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         help
 295           Enable Kernel Samepage Merging: KSM periodically scans those areas
 296           of an application's address space that an app has advised may be
 297           mergeable.  When it finds pages of identical content, it replaces
 298           the many instances by a single page with that content, so
 299           saving memory until one or another app needs to modify the content.
 300           Recommended for use with KVM, or with other duplicative applications.
 301           See Documentation/vm/ksm.rst for more information: KSM is inactive
 302           until a program has madvised that an area is MADV_MERGEABLE, and
 303           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 304
 305 config DEFAULT_MMAP_MIN_ADDR
 306         int "Low address space to protect from user allocation"
 307         depends on MMU
 308         default 4096
 309         help
 310           This is the portion of low virtual memory which should be protected
 311           from userspace allocation.  Keeping a user from writing to low pages
 312           can help reduce the impact of kernel NULL pointer bugs.
 313
 314           For most ia64, ppc64 and x86 users with lots of address space
 315           a value of 65536 is reasonable and should cause no problems.
 316           On arm and other archs it should not be higher than 32768.
 317           Programs which use vm86 functionality or have some need to map
 318           this low address space will need CAP_SYS_RAWIO or disable this
 319           protection by setting the value to 0.
 320
 321           This value can be changed after boot using the
 322           /proc/sys/vm/mmap_min_addr tunable.
 323
 324 config ARCH_SUPPORTS_MEMORY_FAILURE
 325         bool
 326
 327 config MEMORY_FAILURE
 328         depends on MMU
 329         depends on ARCH_SUPPORTS_MEMORY_FAILURE
 330         bool "Enable recovery from hardware memory errors"
 331         select MEMORY_ISOLATION
 332         select RAS
 333         help
 334           Enables code to recover from some memory failures on systems
 335           with MCA recovery. This allows a system to continue running
 336           even when some of its memory has uncorrected errors. This requires
 337           special hardware support and typically ECC memory.
 338
 339 config HWPOISON_INJECT
 340         tristate "HWPoison pages injector"
 341         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 342         select PROC_PAGE_MONITOR
 343
 344 config NOMMU_INITIAL_TRIM_EXCESS
 345         int "Turn on mmap() excess space trimming before booting"
 346         depends on !MMU
 347         default 1
 348         help
 349           The NOMMU mmap() frequently needs to allocate large contiguous chunks
 350           of memory on which to store mappings, but it can only ask the system
 351           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 352           more than it requires.  To deal with this, mmap() is able to trim off
 353           the excess and return it to the allocator.
 354
 355           If trimming is enabled, the excess is trimmed off and returned to the
 356           system allocator, which can cause extra fragmentation, particularly
 357           if there are a lot of transient processes.
 358
 359           If trimming is disabled, the excess is kept, but not used, which for
 360           long-term mappings means that the space is wasted.
 361
 362           Trimming can be dynamically controlled through a sysctl option
 363           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 364           excess pages there must be before trimming should occur, or zero if
 365           no trimming is to occur.
 366
 367           This option specifies the initial value of this option.  The default
 368           of 1 says that all excess pages should be trimmed.
 369
 370           See Documentation/nommu-mmap.txt for more information.
 371
 372 config TRANSPARENT_HUGEPAGE
 373         bool "Transparent Hugepage Support"
 374         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 375         select COMPACTION
 376         select XARRAY_MULTI
 377         help
 378           Transparent Hugepages allows the kernel to use huge pages and
 379           huge tlb transparently to the applications whenever possible.
 380           This feature can improve computing performance to certain
 381           applications by speeding up page faults during memory
 382           allocation, by reducing the number of tlb misses and by speeding
 383           up the pagetable walking.
 384
 385           If memory constrained on embedded, you may want to say N.
 386
 387 choice
 388         prompt "Transparent Hugepage Support sysfs defaults"
 389         depends on TRANSPARENT_HUGEPAGE
 390         default TRANSPARENT_HUGEPAGE_ALWAYS
 391         help
 392           Selects the sysfs defaults for Transparent Hugepage Support.
 393
 394         config TRANSPARENT_HUGEPAGE_ALWAYS
 395                 bool "always"
 396         help
 397           Enabling Transparent Hugepage always, can increase the
 398           memory footprint of applications without a guaranteed
 399           benefit but it will work automatically for all applications.
 400
 401         config TRANSPARENT_HUGEPAGE_MADVISE
 402                 bool "madvise"
 403         help
 404           Enabling Transparent Hugepage madvise, will only provide a
 405           performance improvement benefit to the applications using
 406           madvise(MADV_HUGEPAGE) but it won't risk to increase the
 407           memory footprint of applications without a guaranteed
 408           benefit.
 409 endchoice
 410
 411 config ARCH_WANTS_THP_SWAP
 412        def_bool n
 413
 414 config THP_SWAP
 415         def_bool y
 416         depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP
 417         help
 418           Swap transparent huge pages in one piece, without splitting.
 419           XXX: For now, swap cluster backing transparent huge page
 420           will be split after swapout.
 421
 422           For selection by architectures with reasonable THP sizes.
 423
 424 config  TRANSPARENT_HUGE_PAGECACHE
 425         def_bool y
 426         depends on TRANSPARENT_HUGEPAGE
 427
 428 #
 429 # UP and nommu archs use km based percpu allocator
 430 #
 431 config NEED_PER_CPU_KM
 432         depends on !SMP
 433         bool
 434         default y
 435
 436 config CLEANCACHE
 437         bool "Enable cleancache driver to cache clean pages if tmem is present"
 438         default n
 439         help
 440           Cleancache can be thought of as a page-granularity victim cache
 441           for clean pages that the kernel's pageframe replacement algorithm
 442           (PFRA) would like to keep around, but can't since there isn't enough
 443           memory.  So when the PFRA "evicts" a page, it first attempts to use
 444           cleancache code to put the data contained in that page into
 445           "transcendent memory", memory that is not directly accessible or
 446           addressable by the kernel and is of unknown and possibly
 447           time-varying size.  And when a cleancache-enabled
 448           filesystem wishes to access a page in a file on disk, it first
 449           checks cleancache to see if it already contains it; if it does,
 450           the page is copied into the kernel and a disk access is avoided.
 451           When a transcendent memory driver is available (such as zcache or
 452           Xen transcendent memory), a significant I/O reduction
 453           may be achieved.  When none is available, all cleancache calls
 454           are reduced to a single pointer-compare-against-NULL resulting
 455           in a negligible performance hit.
 456
 457           If unsure, say Y to enable cleancache
 458
 459 config FRONTSWAP
 460         bool "Enable frontswap to cache swap pages if tmem is present"
 461         depends on SWAP
 462         default n
 463         help
 464           Frontswap is so named because it can be thought of as the opposite
 465           of a "backing" store for a swap device.  The data is stored into
 466           "transcendent memory", memory that is not directly accessible or
 467           addressable by the kernel and is of unknown and possibly
 468           time-varying size.  When space in transcendent memory is available,
 469           a significant swap I/O reduction may be achieved.  When none is
 470           available, all frontswap calls are reduced to a single pointer-
 471           compare-against-NULL resulting in a negligible performance hit
 472           and swap data is stored as normal on the matching swap device.
 473
 474           If unsure, say Y to enable frontswap.
 475
 476 config CMA
 477         bool "Contiguous Memory Allocator"
 478         depends on MMU
 479         select MIGRATION
 480         select MEMORY_ISOLATION
 481         help
 482           This enables the Contiguous Memory Allocator which allows other
 483           subsystems to allocate big physically-contiguous blocks of memory.
 484           CMA reserves a region of memory and allows only movable pages to
 485           be allocated from it. This way, the kernel can use the memory for
 486           pagecache and when a subsystem requests for contiguous area, the
 487           allocated pages are migrated away to serve the contiguous request.
 488
 489           If unsure, say "n".
 490
 491 config CMA_DEBUG
 492         bool "CMA debug messages (DEVELOPMENT)"
 493         depends on DEBUG_KERNEL && CMA
 494         help
 495           Turns on debug messages in CMA.  This produces KERN_DEBUG
 496           messages for every CMA call as well as various messages while
 497           processing calls such as dma_alloc_from_contiguous().
 498           This option does not affect warning and error messages.
 499
 500 config CMA_DEBUGFS
 501         bool "CMA debugfs interface"
 502         depends on CMA && DEBUG_FS
 503         help
 504           Turns on the DebugFS interface for CMA.
 505
 506 config CMA_AREAS
 507         int "Maximum count of the CMA areas"
 508         depends on CMA
 509         default 7
 510         help
 511           CMA allows to create CMA areas for particular purpose, mainly,
 512           used as device private area. This parameter sets the maximum
 513           number of CMA area in the system.
 514
 515           If unsure, leave the default value "7".
 516
 517 config MEM_SOFT_DIRTY
 518         bool "Track memory changes"
 519         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
 520         select PROC_PAGE_MONITOR
 521         help
 522           This option enables memory changes tracking by introducing a
 523           soft-dirty bit on pte-s. This bit it set when someone writes
 524           into a page just as regular dirty bit, but unlike the latter
 525           it can be cleared by hands.
 526
 527           See Documentation/admin-guide/mm/soft-dirty.rst for more details.
 528
 529 config ZSWAP
 530         bool "Compressed cache for swap pages (EXPERIMENTAL)"
 531         depends on FRONTSWAP && CRYPTO=y
 532         select CRYPTO_LZO
 533         select ZPOOL
 534         default n
 535         help
 536           A lightweight compressed cache for swap pages.  It takes
 537           pages that are in the process of being swapped out and attempts to
 538           compress them into a dynamically allocated RAM-based memory pool.
 539           This can result in a significant I/O reduction on swap device and,
 540           in the case where decompressing from RAM is faster that swap device
 541           reads, can also improve workload performance.
 542
 543           This is marked experimental because it is a new feature (as of
 544           v3.11) that interacts heavily with memory reclaim.  While these
 545           interactions don't cause any known issues on simple memory setups,
 546           they have not be fully explored on the large set of potential
 547           configurations and workloads that exist.
 548
 549 config ZPOOL
 550         tristate "Common API for compressed memory storage"
 551         default n
 552         help
 553           Compressed memory storage API.  This allows using either zbud or
 554           zsmalloc.
 555
 556 config ZBUD
 557         tristate "Low (Up to 2x) density storage for compressed pages"
 558         default n
 559         help
 560           A special purpose allocator for storing compressed pages.
 561           It is designed to store up to two compressed pages per physical
 562           page.  While this design limits storage density, it has simple and
 563           deterministic reclaim properties that make it preferable to a higher
 564           density approach when reclaim will be used.
 565
 566 config Z3FOLD
 567         tristate "Up to 3x density storage for compressed pages"
 568         depends on ZPOOL
 569         default n
 570         help
 571           A special purpose allocator for storing compressed pages.
 572           It is designed to store up to three compressed pages per physical
 573           page. It is a ZBUD derivative so the simplicity and determinism are
 574           still there.
 575
 576 config ZSMALLOC
 577         tristate "Memory allocator for compressed pages"
 578         depends on MMU
 579         default n
 580         help
 581           zsmalloc is a slab-based memory allocator designed to store
 582           compressed RAM pages.  zsmalloc uses virtual memory mapping
 583           in order to reduce fragmentation.  However, this results in a
 584           non-standard allocator interface where a handle, not a pointer, is
 585           returned by an alloc().  This handle must be mapped in order to
 586           access the allocated space.
 587
 588 config PGTABLE_MAPPING
 589         bool "Use page table mapping to access object in zsmalloc"
 590         depends on ZSMALLOC
 591         help
 592           By default, zsmalloc uses a copy-based object mapping method to
 593           access allocations that span two pages. However, if a particular
 594           architecture (ex, ARM) performs VM mapping faster than copying,
 595           then you should select this. This causes zsmalloc to use page table
 596           mapping rather than copying for object mapping.
 597
 598           You can check speed with zsmalloc benchmark:
 599           https://github.com/spartacus06/zsmapbench
 600
 601 config ZSMALLOC_STAT
 602         bool "Export zsmalloc statistics"
 603         depends on ZSMALLOC
 604         select DEBUG_FS
 605         help
 606           This option enables code in the zsmalloc to collect various
 607           statistics about whats happening in zsmalloc and exports that
 608           information to userspace via debugfs.
 609           If unsure, say N.
 610
 611 config GENERIC_EARLY_IOREMAP
 612         bool
 613
 614 config MAX_STACK_SIZE_MB
 615         int "Maximum user stack size for 32-bit processes (MB)"
 616         default 80
 617         range 8 2048
 618         depends on STACK_GROWSUP && (!64BIT || COMPAT)
 619         help
 620           This is the maximum stack size in Megabytes in the VM layout of 32-bit
 621           user processes when the stack grows upwards (currently only on parisc
 622           arch). The stack will be located at the highest memory address minus
 623           the given value, unless the RLIMIT_STACK hard limit is changed to a
 624           smaller value in which case that is used.
 625
 626           A sane initial value is 80 MB.
 627
 628 config DEFERRED_STRUCT_PAGE_INIT
 629         bool "Defer initialisation of struct pages to kthreads"
 630         default n
 631         depends on SPARSEMEM
 632         depends on !NEED_PER_CPU_KM
 633         depends on 64BIT
 634         help
 635           Ordinarily all struct pages are initialised during early boot in a
 636           single thread. On very large machines this can take a considerable
 637           amount of time. If this option is set, large machines will bring up
 638           a subset of memmap at boot and then initialise the rest in parallel
 639           by starting one-off "pgdatinitX" kernel thread for each node X. This
 640           has a potential performance impact on processes running early in the
 641           lifetime of the system until these kthreads finish the
 642           initialisation.
 643
 644 config IDLE_PAGE_TRACKING
 645         bool "Enable idle page tracking"
 646         depends on SYSFS && MMU
 647         select PAGE_EXTENSION if !64BIT
 648         help
 649           This feature allows to estimate the amount of user pages that have
 650           not been touched during a given period of time. This information can
 651           be useful to tune memory cgroup limits and/or for job placement
 652           within a compute cluster.
 653
 654           See Documentation/admin-guide/mm/idle_page_tracking.rst for
 655           more details.
 656
 657 # arch_add_memory() comprehends device memory
 658 config ARCH_HAS_ZONE_DEVICE
 659         bool
 660
 661 config ZONE_DEVICE
 662         bool "Device memory (pmem, HMM, etc...) hotplug support"
 663         depends on MEMORY_HOTPLUG
 664         depends on MEMORY_HOTREMOVE
 665         depends on SPARSEMEM_VMEMMAP
 666         depends on ARCH_HAS_ZONE_DEVICE
 667         select XARRAY_MULTI
 668
 669         help
 670           Device memory hotplug support allows for establishing pmem,
 671           or other device driver discovered memory regions, in the
 672           memmap. This allows pfn_to_page() lookups of otherwise
 673           "device-physical" addresses which is needed for using a DAX
 674           mapping in an O_DIRECT operation, among other things.
 675
 676           If FS_DAX is enabled, then say Y.
 677
 678 config ARCH_HAS_HMM
 679         bool
 680         default y
 681         depends on (X86_64 || PPC64)
 682         depends on ZONE_DEVICE
 683         depends on MMU && 64BIT
 684         depends on MEMORY_HOTPLUG
 685         depends on MEMORY_HOTREMOVE
 686         depends on SPARSEMEM_VMEMMAP
 687
 688 config MIGRATE_VMA_HELPER
 689         bool
 690
 691 config DEV_PAGEMAP_OPS
 692         bool
 693
 694 config HMM
 695         bool
 696         select MIGRATE_VMA_HELPER
 697
 698 config HMM_MIRROR
 699         bool "HMM mirror CPU page table into a device page table"
 700         depends on ARCH_HAS_HMM
 701         select MMU_NOTIFIER
 702         select HMM
 703         help
 704           Select HMM_MIRROR if you want to mirror range of the CPU page table of a
 705           process into a device page table. Here, mirror means "keep synchronized".
 706           Prerequisites: the device must provide the ability to write-protect its
 707           page tables (at PAGE_SIZE granularity), and must be able to recover from
 708           the resulting potential page faults.
 709
 710 config DEVICE_PRIVATE
 711         bool "Unaddressable device memory (GPU memory, ...)"
 712         depends on ARCH_HAS_HMM
 713         select HMM
 714         select DEV_PAGEMAP_OPS
 715
 716         help
 717           Allows creation of struct pages to represent unaddressable device
 718           memory; i.e., memory that is only accessible from the device (or
 719           group of devices). You likely also want to select HMM_MIRROR.
 720
 721 config DEVICE_PUBLIC
 722         bool "Addressable device memory (like GPU memory)"
 723         depends on ARCH_HAS_HMM
 724         select HMM
 725         select DEV_PAGEMAP_OPS
 726
 727         help
 728           Allows creation of struct pages to represent addressable device
 729           memory; i.e., memory that is accessible from both the device and
 730           the CPU
 731
 732 config FRAME_VECTOR
 733         bool
 734
 735 config ARCH_USES_HIGH_VMA_FLAGS
 736         bool
 737 config ARCH_HAS_PKEYS
 738         bool
 739
 740 config PERCPU_STATS
 741         bool "Collect percpu memory statistics"
 742         default n
 743         help
 744           This feature collects and exposes statistics via debugfs. The
 745           information includes global and per chunk statistics, which can
 746           be used to help understand percpu memory usage.
 747
 748 config GUP_BENCHMARK
 749         bool "Enable infrastructure for get_user_pages_fast() benchmarking"
 750         default n
 751         help
 752           Provides /sys/kernel/debug/gup_benchmark that helps with testing
 753           performance of get_user_pages_fast().
 754
 755           See tools/testing/selftests/vm/gup_benchmark.c
 756
 757 config ARCH_HAS_PTE_SPECIAL
 758         bool
 759
 760 endmenu