mm/Kconfig

   1
   2 menu "Memory Management options"
   3
   4 config SELECT_MEMORY_MODEL
   5         def_bool y
   6         depends on ARCH_SELECT_MEMORY_MODEL
   7
   8 choice
   9         prompt "Memory model"
  10         depends on SELECT_MEMORY_MODEL
  11         default DISCONTIGMEM_MANUAL if ARCH_DISCONTIGMEM_DEFAULT
  12         default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
  13         default FLATMEM_MANUAL
  14
  15 config FLATMEM_MANUAL
  16         bool "Flat Memory"
  17         depends on !(ARCH_DISCONTIGMEM_ENABLE || ARCH_SPARSEMEM_ENABLE) || ARCH_FLATMEM_ENABLE
  18         help
  19           This option allows you to change some of the ways that
  20           Linux manages its memory internally.  Most users will
  21           only have one option here: FLATMEM.  This is normal
  22           and a correct option.
  23
  24           Some users of more advanced features like NUMA and
  25           memory hotplug may have different options here.
  26           DISCONTIGMEM is a more mature, better tested system,
  27           but is incompatible with memory hotplug and may suffer
  28           decreased performance over SPARSEMEM.  If unsure between
  29           "Sparse Memory" and "Discontiguous Memory", choose
  30           "Discontiguous Memory".
  31
  32           If unsure, choose this option (Flat Memory) over any other.
  33
  34 config DISCONTIGMEM_MANUAL
  35         bool "Discontiguous Memory"
  36         depends on ARCH_DISCONTIGMEM_ENABLE
  37         help
  38           This option provides enhanced support for discontiguous
  39           memory systems, over FLATMEM.  These systems have holes
  40           in their physical address spaces, and this option provides
  41           more efficient handling of these holes.  However, the vast
  42           majority of hardware has quite flat address spaces, and
  43           can have degraded performance from the extra overhead that
  44           this option imposes.
  45
  46           Many NUMA configurations will have this as the only option.
  47
  48           If unsure, choose "Flat Memory" over this option.
  49
  50 config SPARSEMEM_MANUAL
  51         bool "Sparse Memory"
  52         depends on ARCH_SPARSEMEM_ENABLE
  53         help
  54           This will be the only option for some systems, including
  55           memory hotplug systems.  This is normal.
  56
  57           For many other systems, this will be an alternative to
  58           "Discontiguous Memory".  This option provides some potential
  59           performance benefits, along with decreased code complexity,
  60           but it is newer, and more experimental.
  61
  62           If unsure, choose "Discontiguous Memory" or "Flat Memory"
  63           over this option.
  64
  65 endchoice
  66
  67 config DISCONTIGMEM
  68         def_bool y
  69         depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
  70
  71 config SPARSEMEM
  72         def_bool y
  73         depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
  74
  75 config FLATMEM
  76         def_bool y
  77         depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
  78
  79 config FLAT_NODE_MEM_MAP
  80         def_bool y
  81         depends on !SPARSEMEM
  82
  83 #
  84 # Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's
  85 # to represent different areas of memory.  This variable allows
  86 # those dependencies to exist individually.
  87 #
  88 config NEED_MULTIPLE_NODES
  89         def_bool y
  90         depends on DISCONTIGMEM || NUMA
  91
  92 config HAVE_MEMORY_PRESENT
  93         def_bool y
  94         depends on ARCH_HAVE_MEMORY_PRESENT || SPARSEMEM
  95
  96 #
  97 # SPARSEMEM_EXTREME (which is the default) does some bootmem
  98 # allocations when memory_present() is called.  If this cannot
  99 # be done on your architecture, select this option.  However,
 100 # statically allocating the mem_section[] array can potentially
 101 # consume vast quantities of .bss, so be careful.
 102 #
 103 # This option will also potentially produce smaller runtime code
 104 # with gcc 3.4 and later.
 105 #
 106 config SPARSEMEM_STATIC
 107         bool
 108
 109 #
 110 # Architecture platforms which require a two level mem_section in SPARSEMEM
 111 # must select this option. This is usually for architecture platforms with
 112 # an extremely sparse physical address space.
 113 #
 114 config SPARSEMEM_EXTREME
 115         def_bool y
 116         depends on SPARSEMEM && !SPARSEMEM_STATIC
 117
 118 config SPARSEMEM_VMEMMAP_ENABLE
 119         bool
 120
 121 config SPARSEMEM_VMEMMAP
 122         bool "Sparse Memory virtual memmap"
 123         depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
 124         default y
 125         help
 126          SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
 127          pfn_to_page and page_to_pfn operations.  This is the most
 128          efficient option when sufficient kernel resources are available.
 129
 130 config HAVE_MEMBLOCK_NODE_MAP
 131         bool
 132
 133 config HAVE_MEMBLOCK_PHYS_MAP
 134         bool
 135
 136 config HAVE_GENERIC_GUP
 137         bool
 138
 139 config ARCH_DISCARD_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         default n
 165         depends on MEMORY_HOTPLUG
 166         help
 167           This option sets the default policy setting for memory hotplug
 168           onlining policy (/sys/devices/system/memory/auto_online_blocks) which
 169           determines what happens to newly added memory regions. Policy setting
 170           can always be changed at runtime.
 171           See Documentation/memory-hotplug.txt for more information.
 172
 173           Say Y here if you want all hot-plugged memory blocks to appear in
 174           'online' state by default.
 175           Say N here if you want the default policy to keep all hot-plugged
 176           memory blocks in 'offline' state.
 177
 178 config MEMORY_HOTREMOVE
 179         bool "Allow for memory hot remove"
 180         select MEMORY_ISOLATION
 181         select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
 182         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 183         depends on MIGRATION
 184
 185 # Heavily threaded applications may benefit from splitting the mm-wide
 186 # page_table_lock, so that faults on different parts of the user address
 187 # space can be handled with less contention: split it at this NR_CPUS.
 188 # Default to 4 for wider testing, though 8 might be more appropriate.
 189 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 190 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 191 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 192 #
 193 config SPLIT_PTLOCK_CPUS
 194         int
 195         default "999999" if !MMU
 196         default "999999" if ARM && !CPU_CACHE_VIPT
 197         default "999999" if PARISC && !PA20
 198         default "4"
 199
 200 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
 201         bool
 202
 203 #
 204 # support for memory balloon
 205 config MEMORY_BALLOON
 206         bool
 207
 208 #
 209 # support for memory balloon compaction
 210 config BALLOON_COMPACTION
 211         bool "Allow for balloon memory compaction/migration"
 212         def_bool y
 213         depends on COMPACTION && MEMORY_BALLOON
 214         help
 215           Memory fragmentation introduced by ballooning might reduce
 216           significantly the number of 2MB contiguous memory blocks that can be
 217           used within a guest, thus imposing performance penalties associated
 218           with the reduced number of transparent huge pages that could be used
 219           by the guest workload. Allowing the compaction & migration for memory
 220           pages enlisted as being part of memory balloon devices avoids the
 221           scenario aforementioned and helps improving memory defragmentation.
 222
 223 #
 224 # support for memory compaction
 225 config COMPACTION
 226         bool "Allow for memory compaction"
 227         def_bool y
 228         select MIGRATION
 229         depends on MMU
 230         help
 231           Compaction is the only memory management component to form
 232           high order (larger physically contiguous) memory blocks
 233           reliably. The page allocator relies on compaction heavily and
 234           the lack of the feature can lead to unexpected OOM killer
 235           invocations for high order memory requests. You shouldn't
 236           disable this option unless there really is a strong reason for
 237           it and then we would be really interested to hear about that at
 238           linux-mm@kvack.org.
 239
 240 #
 241 # support for page migration
 242 #
 243 config MIGRATION
 244         bool "Page migration"
 245         def_bool y
 246         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
 247         help
 248           Allows the migration of the physical location of pages of processes
 249           while the virtual addresses are not changed. This is useful in
 250           two situations. The first is on NUMA systems to put pages nearer
 251           to the processors accessing. The second is when allocating huge
 252           pages as migration can relocate pages to satisfy a huge page
 253           allocation instead of reclaiming.
 254
 255 config ARCH_ENABLE_HUGEPAGE_MIGRATION
 256         bool
 257
 258 config ARCH_ENABLE_THP_MIGRATION
 259         bool
 260
 261 config PHYS_ADDR_T_64BIT
 262         def_bool 64BIT
 263
 264 config BOUNCE
 265         bool "Enable bounce buffers"
 266         default y
 267         depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 268         help
 269           Enable bounce buffers for devices that cannot access
 270           the full range of memory available to the CPU. Enabled
 271           by default when ZONE_DMA or HIGHMEM is selected, but you
 272           may say n to override this.
 273
 274 config NR_QUICK
 275         int
 276         depends on QUICKLIST
 277         default "1"
 278
 279 config VIRT_TO_BUS
 280         bool
 281         help
 282           An architecture should select this if it implements the
 283           deprecated interface virt_to_bus().  All new architectures
 284           should probably not select this.
 285
 286
 287 config MMU_NOTIFIER
 288         bool
 289         select SRCU
 290
 291 config KSM
 292         bool "Enable KSM for page merging"
 293         depends on MMU
 294         select XXHASH
 295         help
 296           Enable Kernel Samepage Merging: KSM periodically scans those areas
 297           of an application's address space that an app has advised may be
 298           mergeable.  When it finds pages of identical content, it replaces
 299           the many instances by a single page with that content, so
 300           saving memory until one or another app needs to modify the content.
 301           Recommended for use with KVM, or with other duplicative applications.
 302           See Documentation/vm/ksm.rst for more information: KSM is inactive
 303           until a program has madvised that an area is MADV_MERGEABLE, and
 304           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 305
 306 config DEFAULT_MMAP_MIN_ADDR
 307         int "Low address space to protect from user allocation"
 308         depends on MMU
 309         default 4096
 310         help
 311           This is the portion of low virtual memory which should be protected
 312           from userspace allocation.  Keeping a user from writing to low pages
 313           can help reduce the impact of kernel NULL pointer bugs.
 314
 315           For most ia64, ppc64 and x86 users with lots of address space
 316           a value of 65536 is reasonable and should cause no problems.
 317           On arm and other archs it should not be higher than 32768.
 318           Programs which use vm86 functionality or have some need to map
 319           this low address space will need CAP_SYS_RAWIO or disable this
 320           protection by setting the value to 0.
 321
 322           This value can be changed after boot using the
 323           /proc/sys/vm/mmap_min_addr tunable.
 324
 325 config ARCH_SUPPORTS_MEMORY_FAILURE
 326         bool
 327
 328 config MEMORY_FAILURE
 329         depends on MMU
 330         depends on ARCH_SUPPORTS_MEMORY_FAILURE
 331         bool "Enable recovery from hardware memory errors"
 332         select MEMORY_ISOLATION
 333         select RAS
 334         help
 335           Enables code to recover from some memory failures on systems
 336           with MCA recovery. This allows a system to continue running
 337           even when some of its memory has uncorrected errors. This requires
 338           special hardware support and typically ECC memory.
 339
 340 config HWPOISON_INJECT
 341         tristate "HWPoison pages injector"
 342         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 343         select PROC_PAGE_MONITOR
 344
 345 config NOMMU_INITIAL_TRIM_EXCESS
 346         int "Turn on mmap() excess space trimming before booting"
 347         depends on !MMU
 348         default 1
 349         help
 350           The NOMMU mmap() frequently needs to allocate large contiguous chunks
 351           of memory on which to store mappings, but it can only ask the system
 352           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 353           more than it requires.  To deal with this, mmap() is able to trim off
 354           the excess and return it to the allocator.
 355
 356           If trimming is enabled, the excess is trimmed off and returned to the
 357           system allocator, which can cause extra fragmentation, particularly
 358           if there are a lot of transient processes.
 359
 360           If trimming is disabled, the excess is kept, but not used, which for
 361           long-term mappings means that the space is wasted.
 362
 363           Trimming can be dynamically controlled through a sysctl option
 364           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 365           excess pages there must be before trimming should occur, or zero if
 366           no trimming is to occur.
 367
 368           This option specifies the initial value of this option.  The default
 369           of 1 says that all excess pages should be trimmed.
 370
 371           See Documentation/nommu-mmap.txt for more information.
 372
 373 config TRANSPARENT_HUGEPAGE
 374         bool "Transparent Hugepage Support"
 375         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 376         select COMPACTION
 377         select XARRAY_MULTI
 378         help
 379           Transparent Hugepages allows the kernel to use huge pages and
 380           huge tlb transparently to the applications whenever possible.
 381           This feature can improve computing performance to certain
 382           applications by speeding up page faults during memory
 383           allocation, by reducing the number of tlb misses and by speeding
 384           up the pagetable walking.
 385
 386           If memory constrained on embedded, you may want to say N.
 387
 388 choice
 389         prompt "Transparent Hugepage Support sysfs defaults"
 390         depends on TRANSPARENT_HUGEPAGE
 391         default TRANSPARENT_HUGEPAGE_ALWAYS
 392         help
 393           Selects the sysfs defaults for Transparent Hugepage Support.
 394
 395         config TRANSPARENT_HUGEPAGE_ALWAYS
 396                 bool "always"
 397         help
 398           Enabling Transparent Hugepage always, can increase the
 399           memory footprint of applications without a guaranteed
 400           benefit but it will work automatically for all applications.
 401
 402         config TRANSPARENT_HUGEPAGE_MADVISE
 403                 bool "madvise"
 404         help
 405           Enabling Transparent Hugepage madvise, will only provide a
 406           performance improvement benefit to the applications using
 407           madvise(MADV_HUGEPAGE) but it won't risk to increase the
 408           memory footprint of applications without a guaranteed
 409           benefit.
 410 endchoice
 411
 412 config ARCH_WANTS_THP_SWAP
 413        def_bool n
 414
 415 config THP_SWAP
 416         def_bool y
 417         depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP
 418         help
 419           Swap transparent huge pages in one piece, without splitting.
 420           XXX: For now, swap cluster backing transparent huge page
 421           will be split after swapout.
 422
 423           For selection by architectures with reasonable THP sizes.
 424
 425 config  TRANSPARENT_HUGE_PAGECACHE
 426         def_bool y
 427         depends on TRANSPARENT_HUGEPAGE
 428
 429 #
 430 # UP and nommu archs use km based percpu allocator
 431 #
 432 config NEED_PER_CPU_KM
 433         depends on !SMP
 434         bool
 435         default y
 436
 437 config CLEANCACHE
 438         bool "Enable cleancache driver to cache clean pages if tmem is present"
 439         default n
 440         help
 441           Cleancache can be thought of as a page-granularity victim cache
 442           for clean pages that the kernel's pageframe replacement algorithm
 443           (PFRA) would like to keep around, but can't since there isn't enough
 444           memory.  So when the PFRA "evicts" a page, it first attempts to use
 445           cleancache code to put the data contained in that page into
 446           "transcendent memory", memory that is not directly accessible or
 447           addressable by the kernel and is of unknown and possibly
 448           time-varying size.  And when a cleancache-enabled
 449           filesystem wishes to access a page in a file on disk, it first
 450           checks cleancache to see if it already contains it; if it does,
 451           the page is copied into the kernel and a disk access is avoided.
 452           When a transcendent memory driver is available (such as zcache or
 453           Xen transcendent memory), a significant I/O reduction
 454           may be achieved.  When none is available, all cleancache calls
 455           are reduced to a single pointer-compare-against-NULL resulting
 456           in a negligible performance hit.
 457
 458           If unsure, say Y to enable cleancache
 459
 460 config FRONTSWAP
 461         bool "Enable frontswap to cache swap pages if tmem is present"
 462         depends on SWAP
 463         default n
 464         help
 465           Frontswap is so named because it can be thought of as the opposite
 466           of a "backing" store for a swap device.  The data is stored into
 467           "transcendent memory", memory that is not directly accessible or
 468           addressable by the kernel and is of unknown and possibly
 469           time-varying size.  When space in transcendent memory is available,
 470           a significant swap I/O reduction may be achieved.  When none is
 471           available, all frontswap calls are reduced to a single pointer-
 472           compare-against-NULL resulting in a negligible performance hit
 473           and swap data is stored as normal on the matching swap device.
 474
 475           If unsure, say Y to enable frontswap.
 476
 477 config CMA
 478         bool "Contiguous Memory Allocator"
 479         depends on MMU
 480         select MIGRATION
 481         select MEMORY_ISOLATION
 482         help
 483           This enables the Contiguous Memory Allocator which allows other
 484           subsystems to allocate big physically-contiguous blocks of memory.
 485           CMA reserves a region of memory and allows only movable pages to
 486           be allocated from it. This way, the kernel can use the memory for
 487           pagecache and when a subsystem requests for contiguous area, the
 488           allocated pages are migrated away to serve the contiguous request.
 489
 490           If unsure, say "n".
 491
 492 config CMA_DEBUG
 493         bool "CMA debug messages (DEVELOPMENT)"
 494         depends on DEBUG_KERNEL && CMA
 495         help
 496           Turns on debug messages in CMA.  This produces KERN_DEBUG
 497           messages for every CMA call as well as various messages while
 498           processing calls such as dma_alloc_from_contiguous().
 499           This option does not affect warning and error messages.
 500
 501 config CMA_DEBUGFS
 502         bool "CMA debugfs interface"
 503         depends on CMA && DEBUG_FS
 504         help
 505           Turns on the DebugFS interface for CMA.
 506
 507 config CMA_AREAS
 508         int "Maximum count of the CMA areas"
 509         depends on CMA
 510         default 7
 511         help
 512           CMA allows to create CMA areas for particular purpose, mainly,
 513           used as device private area. This parameter sets the maximum
 514           number of CMA area in the system.
 515
 516           If unsure, leave the default value "7".
 517
 518 config MEM_SOFT_DIRTY
 519         bool "Track memory changes"
 520         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
 521         select PROC_PAGE_MONITOR
 522         help
 523           This option enables memory changes tracking by introducing a
 524           soft-dirty bit on pte-s. This bit it set when someone writes
 525           into a page just as regular dirty bit, but unlike the latter
 526           it can be cleared by hands.
 527
 528           See Documentation/admin-guide/mm/soft-dirty.rst for more details.
 529
 530 config ZSWAP
 531         bool "Compressed cache for swap pages (EXPERIMENTAL)"
 532         depends on FRONTSWAP && CRYPTO=y
 533         select CRYPTO_LZO
 534         select ZPOOL
 535         default n
 536         help
 537           A lightweight compressed cache for swap pages.  It takes
 538           pages that are in the process of being swapped out and attempts to
 539           compress them into a dynamically allocated RAM-based memory pool.
 540           This can result in a significant I/O reduction on swap device and,
 541           in the case where decompressing from RAM is faster that swap device
 542           reads, can also improve workload performance.
 543
 544           This is marked experimental because it is a new feature (as of
 545           v3.11) that interacts heavily with memory reclaim.  While these
 546           interactions don't cause any known issues on simple memory setups,
 547           they have not be fully explored on the large set of potential
 548           configurations and workloads that exist.
 549
 550 config ZPOOL
 551         tristate "Common API for compressed memory storage"
 552         default n
 553         help
 554           Compressed memory storage API.  This allows using either zbud or
 555           zsmalloc.
 556
 557 config ZBUD
 558         tristate "Low (Up to 2x) density storage for compressed pages"
 559         default n
 560         help
 561           A special purpose allocator for storing compressed pages.
 562           It is designed to store up to two compressed pages per physical
 563           page.  While this design limits storage density, it has simple and
 564           deterministic reclaim properties that make it preferable to a higher
 565           density approach when reclaim will be used.
 566
 567 config Z3FOLD
 568         tristate "Up to 3x density storage for compressed pages"
 569         depends on ZPOOL
 570         default n
 571         help
 572           A special purpose allocator for storing compressed pages.
 573           It is designed to store up to three compressed pages per physical
 574           page. It is a ZBUD derivative so the simplicity and determinism are
 575           still there.
 576
 577 config ZSMALLOC
 578         tristate "Memory allocator for compressed pages"
 579         depends on MMU
 580         default n
 581         help
 582           zsmalloc is a slab-based memory allocator designed to store
 583           compressed RAM pages.  zsmalloc uses virtual memory mapping
 584           in order to reduce fragmentation.  However, this results in a
 585           non-standard allocator interface where a handle, not a pointer, is
 586           returned by an alloc().  This handle must be mapped in order to
 587           access the allocated space.
 588
 589 config PGTABLE_MAPPING
 590         bool "Use page table mapping to access object in zsmalloc"
 591         depends on ZSMALLOC
 592         help
 593           By default, zsmalloc uses a copy-based object mapping method to
 594           access allocations that span two pages. However, if a particular
 595           architecture (ex, ARM) performs VM mapping faster than copying,
 596           then you should select this. This causes zsmalloc to use page table
 597           mapping rather than copying for object mapping.
 598
 599           You can check speed with zsmalloc benchmark:
 600           https://github.com/spartacus06/zsmapbench
 601
 602 config ZSMALLOC_STAT
 603         bool "Export zsmalloc statistics"
 604         depends on ZSMALLOC
 605         select DEBUG_FS
 606         help
 607           This option enables code in the zsmalloc to collect various
 608           statistics about whats happening in zsmalloc and exports that
 609           information to userspace via debugfs.
 610           If unsure, say N.
 611
 612 config GENERIC_EARLY_IOREMAP
 613         bool
 614
 615 config MAX_STACK_SIZE_MB
 616         int "Maximum user stack size for 32-bit processes (MB)"
 617         default 80
 618         range 8 2048
 619         depends on STACK_GROWSUP && (!64BIT || COMPAT)
 620         help
 621           This is the maximum stack size in Megabytes in the VM layout of 32-bit
 622           user processes when the stack grows upwards (currently only on parisc
 623           arch). The stack will be located at the highest memory address minus
 624           the given value, unless the RLIMIT_STACK hard limit is changed to a
 625           smaller value in which case that is used.
 626
 627           A sane initial value is 80 MB.
 628
 629 config DEFERRED_STRUCT_PAGE_INIT
 630         bool "Defer initialisation of struct pages to kthreads"
 631         default n
 632         depends on SPARSEMEM
 633         depends on !NEED_PER_CPU_KM
 634         depends on 64BIT
 635         help
 636           Ordinarily all struct pages are initialised during early boot in a
 637           single thread. On very large machines this can take a considerable
 638           amount of time. If this option is set, large machines will bring up
 639           a subset of memmap at boot and then initialise the rest in parallel
 640           by starting one-off "pgdatinitX" kernel thread for each node X. This
 641           has a potential performance impact on processes running early in the
 642           lifetime of the system until these kthreads finish the
 643           initialisation.
 644
 645 config IDLE_PAGE_TRACKING
 646         bool "Enable idle page tracking"
 647         depends on SYSFS && MMU
 648         select PAGE_EXTENSION if !64BIT
 649         help
 650           This feature allows to estimate the amount of user pages that have
 651           not been touched during a given period of time. This information can
 652           be useful to tune memory cgroup limits and/or for job placement
 653           within a compute cluster.
 654
 655           See Documentation/admin-guide/mm/idle_page_tracking.rst for
 656           more details.
 657
 658 # arch_add_memory() comprehends device memory
 659 config ARCH_HAS_ZONE_DEVICE
 660         bool
 661
 662 config ZONE_DEVICE
 663         bool "Device memory (pmem, HMM, etc...) hotplug support"
 664         depends on MEMORY_HOTPLUG
 665         depends on MEMORY_HOTREMOVE
 666         depends on SPARSEMEM_VMEMMAP
 667         depends on ARCH_HAS_ZONE_DEVICE
 668         select XARRAY_MULTI
 669
 670         help
 671           Device memory hotplug support allows for establishing pmem,
 672           or other device driver discovered memory regions, in the
 673           memmap. This allows pfn_to_page() lookups of otherwise
 674           "device-physical" addresses which is needed for using a DAX
 675           mapping in an O_DIRECT operation, among other things.
 676
 677           If FS_DAX is enabled, then say Y.
 678
 679 config ARCH_HAS_HMM
 680         bool
 681         default y
 682         depends on (X86_64 || PPC64)
 683         depends on ZONE_DEVICE
 684         depends on MMU && 64BIT
 685         depends on MEMORY_HOTPLUG
 686         depends on MEMORY_HOTREMOVE
 687         depends on SPARSEMEM_VMEMMAP
 688
 689 config MIGRATE_VMA_HELPER
 690         bool
 691
 692 config DEV_PAGEMAP_OPS
 693         bool
 694
 695 config HMM
 696         bool
 697         select MIGRATE_VMA_HELPER
 698
 699 config HMM_MIRROR
 700         bool "HMM mirror CPU page table into a device page table"
 701         depends on ARCH_HAS_HMM
 702         select MMU_NOTIFIER
 703         select HMM
 704         help
 705           Select HMM_MIRROR if you want to mirror range of the CPU page table of a
 706           process into a device page table. Here, mirror means "keep synchronized".
 707           Prerequisites: the device must provide the ability to write-protect its
 708           page tables (at PAGE_SIZE granularity), and must be able to recover from
 709           the resulting potential page faults.
 710
 711 config DEVICE_PRIVATE
 712         bool "Unaddressable device memory (GPU memory, ...)"
 713         depends on ARCH_HAS_HMM
 714         select HMM
 715         select DEV_PAGEMAP_OPS
 716
 717         help
 718           Allows creation of struct pages to represent unaddressable device
 719           memory; i.e., memory that is only accessible from the device (or
 720           group of devices). You likely also want to select HMM_MIRROR.
 721
 722 config DEVICE_PUBLIC
 723         bool "Addressable device memory (like GPU memory)"
 724         depends on ARCH_HAS_HMM
 725         select HMM
 726         select DEV_PAGEMAP_OPS
 727
 728         help
 729           Allows creation of struct pages to represent addressable device
 730           memory; i.e., memory that is accessible from both the device and
 731           the CPU
 732
 733 config FRAME_VECTOR
 734         bool
 735
 736 config ARCH_USES_HIGH_VMA_FLAGS
 737         bool
 738 config ARCH_HAS_PKEYS
 739         bool
 740
 741 config PERCPU_STATS
 742         bool "Collect percpu memory statistics"
 743         default n
 744         help
 745           This feature collects and exposes statistics via debugfs. The
 746           information includes global and per chunk statistics, which can
 747           be used to help understand percpu memory usage.
 748
 749 config GUP_BENCHMARK
 750         bool "Enable infrastructure for get_user_pages_fast() benchmarking"
 751         default n
 752         help
 753           Provides /sys/kernel/debug/gup_benchmark that helps with testing
 754           performance of get_user_pages_fast().
 755
 756           See tools/testing/selftests/vm/gup_benchmark.c
 757
 758 config ARCH_HAS_PTE_SPECIAL
 759         bool
 760
 761 endmenu