED_PER_CPU_PAGE_FIRST_CHUNK
867 config USE_PERCPU_NUMA_NODE_ID
870 config HAVE_SETUP_PER_CPU_AREA
874 bool "Contiguous Memory Allocator"
877 select MEMORY_ISOLATION
879 This enables the Contiguous Memory Allocator which allows other
880 subsystems to allocate big physically-contiguous blocks of memory.
881 CMA reserves a region of memory and allows only movable pages to
882 be allocated from it. This way, the kernel can use the memory for
883 pagecache and when a subsystem requests for contiguous area, the
884 allocated pages are migrated away to serve the contiguous request.
889 bool "CMA debugfs interface"
890 depends on CMA && DEBUG_FS
892 Turns on the DebugFS interface for CMA.
895 bool "CMA information through sysfs interface"
896 depends on CMA && SYSFS
898 This option exposes some sysfs attributes to get information
902 int "Maximum count of the CMA areas"
907 CMA allows to create CMA areas for particular purpose, mainly,
908 used as device private area. This parameter sets the maximum
909 number of CMA area in the system.
911 If unsure, leave the default value "8" in UMA and "20" in NUMA.
913 config MEM_SOFT_DIRTY
914 bool "Track memory changes"
915 depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
916 select PROC_PAGE_MONITOR
918 This option enables memory changes tracking by introducing a
919 soft-dirty bit on pte-s. This bit it set when someone writes
920 into a page just as regular dirty bit, but unlike the latter
921 it can be cleared by hands.
923 See Documentation/admin-guide/mm/soft-dirty.rst for more details.
925 config GENERIC_EARLY_IOREMAP
928 config STACK_MAX_DEFAULT_SIZE_MB
929 int "Default maximum user stack size for 32-bit processes (MB)"
932 depends on STACK_GROWSUP && (!64BIT || COMPAT)
934 This is the maximum stack size in Megabytes in the VM layout of 32-bit
935 user processes when the stack grows upwards (currently only on parisc
936 arch) when the RLIMIT_STACK hard limit is unlimited.
938 A sane initial value is 100 MB.
940 config DEFERRED_STRUCT_PAGE_INIT
941 bool "Defer initialisation of struct pages to kthreads"
943 depends on !NEED_PER_CPU_KM
947 Ordinarily all struct pages are initialised during early boot in a
948 single thread. On very large machines this can take a considerable
949 amount of time. If this option is set, large machines will bring up
950 a subset of memmap at boot and then initialise the rest in parallel.
951 This has a potential performance impact on tasks running early in the
952 lifetime of the system until these kthreads finish the
955 config PAGE_IDLE_FLAG
957 select PAGE_EXTENSION if !64BIT
959 This adds PG_idle and PG_young flags to 'struct page'. PTE Accessed
960 bit writers can set the state of the bit in the flags so that PTE
961 Accessed bit readers may avoid disturbance.
963 config IDLE_PAGE_TRACKING
964 bool "Enable idle page tracking"
965 depends on SYSFS && MMU
966 select PAGE_IDLE_FLAG
968 This feature allows to estimate the amount of user pages that have
969 not been touched during a given period of time. This information can
970 be useful to tune memory cgroup limits and/or for job placement
971 within a compute cluster.
973 See Documentation/admin-guide/mm/idle_page_tracking.rst for
976 # Architectures which implement cpu_dcache_is_aliasing() to query
977 # whether the data caches are aliased (VIVT or VIPT with dcache
978 # aliasing) need to select this.
979 config ARCH_HAS_CPU_CACHE_ALIASING
982 config ARCH_HAS_CACHE_LINE_SIZE
985 config ARCH_HAS_CURRENT_STACK_POINTER
988 In support of HARDENED_USERCOPY performing stack variable lifetime
989 checking, an architecture-agnostic way to find the stack pointer
990 is needed. Once an architecture defines an unsigned long global
991 register alias named "current_stack_pointer", this config can be
994 config ARCH_HAS_PTE_DEVMAP
997 config ARCH_HAS_ZONE_DMA_SET
1001 bool "Support DMA zone" if ARCH_HAS_ZONE_DMA_SET
1002 default y if ARM64 || X86
1005 bool "Support DMA32 zone" if ARCH_HAS_ZONE_DMA_SET
1010 bool "Device memory (pmem, HMM, etc...) hotplug support"
1011 depends on MEMORY_HOTPLUG
1012 depends on MEMORY_HOTREMOVE
1013 depends on SPARSEMEM_VMEMMAP
1014 depends on ARCH_HAS_PTE_DEVMAP
1018 Device memory hotplug support allows for establishing pmem,
1019 or other device driver discovered memory regions, in the
1020 memmap. This allows pfn_to_page() lookups of otherwise
1021 "device-physical" addresses which is needed for using a DAX
1022 mapping in an O_DIRECT operation, among other things.
1024 If FS_DAX is enabled, then say Y.
1027 # Helpers to mirror range of the CPU page tables of a process into device page
1034 config GET_FREE_REGION
1035 depends on SPARSEMEM
1038 config DEVICE_PRIVATE
1039 bool "Unaddressable device memory (GPU memory, ...)"
1040 depends on ZONE_DEVICE
1041 select GET_FREE_REGION
1044 Allows creation of struct pages to represent unaddressable device
1045 memory; i.e., memory that is only accessible from the device (or
1046 group of devices). You likely also want to select HMM_MIRROR.
1051 config ARCH_USES_HIGH_VMA_FLAGS
1053 config ARCH_HAS_PKEYS
1056 config ARCH_USES_PG_ARCH_X
1059 Enable the definition of PG_arch_x page flags with x > 1. Only
1060 suitable for 64-bit architectures with CONFIG_FLATMEM or
1061 CONFIG_SPARSEMEM_VMEMMAP enabled, otherwise there may not be
1062 enough room for additional bits in page->flags.
1064 config VM_EVENT_COUNTERS
1066 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1068 VM event counters are needed for event counts to be shown.
1069 This option allows the disabling of the VM event counters
1070 on EXPERT systems. /proc/vmstat will only show page counts
1071 if VM event counters are disabled.
1074 bool "Collect percpu memory statistics"
1076 This feature collects and exposes statistics via debugfs. The
1077 information includes global and per chunk statistics, which can
1078 be used to help understand percpu memory usage.
1081 bool "Enable infrastructure for get_user_pages()-related unit tests"
1084 Provides /sys/kernel/debug/gup_test, which in turn provides a way
1085 to make ioctl calls that can launch kernel-based unit tests for
1086 the get_user_pages*() and pin_user_pages*() family of API calls.
1088 These tests include benchmark testing of the _fast variants of
1089 get_user_pages*() and pin_user_pages*(), as well as smoke tests of
1090 the non-_fast variants.
1092 There is also a sub-test that allows running dump_page() on any
1093 of up to eight pages (selected by command line args) within the
1094 range of user-space addresses. These pages are either pinned via
1095 pin_user_pages*(), or pinned via get_user_pages*(), as specified
1096 by other command line arguments.
1098 See tools/testing/selftests/mm/gup_test.c
1100 comment "GUP_TEST needs to have DEBUG_FS enabled"
1101 depends on !GUP_TEST && !DEBUG_FS
1103 config GUP_GET_PXX_LOW_HIGH
1107 tristate "Enable a module to run time tests on dma_pool"
1110 Provides a test module that will allocate and free many blocks of
1111 various sizes and report how long it takes. This is intended to
1112 provide a consistent way to measure how changes to the
1113 dma_pool_alloc/free routines affect performance.
1115 config ARCH_HAS_PTE_SPECIAL
1119 # Some architectures require a special hugepage directory format that is
1120 # required to support multiple hugepage sizes. For example a4fe3ce76
1121 # "powerpc/mm: Allow more flexible layouts for hugepage pagetables"
1122 # introduced it on powerpc. This allows for a more flexible hugepage
1123 # pagetable layouts.
1125 config ARCH_HAS_HUGEPD
1128 config MAPPING_DIRTY_HELPERS
1134 config KMAP_LOCAL_NON_LINEAR_PTE_ARRAY
1137 # struct io_mapping based helper. Selected by drivers that need them
1142 bool "Enable memfd_create() system call" if EXPERT
1146 bool "Enable memfd_secret() system call" if EXPERT
1147 depends on ARCH_HAS_SET_DIRECT_MAP
1149 Enable the memfd_secret() system call with the ability to create
1150 memory areas visible only in the context of the owning process and
1151 not mapped to other processes and other kernel page tables.
1153 config ANON_VMA_NAME
1154 bool "Anonymous VMA name support"
1155 depends on PROC_FS && ADVISE_SYSCALLS && MMU
1158 Allow naming anonymous virtual memory areas.
1160 This feature allows assigning names to virtual memory areas. Assigned
1161 names can be later retrieved from /proc/pid/maps and /proc/pid/smaps
1162 and help identifying individual anonymous memory areas.
1163 Assigning a name to anonymous virtual memory area might prevent that
1164 area from being merged with adjacent virtual memory areas due to the
1165 difference in their name.
1167 config HAVE_ARCH_USERFAULTFD_WP
1170 Arch has userfaultfd write protection support
1172 config HAVE_ARCH_USERFAULTFD_MINOR
1175 Arch has userfaultfd minor fault support
1177 menuconfig USERFAULTFD
1178 bool "Enable userfaultfd() system call"
1181 Enable the userfaultfd() system call that allows to intercept and
1182 handle page faults in userland.
1185 config PTE_MARKER_UFFD_WP
1186 bool "Userfaultfd write protection support for shmem/hugetlbfs"
1188 depends on HAVE_ARCH_USERFAULTFD_WP
1191 Allows to create marker PTEs for userfaultfd write protection
1192 purposes. It is required to enable userfaultfd write protection on
1193 file-backed memory types like shmem and hugetlbfs.
1198 bool "Multi-Gen LRU"
1200 # make sure folio->flags has enough spare bits
1201 depends on 64BIT || !SPARSEMEM || SPARSEMEM_VMEMMAP
1203 A high performance LRU implementation to overcommit memory. See
1204 Documentation/admin-guide/mm/multigen_lru.rst for details.
1206 config LRU_GEN_ENABLED
1207 bool "Enable by default"
1210 This option enables the multi-gen LRU by default.
1212 config LRU_GEN_STATS
1213 bool "Full stats for debugging"
1216 Do not enable this option unless you plan to look at historical stats
1217 from evicted generations for debugging purpose.
1219 This option has a per-memcg and per-node memory overhead.
1221 config LRU_GEN_WALKS_MMU
1223 depends on LRU_GEN && ARCH_HAS_HW_PTE_YOUNG
1226 config ARCH_SUPPORTS_PER_VMA_LOCK
1231 depends on ARCH_SUPPORTS_PER_VMA_LOCK && MMU && SMP
1233 Allow per-vma locking during page fault handling.
1235 This feature allows locking each virtual memory area separately when
1236 handling page faults instead of taking mmap_lock.
1238 config LOCK_MM_AND_FIND_VMA
1240 depends on !STACK_GROWSUP
1242 config IOMMU_MM_DATA
1245 source "mm/damon/Kconfig"