1 # SPDX-License-Identifier: GPL-2.0-only
3 menu "Memory Management options"
5 config SELECT_MEMORY_MODEL
7 depends on ARCH_SELECT_MEMORY_MODEL
11 depends on SELECT_MEMORY_MODEL
12 default DISCONTIGMEM_MANUAL if ARCH_DISCONTIGMEM_DEFAULT
13 default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
14 default FLATMEM_MANUAL
16 This option allows you to change some of the ways that
17 Linux manages its memory internally. Most users will
18 only have one option here selected by the architecture
19 configuration. This is normal.
23 depends on !(ARCH_DISCONTIGMEM_ENABLE || ARCH_SPARSEMEM_ENABLE) || ARCH_FLATMEM_ENABLE
25 This option is best suited for non-NUMA systems with
26 flat address space. The FLATMEM is the most efficient
27 system in terms of performance and resource consumption
28 and it is the best option for smaller systems.
30 For systems that have holes in their physical address
31 spaces and for features like NUMA and memory hotplug,
32 choose "Sparse Memory".
34 If unsure, choose this option (Flat Memory) over any other.
36 config DISCONTIGMEM_MANUAL
37 bool "Discontiguous Memory"
38 depends on ARCH_DISCONTIGMEM_ENABLE
40 This option provides enhanced support for discontiguous
41 memory systems, over FLATMEM. These systems have holes
42 in their physical address spaces, and this option provides
43 more efficient handling of these holes.
45 Although "Discontiguous Memory" is still used by several
46 architectures, it is considered deprecated in favor of
49 If unsure, choose "Sparse Memory" over this option.
51 config SPARSEMEM_MANUAL
53 depends on ARCH_SPARSEMEM_ENABLE
55 This will be the only option for some systems, including
56 memory hot-plug systems. This is normal.
58 This option provides efficient support for systems with
59 holes is their physical address space and allows memory
60 hot-plug and hot-remove.
62 If unsure, choose "Flat Memory" over this option.
68 depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
72 depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
76 depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
78 config FLAT_NODE_MEM_MAP
83 # Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's
84 # to represent different areas of memory. This variable allows
85 # those dependencies to exist individually.
87 config NEED_MULTIPLE_NODES
89 depends on DISCONTIGMEM || NUMA
91 config HAVE_MEMORY_PRESENT
93 depends on ARCH_HAVE_MEMORY_PRESENT || SPARSEMEM
96 # SPARSEMEM_EXTREME (which is the default) does some bootmem
97 # allocations when memory_present() is called. If this cannot
98 # be done on your architecture, select this option. However,
99 # statically allocating the mem_section[] array can potentially
100 # consume vast quantities of .bss, so be careful.
102 # This option will also potentially produce smaller runtime code
103 # with gcc 3.4 and later.
105 config SPARSEMEM_STATIC
109 # Architecture platforms which require a two level mem_section in SPARSEMEM
110 # must select this option. This is usually for architecture platforms with
111 # an extremely sparse physical address space.
113 config SPARSEMEM_EXTREME
115 depends on SPARSEMEM && !SPARSEMEM_STATIC
117 config SPARSEMEM_VMEMMAP_ENABLE
120 config SPARSEMEM_VMEMMAP
121 bool "Sparse Memory virtual memmap"
122 depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
125 SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
126 pfn_to_page and page_to_pfn operations. This is the most
127 efficient option when sufficient kernel resources are available.
129 config HAVE_MEMBLOCK_NODE_MAP
132 config HAVE_MEMBLOCK_PHYS_MAP
139 config ARCH_KEEP_MEMBLOCK
142 config MEMORY_ISOLATION
146 # Only be set on architectures that have completely implemented memory hotplug
147 # feature. If you are not sure, don't touch it.
149 config HAVE_BOOTMEM_INFO_NODE
152 # eventually, we can have this option just 'select SPARSEMEM'
153 config MEMORY_HOTPLUG
154 bool "Allow for memory hot-add"
155 depends on SPARSEMEM || X86_64_ACPI_NUMA
156 depends on ARCH_ENABLE_MEMORY_HOTPLUG
158 config MEMORY_HOTPLUG_SPARSE
160 depends on SPARSEMEM && MEMORY_HOTPLUG
162 config MEMORY_HOTPLUG_DEFAULT_ONLINE
163 bool "Online the newly added memory blocks by default"
164 depends on MEMORY_HOTPLUG
166 This option sets the default policy setting for memory hotplug
167 onlining policy (/sys/devices/system/memory/auto_online_blocks) which
168 determines what happens to newly added memory regions. Policy setting
169 can always be changed at runtime.
170 See Documentation/admin-guide/mm/memory-hotplug.rst for more information.
172 Say Y here if you want all hot-plugged memory blocks to appear in
173 'online' state by default.
174 Say N here if you want the default policy to keep all hot-plugged
175 memory blocks in 'offline' state.
177 config MEMORY_HOTREMOVE
178 bool "Allow for memory hot remove"
179 select MEMORY_ISOLATION
180 select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
181 depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
184 # Heavily threaded applications may benefit from splitting the mm-wide
185 # page_table_lock, so that faults on different parts of the user address
186 # space can be handled with less contention: split it at this NR_CPUS.
187 # Default to 4 for wider testing, though 8 might be more appropriate.
188 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
189 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
190 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
192 config SPLIT_PTLOCK_CPUS
194 default "999999" if !MMU
195 default "999999" if ARM && !CPU_CACHE_VIPT
196 default "999999" if PARISC && !PA20
199 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
203 # support for memory balloon
204 config MEMORY_BALLOON
208 # support for memory balloon compaction
209 config BALLOON_COMPACTION
210 bool "Allow for balloon memory compaction/migration"
212 depends on COMPACTION && MEMORY_BALLOON
214 Memory fragmentation introduced by ballooning might reduce
215 significantly the number of 2MB contiguous memory blocks that can be
216 used within a guest, thus imposing performance penalties associated
217 with the reduced number of transparent huge pages that could be used
218 by the guest workload. Allowing the compaction & migration for memory
219 pages enlisted as being part of memory balloon devices avoids the
220 scenario aforementioned and helps improving memory defragmentation.
223 # support for memory compaction
225 bool "Allow for memory compaction"
230 Compaction is the only memory management component to form
231 high order (larger physically contiguous) memory blocks
232 reliably. The page allocator relies on compaction heavily and
233 the lack of the feature can lead to unexpected OOM killer
234 invocations for high order memory requests. You shouldn't
235 disable this option unless there really is a strong reason for
236 it and then we would be really interested to hear about that at
240 # support for page migration
243 bool "Page migration"
245 depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
247 Allows the migration of the physical location of pages of processes
248 while the virtual addresses are not changed. This is useful in
249 two situations. The first is on NUMA systems to put pages nearer
250 to the processors accessing. The second is when allocating huge
251 pages as migration can relocate pages to satisfy a huge page
252 allocation instead of reclaiming.
254 config ARCH_ENABLE_HUGEPAGE_MIGRATION
257 config ARCH_ENABLE_THP_MIGRATION
261 def_bool (MEMORY_ISOLATION && COMPACTION) || CMA
263 config PHYS_ADDR_T_64BIT
267 bool "Enable bounce buffers"
269 depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
271 Enable bounce buffers for devices that cannot access
272 the full range of memory available to the CPU. Enabled
273 by default when ZONE_DMA or HIGHMEM is selected, but you
274 may say n to override this.
279 An architecture should select this if it implements the
280 deprecated interface virt_to_bus(). All new architectures
281 should probably not select this.
290 bool "Enable KSM for page merging"
294 Enable Kernel Samepage Merging: KSM periodically scans those areas
295 of an application's address space that an app has advised may be
296 mergeable. When it finds pages of identical content, it replaces
297 the many instances by a single page with that content, so
298 saving memory until one or another app needs to modify the content.
299 Recommended for use with KVM, or with other duplicative applications.
300 See Documentation/vm/ksm.rst for more information: KSM is inactive
301 until a program has madvised that an area is MADV_MERGEABLE, and
302 root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
304 config DEFAULT_MMAP_MIN_ADDR
305 int "Low address space to protect from user allocation"
309 This is the portion of low virtual memory which should be protected
310 from userspace allocation. Keeping a user from writing to low pages
311 can help reduce the impact of kernel NULL pointer bugs.
313 For most ia64, ppc64 and x86 users with lots of address space
314 a value of 65536 is reasonable and should cause no problems.
315 On arm and other archs it should not be higher than 32768.
316 Programs which use vm86 functionality or have some need to map
317 this low address space will need CAP_SYS_RAWIO or disable this
318 protection by setting the value to 0.
320 This value can be changed after boot using the
321 /proc/sys/vm/mmap_min_addr tunable.
323 config ARCH_SUPPORTS_MEMORY_FAILURE
326 config MEMORY_FAILURE
328 depends on ARCH_SUPPORTS_MEMORY_FAILURE
329 bool "Enable recovery from hardware memory errors"
330 select MEMORY_ISOLATION
333 Enables code to recover from some memory failures on systems
334 with MCA recovery. This allows a system to continue running
335 even when some of its memory has uncorrected errors. This requires
336 special hardware support and typically ECC memory.
338 config HWPOISON_INJECT
339 tristate "HWPoison pages injector"
340 depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
341 select PROC_PAGE_MONITOR
343 config NOMMU_INITIAL_TRIM_EXCESS
344 int "Turn on mmap() excess space trimming before booting"
348 The NOMMU mmap() frequently needs to allocate large contiguous chunks
349 of memory on which to store mappings, but it can only ask the system
350 allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
351 more than it requires. To deal with this, mmap() is able to trim off
352 the excess and return it to the allocator.
354 If trimming is enabled, the excess is trimmed off and returned to the
355 system allocator, which can cause extra fragmentation, particularly
356 if there are a lot of transient processes.
358 If trimming is disabled, the excess is kept, but not used, which for
359 long-term mappings means that the space is wasted.
361 Trimming can be dynamically controlled through a sysctl option
362 (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
363 excess pages there must be before trimming should occur, or zero if
364 no trimming is to occur.
366 This option specifies the initial value of this option. The default
367 of 1 says that all excess pages should be trimmed.
369 See Documentation/nommu-mmap.txt for more information.
371 config TRANSPARENT_HUGEPAGE
372 bool "Transparent Hugepage Support"
373 depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
377 Transparent Hugepages allows the kernel to use huge pages and
378 huge tlb transparently to the applications whenever possible.
379 This feature can improve computing performance to certain
380 applications by speeding up page faults during memory
381 allocation, by reducing the number of tlb misses and by speeding
382 up the pagetable walking.
384 If memory constrained on embedded, you may want to say N.
387 prompt "Transparent Hugepage Support sysfs defaults"
388 depends on TRANSPARENT_HUGEPAGE
389 default TRANSPARENT_HUGEPAGE_ALWAYS
391 Selects the sysfs defaults for Transparent Hugepage Support.
393 config TRANSPARENT_HUGEPAGE_ALWAYS
396 Enabling Transparent Hugepage always, can increase the
397 memory footprint of applications without a guaranteed
398 benefit but it will work automatically for all applications.
400 config TRANSPARENT_HUGEPAGE_MADVISE
403 Enabling Transparent Hugepage madvise, will only provide a
404 performance improvement benefit to the applications using
405 madvise(MADV_HUGEPAGE) but it won't risk to increase the
406 memory footprint of applications without a guaranteed
410 config ARCH_WANTS_THP_SWAP
415 depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP
417 Swap transparent huge pages in one piece, without splitting.
418 XXX: For now, swap cluster backing transparent huge page
419 will be split after swapout.
421 For selection by architectures with reasonable THP sizes.
423 config TRANSPARENT_HUGE_PAGECACHE
425 depends on TRANSPARENT_HUGEPAGE
428 # UP and nommu archs use km based percpu allocator
430 config NEED_PER_CPU_KM
436 bool "Enable cleancache driver to cache clean pages if tmem is present"
438 Cleancache can be thought of as a page-granularity victim cache
439 for clean pages that the kernel's pageframe replacement algorithm
440 (PFRA) would like to keep around, but can't since there isn't enough
441 memory. So when the PFRA "evicts" a page, it first attempts to use
442 cleancache code to put the data contained in that page into
443 "transcendent memory", memory that is not directly accessible or
444 addressable by the kernel and is of unknown and possibly
445 time-varying size. And when a cleancache-enabled
446 filesystem wishes to access a page in a file on disk, it first
447 checks cleancache to see if it already contains it; if it does,
448 the page is copied into the kernel and a disk access is avoided.
449 When a transcendent memory driver is available (such as zcache or
450 Xen transcendent memory), a significant I/O reduction
451 may be achieved. When none is available, all cleancache calls
452 are reduced to a single pointer-compare-against-NULL resulting
453 in a negligible performance hit.
455 If unsure, say Y to enable cleancache
458 bool "Enable frontswap to cache swap pages if tmem is present"
461 Frontswap is so named because it can be thought of as the opposite
462 of a "backing" store for a swap device. The data is stored into
463 "transcendent memory", memory that is not directly accessible or
464 addressable by the kernel and is of unknown and possibly
465 time-varying size. When space in transcendent memory is available,
466 a significant swap I/O reduction may be achieved. When none is
467 available, all frontswap calls are reduced to a single pointer-
468 compare-against-NULL resulting in a negligible performance hit
469 and swap data is stored as normal on the matching swap device.
471 If unsure, say Y to enable frontswap.
474 bool "Contiguous Memory Allocator"
477 select MEMORY_ISOLATION
479 This enables the Contiguous Memory Allocator which allows other
480 subsystems to allocate big physically-contiguous blocks of memory.
481 CMA reserves a region of memory and allows only movable pages to
482 be allocated from it. This way, the kernel can use the memory for
483 pagecache and when a subsystem requests for contiguous area, the
484 allocated pages are migrated away to serve the contiguous request.
489 bool "CMA debug messages (DEVELOPMENT)"
490 depends on DEBUG_KERNEL && CMA
492 Turns on debug messages in CMA. This produces KERN_DEBUG
493 messages for every CMA call as well as various messages while
494 processing calls such as dma_alloc_from_contiguous().
495 This option does not affect warning and error messages.
498 bool "CMA debugfs interface"
499 depends on CMA && DEBUG_FS
501 Turns on the DebugFS interface for CMA.
504 int "Maximum count of the CMA areas"
508 CMA allows to create CMA areas for particular purpose, mainly,
509 used as device private area. This parameter sets the maximum
510 number of CMA area in the system.
512 If unsure, leave the default value "7".
514 config MEM_SOFT_DIRTY
515 bool "Track memory changes"
516 depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
517 select PROC_PAGE_MONITOR
519 This option enables memory changes tracking by introducing a
520 soft-dirty bit on pte-s. This bit it set when someone writes
521 into a page just as regular dirty bit, but unlike the latter
522 it can be cleared by hands.
524 See Documentation/admin-guide/mm/soft-dirty.rst for more details.
527 bool "Compressed cache for swap pages (EXPERIMENTAL)"
528 depends on FRONTSWAP && CRYPTO=y
532 A lightweight compressed cache for swap pages. It takes
533 pages that are in the process of being swapped out and attempts to
534 compress them into a dynamically allocated RAM-based memory pool.
535 This can result in a significant I/O reduction on swap device and,
536 in the case where decompressing from RAM is faster that swap device
537 reads, can also improve workload performance.
539 This is marked experimental because it is a new feature (as of
540 v3.11) that interacts heavily with memory reclaim. While these
541 interactions don't cause any known issues on simple memory setups,
542 they have not be fully explored on the large set of potential
543 configurations and workloads that exist.
546 tristate "Common API for compressed memory storage"
548 Compressed memory storage API. This allows using either zbud or
552 tristate "Low (Up to 2x) density storage for compressed pages"
554 A special purpose allocator for storing compressed pages.
555 It is designed to store up to two compressed pages per physical
556 page. While this design limits storage density, it has simple and
557 deterministic reclaim properties that make it preferable to a higher
558 density approach when reclaim will be used.
561 tristate "Up to 3x density storage for compressed pages"
564 A special purpose allocator for storing compressed pages.
565 It is designed to store up to three compressed pages per physical
566 page. It is a ZBUD derivative so the simplicity and determinism are
570 tristate "Memory allocator for compressed pages"
573 zsmalloc is a slab-based memory allocator designed to store
574 compressed RAM pages. zsmalloc uses virtual memory mapping
575 in order to reduce fragmentation. However, this results in a
576 non-standard allocator interface where a handle, not a pointer, is
577 returned by an alloc(). This handle must be mapped in order to
578 access the allocated space.
580 config PGTABLE_MAPPING
581 bool "Use page table mapping to access object in zsmalloc"
584 By default, zsmalloc uses a copy-based object mapping method to
585 access allocations that span two pages. However, if a particular
586 architecture (ex, ARM) performs VM mapping faster than copying,
587 then you should select this. This causes zsmalloc to use page table
588 mapping rather than copying for object mapping.
590 You can check speed with zsmalloc benchmark:
591 https://github.com/spartacus06/zsmapbench
594 bool "Export zsmalloc statistics"
598 This option enables code in the zsmalloc to collect various
599 statistics about whats happening in zsmalloc and exports that
600 information to userspace via debugfs.
603 config GENERIC_EARLY_IOREMAP
606 config MAX_STACK_SIZE_MB
607 int "Maximum user stack size for 32-bit processes (MB)"
610 depends on STACK_GROWSUP && (!64BIT || COMPAT)
612 This is the maximum stack size in Megabytes in the VM layout of 32-bit
613 user processes when the stack grows upwards (currently only on parisc
614 arch). The stack will be located at the highest memory address minus
615 the given value, unless the RLIMIT_STACK hard limit is changed to a
616 smaller value in which case that is used.
618 A sane initial value is 80 MB.
620 config DEFERRED_STRUCT_PAGE_INIT
621 bool "Defer initialisation of struct pages to kthreads"
623 depends on !NEED_PER_CPU_KM
626 Ordinarily all struct pages are initialised during early boot in a
627 single thread. On very large machines this can take a considerable
628 amount of time. If this option is set, large machines will bring up
629 a subset of memmap at boot and then initialise the rest in parallel
630 by starting one-off "pgdatinitX" kernel thread for each node X. This
631 has a potential performance impact on processes running early in the
632 lifetime of the system until these kthreads finish the
635 config IDLE_PAGE_TRACKING
636 bool "Enable idle page tracking"
637 depends on SYSFS && MMU
638 select PAGE_EXTENSION if !64BIT
640 This feature allows to estimate the amount of user pages that have
641 not been touched during a given period of time. This information can
642 be useful to tune memory cgroup limits and/or for job placement
643 within a compute cluster.
645 See Documentation/admin-guide/mm/idle_page_tracking.rst for
648 config ARCH_HAS_PTE_DEVMAP
652 bool "Device memory (pmem, HMM, etc...) hotplug support"
653 depends on MEMORY_HOTPLUG
654 depends on MEMORY_HOTREMOVE
655 depends on SPARSEMEM_VMEMMAP
656 depends on ARCH_HAS_PTE_DEVMAP
660 Device memory hotplug support allows for establishing pmem,
661 or other device driver discovered memory regions, in the
662 memmap. This allows pfn_to_page() lookups of otherwise
663 "device-physical" addresses which is needed for using a DAX
664 mapping in an O_DIRECT operation, among other things.
666 If FS_DAX is enabled, then say Y.
668 config DEV_PAGEMAP_OPS
672 # Helpers to mirror range of the CPU page tables of a process into device page
679 config DEVICE_PRIVATE
680 bool "Unaddressable device memory (GPU memory, ...)"
681 depends on ZONE_DEVICE
682 select DEV_PAGEMAP_OPS
685 Allows creation of struct pages to represent unaddressable device
686 memory; i.e., memory that is only accessible from the device (or
687 group of devices). You likely also want to select HMM_MIRROR.
692 config ARCH_USES_HIGH_VMA_FLAGS
694 config ARCH_HAS_PKEYS
698 bool "Collect percpu memory statistics"
700 This feature collects and exposes statistics via debugfs. The
701 information includes global and per chunk statistics, which can
702 be used to help understand percpu memory usage.
705 bool "Enable infrastructure for get_user_pages_fast() benchmarking"
707 Provides /sys/kernel/debug/gup_benchmark that helps with testing
708 performance of get_user_pages_fast().
710 See tools/testing/selftests/vm/gup_benchmark.c
712 config GUP_GET_PTE_LOW_HIGH
715 config READ_ONLY_THP_FOR_FS
716 bool "Read-only THP for filesystems (EXPERIMENTAL)"
717 depends on TRANSPARENT_HUGE_PAGECACHE && SHMEM
720 Allow khugepaged to put read-only file-backed pages in THP.
722 This is marked experimental because it is a new feature. Write
723 support of file THPs will be developed in the next few release
726 config ARCH_HAS_PTE_SPECIAL
730 # Some architectures require a special hugepage directory format that is
731 # required to support multiple hugepage sizes. For example a4fe3ce76
732 # "powerpc/mm: Allow more flexible layouts for hugepage pagetables"
733 # introduced it on powerpc. This allows for a more flexible hugepage
736 config ARCH_HAS_HUGEPD
739 config MAPPING_DIRTY_HELPERS