mm/Kconfig

   1 # SPDX-License-Identifier: GPL-2.0-only
   2
   3 menu "Memory Management options"
   4
   5 config SELECT_MEMORY_MODEL
   6         def_bool y
   7         depends on ARCH_SELECT_MEMORY_MODEL
   8
   9 choice
  10         prompt "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
  15         help
  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.
  20
  21 config FLATMEM_MANUAL
  22         bool "Flat Memory"
  23         depends on !(ARCH_DISCONTIGMEM_ENABLE || ARCH_SPARSEMEM_ENABLE) || ARCH_FLATMEM_ENABLE
  24         help
  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.
  29
  30           For systems that have holes in their physical address
  31           spaces and for features like NUMA and memory hotplug,
  32           choose "Sparse Memory"
  33
  34           If unsure, choose this option (Flat Memory) over any other.
  35
  36 config DISCONTIGMEM_MANUAL
  37         bool "Discontiguous Memory"
  38         depends on ARCH_DISCONTIGMEM_ENABLE
  39         help
  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.
  44
  45           Although "Discontiguous Memory" is still used by several
  46           architectures, it is considered deprecated in favor of
  47           "Sparse Memory".
  48
  49           If unsure, choose "Sparse Memory" over this option.
  50
  51 config SPARSEMEM_MANUAL
  52         bool "Sparse Memory"
  53         depends on ARCH_SPARSEMEM_ENABLE
  54         help
  55           This will be the only option for some systems, including
  56           memory hot-plug systems.  This is normal.
  57
  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.
  61
  62           If unsure, choose "Flat Memory" over this option.
  63
  64 endchoice
  65
  66 config DISCONTIGMEM
  67         def_bool y
  68         depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
  69
  70 config SPARSEMEM
  71         def_bool y
  72         depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
  73
  74 config FLATMEM
  75         def_bool y
  76         depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
  77
  78 config FLAT_NODE_MEM_MAP
  79         def_bool y
  80         depends on !SPARSEMEM
  81
  82 #
  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.
  86 #
  87 config NEED_MULTIPLE_NODES
  88         def_bool y
  89         depends on DISCONTIGMEM || NUMA
  90
  91 config HAVE_MEMORY_PRESENT
  92         def_bool y
  93         depends on ARCH_HAVE_MEMORY_PRESENT || SPARSEMEM
  94
  95 #
  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.
 101 #
 102 # This option will also potentially produce smaller runtime code
 103 # with gcc 3.4 and later.
 104 #
 105 config SPARSEMEM_STATIC
 106         bool
 107
 108 #
 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.
 112 #
 113 config SPARSEMEM_EXTREME
 114         def_bool y
 115         depends on SPARSEMEM && !SPARSEMEM_STATIC
 116
 117 config SPARSEMEM_VMEMMAP_ENABLE
 118         bool
 119
 120 config SPARSEMEM_VMEMMAP
 121         bool "Sparse Memory virtual memmap"
 122         depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
 123         default y
 124         help
 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.
 128
 129 config HAVE_MEMBLOCK_NODE_MAP
 130         bool
 131
 132 config HAVE_MEMBLOCK_PHYS_MAP
 133         bool
 134
 135 config HAVE_FAST_GUP
 136         depends on MMU
 137         bool
 138
 139 config ARCH_KEEP_MEMBLOCK
 140         bool
 141
 142 config MEMORY_ISOLATION
 143         bool
 144
 145 #
 146 # Only be set on architectures that have completely implemented memory hotplug
 147 # feature. If you are not sure, don't touch it.
 148 #
 149 config HAVE_BOOTMEM_INFO_NODE
 150         def_bool n
 151
 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
 157
 158 config MEMORY_HOTPLUG_SPARSE
 159         def_bool y
 160         depends on SPARSEMEM && MEMORY_HOTPLUG
 161
 162 config MEMORY_HOTPLUG_DEFAULT_ONLINE
 163         bool "Online the newly added memory blocks by default"
 164         depends on MEMORY_HOTPLUG
 165         help
 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.
 171
 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.
 176
 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
 182         depends on MIGRATION
 183
 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.
 191 #
 192 config SPLIT_PTLOCK_CPUS
 193         int
 194         default "999999" if !MMU
 195         default "999999" if ARM && !CPU_CACHE_VIPT
 196         default "999999" if PARISC && !PA20
 197         default "4"
 198
 199 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
 200         bool
 201
 202 #
 203 # support for memory balloon
 204 config MEMORY_BALLOON
 205         bool
 206
 207 #
 208 # support for memory balloon compaction
 209 config BALLOON_COMPACTION
 210         bool "Allow for balloon memory compaction/migration"
 211         def_bool y
 212         depends on COMPACTION && MEMORY_BALLOON
 213         help
 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.
 221
 222 #
 223 # support for memory compaction
 224 config COMPACTION
 225         bool "Allow for memory compaction"
 226         def_bool y
 227         select MIGRATION
 228         depends on MMU
 229         help
 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
 237           linux-mm@kvack.org.
 238
 239 #
 240 # support for page migration
 241 #
 242 config MIGRATION
 243         bool "Page migration"
 244         def_bool y
 245         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
 246         help
 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.
 253
 254 config ARCH_ENABLE_HUGEPAGE_MIGRATION
 255         bool
 256
 257 config ARCH_ENABLE_THP_MIGRATION
 258         bool
 259
 260 config CONTIG_ALLOC
 261        def_bool (MEMORY_ISOLATION && COMPACTION) || CMA
 262
 263 config PHYS_ADDR_T_64BIT
 264         def_bool 64BIT
 265
 266 config BOUNCE
 267         bool "Enable bounce buffers"
 268         default y
 269         depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 270         help
 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.
 275
 276 config VIRT_TO_BUS
 277         bool
 278         help
 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.
 282
 283
 284 config MMU_NOTIFIER
 285         bool
 286         select SRCU
 287
 288 config KSM
 289         bool "Enable KSM for page merging"
 290         depends on MMU
 291         select XXHASH
 292         help
 293           Enable Kernel Samepage Merging: KSM periodically scans those areas
 294           of an application's address space that an app has advised may be
 295           mergeable.  When it finds pages of identical content, it replaces
 296           the many instances by a single page with that content, so
 297           saving memory until one or another app needs to modify the content.
 298           Recommended for use with KVM, or with other duplicative applications.
 299           See Documentation/vm/ksm.rst for more information: KSM is inactive
 300           until a program has madvised that an area is MADV_MERGEABLE, and
 301           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 302
 303 config DEFAULT_MMAP_MIN_ADDR
 304         int "Low address space to protect from user allocation"
 305         depends on MMU
 306         default 4096
 307         help
 308           This is the portion of low virtual memory which should be protected
 309           from userspace allocation.  Keeping a user from writing to low pages
 310           can help reduce the impact of kernel NULL pointer bugs.
 311
 312           For most ia64, ppc64 and x86 users with lots of address space
 313           a value of 65536 is reasonable and should cause no problems.
 314           On arm and other archs it should not be higher than 32768.
 315           Programs which use vm86 functionality or have some need to map
 316           this low address space will need CAP_SYS_RAWIO or disable this
 317           protection by setting the value to 0.
 318
 319           This value can be changed after boot using the
 320           /proc/sys/vm/mmap_min_addr tunable.
 321
 322 config ARCH_SUPPORTS_MEMORY_FAILURE
 323         bool
 324
 325 config MEMORY_FAILURE
 326         depends on MMU
 327         depends on ARCH_SUPPORTS_MEMORY_FAILURE
 328         bool "Enable recovery from hardware memory errors"
 329         select MEMORY_ISOLATION
 330         select RAS
 331         help
 332           Enables code to recover from some memory failures on systems
 333           with MCA recovery. This allows a system to continue running
 334           even when some of its memory has uncorrected errors. This requires
 335           special hardware support and typically ECC memory.
 336
 337 config HWPOISON_INJECT
 338         tristate "HWPoison pages injector"
 339         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 340         select PROC_PAGE_MONITOR
 341
 342 config NOMMU_INITIAL_TRIM_EXCESS
 343         int "Turn on mmap() excess space trimming before booting"
 344         depends on !MMU
 345         default 1
 346         help
 347           The NOMMU mmap() frequently needs to allocate large contiguous chunks
 348           of memory on which to store mappings, but it can only ask the system
 349           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 350           more than it requires.  To deal with this, mmap() is able to trim off
 351           the excess and return it to the allocator.
 352
 353           If trimming is enabled, the excess is trimmed off and returned to the
 354           system allocator, which can cause extra fragmentation, particularly
 355           if there are a lot of transient processes.
 356
 357           If trimming is disabled, the excess is kept, but not used, which for
 358           long-term mappings means that the space is wasted.
 359
 360           Trimming can be dynamically controlled through a sysctl option
 361           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 362           excess pages there must be before trimming should occur, or zero if
 363           no trimming is to occur.
 364
 365           This option specifies the initial value of this option.  The default
 366           of 1 says that all excess pages should be trimmed.
 367
 368           See Documentation/nommu-mmap.txt for more information.
 369
 370 config TRANSPARENT_HUGEPAGE
 371         bool "Transparent Hugepage Support"
 372         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 373         select COMPACTION
 374         select XARRAY_MULTI
 375         help
 376           Transparent Hugepages allows the kernel to use huge pages and
 377           huge tlb transparently to the applications whenever possible.
 378           This feature can improve computing performance to certain
 379           applications by speeding up page faults during memory
 380           allocation, by reducing the number of tlb misses and by speeding
 381           up the pagetable walking.
 382
 383           If memory constrained on embedded, you may want to say N.
 384
 385 choice
 386         prompt "Transparent Hugepage Support sysfs defaults"
 387         depends on TRANSPARENT_HUGEPAGE
 388         default TRANSPARENT_HUGEPAGE_ALWAYS
 389         help
 390           Selects the sysfs defaults for Transparent Hugepage Support.
 391
 392         config TRANSPARENT_HUGEPAGE_ALWAYS
 393                 bool "always"
 394         help
 395           Enabling Transparent Hugepage always, can increase the
 396           memory footprint of applications without a guaranteed
 397           benefit but it will work automatically for all applications.
 398
 399         config TRANSPARENT_HUGEPAGE_MADVISE
 400                 bool "madvise"
 401         help
 402           Enabling Transparent Hugepage madvise, will only provide a
 403           performance improvement benefit to the applications using
 404           madvise(MADV_HUGEPAGE) but it won't risk to increase the
 405           memory footprint of applications without a guaranteed
 406           benefit.
 407 endchoice
 408
 409 config ARCH_WANTS_THP_SWAP
 410        def_bool n
 411
 412 config THP_SWAP
 413         def_bool y
 414         depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP
 415         help
 416           Swap transparent huge pages in one piece, without splitting.
 417           XXX: For now, swap cluster backing transparent huge page
 418           will be split after swapout.
 419
 420           For selection by architectures with reasonable THP sizes.
 421
 422 config  TRANSPARENT_HUGE_PAGECACHE
 423         def_bool y
 424         depends on TRANSPARENT_HUGEPAGE
 425
 426 #
 427 # UP and nommu archs use km based percpu allocator
 428 #
 429 config NEED_PER_CPU_KM
 430         depends on !SMP
 431         bool
 432         default y
 433
 434 config CLEANCACHE
 435         bool "Enable cleancache driver to cache clean pages if tmem is present"
 436         help
 437           Cleancache can be thought of as a page-granularity victim cache
 438           for clean pages that the kernel's pageframe replacement algorithm
 439           (PFRA) would like to keep around, but can't since there isn't enough
 440           memory.  So when the PFRA "evicts" a page, it first attempts to use
 441           cleancache code to put the data contained in that page into
 442           "transcendent memory", memory that is not directly accessible or
 443           addressable by the kernel and is of unknown and possibly
 444           time-varying size.  And when a cleancache-enabled
 445           filesystem wishes to access a page in a file on disk, it first
 446           checks cleancache to see if it already contains it; if it does,
 447           the page is copied into the kernel and a disk access is avoided.
 448           When a transcendent memory driver is available (such as zcache or
 449           Xen transcendent memory), a significant I/O reduction
 450           may be achieved.  When none is available, all cleancache calls
 451           are reduced to a single pointer-compare-against-NULL resulting
 452           in a negligible performance hit.
 453
 454           If unsure, say Y to enable cleancache
 455
 456 config FRONTSWAP
 457         bool "Enable frontswap to cache swap pages if tmem is present"
 458         depends on SWAP
 459         help
 460           Frontswap is so named because it can be thought of as the opposite
 461           of a "backing" store for a swap device.  The data is stored into
 462           "transcendent memory", memory that is not directly accessible or
 463           addressable by the kernel and is of unknown and possibly
 464           time-varying size.  When space in transcendent memory is available,
 465           a significant swap I/O reduction may be achieved.  When none is
 466           available, all frontswap calls are reduced to a single pointer-
 467           compare-against-NULL resulting in a negligible performance hit
 468           and swap data is stored as normal on the matching swap device.
 469
 470           If unsure, say Y to enable frontswap.
 471
 472 config CMA
 473         bool "Contiguous Memory Allocator"
 474         depends on MMU
 475         select MIGRATION
 476         select MEMORY_ISOLATION
 477         help
 478           This enables the Contiguous Memory Allocator which allows other
 479           subsystems to allocate big physically-contiguous blocks of memory.
 480           CMA reserves a region of memory and allows only movable pages to
 481           be allocated from it. This way, the kernel can use the memory for
 482           pagecache and when a subsystem requests for contiguous area, the
 483           allocated pages are migrated away to serve the contiguous request.
 484
 485           If unsure, say "n".
 486
 487 config CMA_DEBUG
 488         bool "CMA debug messages (DEVELOPMENT)"
 489         depends on DEBUG_KERNEL && CMA
 490         help
 491           Turns on debug messages in CMA.  This produces KERN_DEBUG
 492           messages for every CMA call as well as various messages while
 493           processing calls such as dma_alloc_from_contiguous().
 494           This option does not affect warning and error messages.
 495
 496 config CMA_DEBUGFS
 497         bool "CMA debugfs interface"
 498         depends on CMA && DEBUG_FS
 499         help
 500           Turns on the DebugFS interface for CMA.
 501
 502 config CMA_AREAS
 503         int "Maximum count of the CMA areas"
 504         depends on CMA
 505         default 7
 506         help
 507           CMA allows to create CMA areas for particular purpose, mainly,
 508           used as device private area. This parameter sets the maximum
 509           number of CMA area in the system.
 510
 511           If unsure, leave the default value "7".
 512
 513 config MEM_SOFT_DIRTY
 514         bool "Track memory changes"
 515         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
 516         select PROC_PAGE_MONITOR
 517         help
 518           This option enables memory changes tracking by introducing a
 519           soft-dirty bit on pte-s. This bit it set when someone writes
 520           into a page just as regular dirty bit, but unlike the latter
 521           it can be cleared by hands.
 522
 523           See Documentation/admin-guide/mm/soft-dirty.rst for more details.
 524
 525 config ZSWAP
 526         bool "Compressed cache for swap pages (EXPERIMENTAL)"
 527         depends on FRONTSWAP && CRYPTO=y
 528         select CRYPTO_LZO
 529         select ZPOOL
 530         help
 531           A lightweight compressed cache for swap pages.  It takes
 532           pages that are in the process of being swapped out and attempts to
 533           compress them into a dynamically allocated RAM-based memory pool.
 534           This can result in a significant I/O reduction on swap device and,
 535           in the case where decompressing from RAM is faster that swap device
 536           reads, can also improve workload performance.
 537
 538           This is marked experimental because it is a new feature (as of
 539           v3.11) that interacts heavily with memory reclaim.  While these
 540           interactions don't cause any known issues on simple memory setups,
 541           they have not be fully explored on the large set of potential
 542           configurations and workloads that exist.
 543
 544 config ZPOOL
 545         tristate "Common API for compressed memory storage"
 546         help
 547           Compressed memory storage API.  This allows using either zbud or
 548           zsmalloc.
 549
 550 config ZBUD
 551         tristate "Low (Up to 2x) density storage for compressed pages"
 552         help
 553           A special purpose allocator for storing compressed pages.
 554           It is designed to store up to two compressed pages per physical
 555           page.  While this design limits storage density, it has simple and
 556           deterministic reclaim properties that make it preferable to a higher
 557           density approach when reclaim will be used.
 558
 559 config Z3FOLD
 560         tristate "Up to 3x density storage for compressed pages"
 561         depends on ZPOOL
 562         help
 563           A special purpose allocator for storing compressed pages.
 564           It is designed to store up to three compressed pages per physical
 565           page. It is a ZBUD derivative so the simplicity and determinism are
 566           still there.
 567
 568 config ZSMALLOC
 569         tristate "Memory allocator for compressed pages"
 570         depends on MMU
 571         help
 572           zsmalloc is a slab-based memory allocator designed to store
 573           compressed RAM pages.  zsmalloc uses virtual memory mapping
 574           in order to reduce fragmentation.  However, this results in a
 575           non-standard allocator interface where a handle, not a pointer, is
 576           returned by an alloc().  This handle must be mapped in order to
 577           access the allocated space.
 578
 579 config ZSMALLOC_STAT
 580         bool "Export zsmalloc statistics"
 581         depends on ZSMALLOC
 582         select DEBUG_FS
 583         help
 584           This option enables code in the zsmalloc to collect various
 585           statistics about whats happening in zsmalloc and exports that
 586           information to userspace via debugfs.
 587           If unsure, say N.
 588
 589 config GENERIC_EARLY_IOREMAP
 590         bool
 591
 592 config MAX_STACK_SIZE_MB
 593         int "Maximum user stack size for 32-bit processes (MB)"
 594         default 80
 595         range 8 2048
 596         depends on STACK_GROWSUP && (!64BIT || COMPAT)
 597         help
 598           This is the maximum stack size in Megabytes in the VM layout of 32-bit
 599           user processes when the stack grows upwards (currently only on parisc
 600           arch). The stack will be located at the highest memory address minus
 601           the given value, unless the RLIMIT_STACK hard limit is changed to a
 602           smaller value in which case that is used.
 603
 604           A sane initial value is 80 MB.
 605
 606 config DEFERRED_STRUCT_PAGE_INIT
 607         bool "Defer initialisation of struct pages to kthreads"
 608         depends on SPARSEMEM
 609         depends on !NEED_PER_CPU_KM
 610         depends on 64BIT
 611         help
 612           Ordinarily all struct pages are initialised during early boot in a
 613           single thread. On very large machines this can take a considerable
 614           amount of time. If this option is set, large machines will bring up
 615           a subset of memmap at boot and then initialise the rest in parallel
 616           by starting one-off "pgdatinitX" kernel thread for each node X. This
 617           has a potential performance impact on processes running early in the
 618           lifetime of the system until these kthreads finish the
 619           initialisation.
 620
 621 config IDLE_PAGE_TRACKING
 622         bool "Enable idle page tracking"
 623         depends on SYSFS && MMU
 624         select PAGE_EXTENSION if !64BIT
 625         help
 626           This feature allows to estimate the amount of user pages that have
 627           not been touched during a given period of time. This information can
 628           be useful to tune memory cgroup limits and/or for job placement
 629           within a compute cluster.
 630
 631           See Documentation/admin-guide/mm/idle_page_tracking.rst for
 632           more details.
 633
 634 config ARCH_HAS_PTE_DEVMAP
 635         bool
 636
 637 config ZONE_DEVICE
 638         bool "Device memory (pmem, HMM, etc...) hotplug support"
 639         depends on MEMORY_HOTPLUG
 640         depends on MEMORY_HOTREMOVE
 641         depends on SPARSEMEM_VMEMMAP
 642         depends on ARCH_HAS_PTE_DEVMAP
 643         select XARRAY_MULTI
 644
 645         help
 646           Device memory hotplug support allows for establishing pmem,
 647           or other device driver discovered memory regions, in the
 648           memmap. This allows pfn_to_page() lookups of otherwise
 649           "device-physical" addresses which is needed for using a DAX
 650           mapping in an O_DIRECT operation, among other things.
 651
 652           If FS_DAX is enabled, then say Y.
 653
 654 config DEV_PAGEMAP_OPS
 655         bool
 656
 657 #
 658 # Helpers to mirror range of the CPU page tables of a process into device page
 659 # tables.
 660 #
 661 config HMM_MIRROR
 662         bool
 663         depends on MMU
 664         depends on MMU_NOTIFIER
 665
 666 config DEVICE_PRIVATE
 667         bool "Unaddressable device memory (GPU memory, ...)"
 668         depends on ZONE_DEVICE
 669         select DEV_PAGEMAP_OPS
 670
 671         help
 672           Allows creation of struct pages to represent unaddressable device
 673           memory; i.e., memory that is only accessible from the device (or
 674           group of devices). You likely also want to select HMM_MIRROR.
 675
 676 config FRAME_VECTOR
 677         bool
 678
 679 config ARCH_USES_HIGH_VMA_FLAGS
 680         bool
 681 config ARCH_HAS_PKEYS
 682         bool
 683
 684 config PERCPU_STATS
 685         bool "Collect percpu memory statistics"
 686         help
 687           This feature collects and exposes statistics via debugfs. The
 688           information includes global and per chunk statistics, which can
 689           be used to help understand percpu memory usage.
 690
 691 config GUP_BENCHMARK
 692         bool "Enable infrastructure for get_user_pages_fast() benchmarking"
 693         help
 694           Provides /sys/kernel/debug/gup_benchmark that helps with testing
 695           performance of get_user_pages_fast().
 696
 697           See tools/testing/selftests/vm/gup_benchmark.c
 698
 699 config GUP_GET_PTE_LOW_HIGH
 700         bool
 701
 702 config READ_ONLY_THP_FOR_FS
 703         bool "Read-only THP for filesystems (EXPERIMENTAL)"
 704         depends on TRANSPARENT_HUGE_PAGECACHE && SHMEM
 705
 706         help
 707           Allow khugepaged to put read-only file-backed pages in THP.
 708
 709           This is marked experimental because it is a new feature. Write
 710           support of file THPs will be developed in the next few release
 711           cycles.
 712
 713 config ARCH_HAS_PTE_SPECIAL
 714         bool
 715
 716 #
 717 # Some architectures require a special hugepage directory format that is
 718 # required to support multiple hugepage sizes. For example a4fe3ce76
 719 # "powerpc/mm: Allow more flexible layouts for hugepage pagetables"
 720 # introduced it on powerpc.  This allows for a more flexible hugepage
 721 # pagetable layouts.
 722 #
 723 config ARCH_HAS_HUGEPD
 724         bool
 725
 726 endmenu