mm/Kconfig

   1 config SELECT_MEMORY_MODEL
   2         def_bool y
   3         depends on ARCH_SELECT_MEMORY_MODEL
   4
   5 choice
   6         prompt "Memory model"
   7         depends on SELECT_MEMORY_MODEL
   8         default DISCONTIGMEM_MANUAL if ARCH_DISCONTIGMEM_DEFAULT
   9         default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
  10         default FLATMEM_MANUAL
  11
  12 config FLATMEM_MANUAL
  13         bool "Flat Memory"
  14         depends on !(ARCH_DISCONTIGMEM_ENABLE || ARCH_SPARSEMEM_ENABLE) || ARCH_FLATMEM_ENABLE
  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: FLATMEM.  This is normal
  19           and a correct option.
  20
  21           Some users of more advanced features like NUMA and
  22           memory hotplug may have different options here.
  23           DISCONTIGMEM is a more mature, better tested system,
  24           but is incompatible with memory hotplug and may suffer
  25           decreased performance over SPARSEMEM.  If unsure between
  26           "Sparse Memory" and "Discontiguous Memory", choose
  27           "Discontiguous Memory".
  28
  29           If unsure, choose this option (Flat Memory) over any other.
  30
  31 config DISCONTIGMEM_MANUAL
  32         bool "Discontiguous Memory"
  33         depends on ARCH_DISCONTIGMEM_ENABLE
  34         help
  35           This option provides enhanced support for discontiguous
  36           memory systems, over FLATMEM.  These systems have holes
  37           in their physical address spaces, and this option provides
  38           more efficient handling of these holes.  However, the vast
  39           majority of hardware has quite flat address spaces, and
  40           can have degraded performance from the extra overhead that
  41           this option imposes.
  42
  43           Many NUMA configurations will have this as the only option.
  44
  45           If unsure, choose "Flat Memory" over this option.
  46
  47 config SPARSEMEM_MANUAL
  48         bool "Sparse Memory"
  49         depends on ARCH_SPARSEMEM_ENABLE
  50         help
  51           This will be the only option for some systems, including
  52           memory hotplug systems.  This is normal.
  53
  54           For many other systems, this will be an alternative to
  55           "Discontiguous Memory".  This option provides some potential
  56           performance benefits, along with decreased code complexity,
  57           but it is newer, and more experimental.
  58
  59           If unsure, choose "Discontiguous Memory" or "Flat Memory"
  60           over this option.
  61
  62 endchoice
  63
  64 config DISCONTIGMEM
  65         def_bool y
  66         depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
  67
  68 config SPARSEMEM
  69         def_bool y
  70         depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
  71
  72 config FLATMEM
  73         def_bool y
  74         depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
  75
  76 config FLAT_NODE_MEM_MAP
  77         def_bool y
  78         depends on !SPARSEMEM
  79
  80 #
  81 # Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's
  82 # to represent different areas of memory.  This variable allows
  83 # those dependencies to exist individually.
  84 #
  85 config NEED_MULTIPLE_NODES
  86         def_bool y
  87         depends on DISCONTIGMEM || NUMA
  88
  89 config HAVE_MEMORY_PRESENT
  90         def_bool y
  91         depends on ARCH_HAVE_MEMORY_PRESENT || SPARSEMEM
  92
  93 #
  94 # SPARSEMEM_EXTREME (which is the default) does some bootmem
  95 # allocations when memory_present() is called.  If this cannot
  96 # be done on your architecture, select this option.  However,
  97 # statically allocating the mem_section[] array can potentially
  98 # consume vast quantities of .bss, so be careful.
  99 #
 100 # This option will also potentially produce smaller runtime code
 101 # with gcc 3.4 and later.
 102 #
 103 config SPARSEMEM_STATIC
 104         bool
 105
 106 #
 107 # Architecture platforms which require a two level mem_section in SPARSEMEM
 108 # must select this option. This is usually for architecture platforms with
 109 # an extremely sparse physical address space.
 110 #
 111 config SPARSEMEM_EXTREME
 112         def_bool y
 113         depends on SPARSEMEM && !SPARSEMEM_STATIC
 114
 115 config SPARSEMEM_VMEMMAP_ENABLE
 116         bool
 117
 118 config SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
 119         def_bool y
 120         depends on SPARSEMEM && X86_64
 121
 122 config SPARSEMEM_VMEMMAP
 123         bool "Sparse Memory virtual memmap"
 124         depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
 125         default y
 126         help
 127          SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
 128          pfn_to_page and page_to_pfn operations.  This is the most
 129          efficient option when sufficient kernel resources are available.
 130
 131 config HAVE_MEMBLOCK
 132         bool
 133
 134 config HAVE_MEMBLOCK_NODE_MAP
 135         bool
 136
 137 config HAVE_MEMBLOCK_PHYS_MAP
 138         bool
 139
 140 config HAVE_GENERIC_GUP
 141         bool
 142
 143 config ARCH_DISCARD_MEMBLOCK
 144         bool
 145
 146 config NO_BOOTMEM
 147         bool
 148
 149 config MEMORY_ISOLATION
 150         bool
 151
 152 #
 153 # Only be set on architectures that have completely implemented memory hotplug
 154 # feature. If you are not sure, don't touch it.
 155 #
 156 config HAVE_BOOTMEM_INFO_NODE
 157         def_bool n
 158
 159 # eventually, we can have this option just 'select SPARSEMEM'
 160 config MEMORY_HOTPLUG
 161         bool "Allow for memory hot-add"
 162         depends on SPARSEMEM || X86_64_ACPI_NUMA
 163         depends on ARCH_ENABLE_MEMORY_HOTPLUG
 164
 165 config MEMORY_HOTPLUG_SPARSE
 166         def_bool y
 167         depends on SPARSEMEM && MEMORY_HOTPLUG
 168
 169 config MEMORY_HOTPLUG_DEFAULT_ONLINE
 170         bool "Online the newly added memory blocks by default"
 171         default n
 172         depends on MEMORY_HOTPLUG
 173         help
 174           This option sets the default policy setting for memory hotplug
 175           onlining policy (/sys/devices/system/memory/auto_online_blocks) which
 176           determines what happens to newly added memory regions. Policy setting
 177           can always be changed at runtime.
 178           See Documentation/memory-hotplug.txt for more information.
 179
 180           Say Y here if you want all hot-plugged memory blocks to appear in
 181           'online' state by default.
 182           Say N here if you want the default policy to keep all hot-plugged
 183           memory blocks in 'offline' state.
 184
 185 config MEMORY_HOTREMOVE
 186         bool "Allow for memory hot remove"
 187         select MEMORY_ISOLATION
 188         select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
 189         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 190         depends on MIGRATION
 191
 192 # Heavily threaded applications may benefit from splitting the mm-wide
 193 # page_table_lock, so that faults on different parts of the user address
 194 # space can be handled with less contention: split it at this NR_CPUS.
 195 # Default to 4 for wider testing, though 8 might be more appropriate.
 196 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 197 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 198 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 199 #
 200 config SPLIT_PTLOCK_CPUS
 201         int
 202         default "999999" if !MMU
 203         default "999999" if ARM && !CPU_CACHE_VIPT
 204         default "999999" if PARISC && !PA20
 205         default "4"
 206
 207 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
 208         bool
 209
 210 #
 211 # support for memory balloon
 212 config MEMORY_BALLOON
 213         bool
 214
 215 #
 216 # support for memory balloon compaction
 217 config BALLOON_COMPACTION
 218         bool "Allow for balloon memory compaction/migration"
 219         def_bool y
 220         depends on COMPACTION && MEMORY_BALLOON
 221         help
 222           Memory fragmentation introduced by ballooning might reduce
 223           significantly the number of 2MB contiguous memory blocks that can be
 224           used within a guest, thus imposing performance penalties associated
 225           with the reduced number of transparent huge pages that could be used
 226           by the guest workload. Allowing the compaction & migration for memory
 227           pages enlisted as being part of memory balloon devices avoids the
 228           scenario aforementioned and helps improving memory defragmentation.
 229
 230 #
 231 # support for memory compaction
 232 config COMPACTION
 233         bool "Allow for memory compaction"
 234         def_bool y
 235         select MIGRATION
 236         depends on MMU
 237         help
 238           Compaction is the only memory management component to form
 239           high order (larger physically contiguous) memory blocks
 240           reliably. The page allocator relies on compaction heavily and
 241           the lack of the feature can lead to unexpected OOM killer
 242           invocations for high order memory requests. You shouldn't
 243           disable this option unless there really is a strong reason for
 244           it and then we would be really interested to hear about that at
 245           linux-mm@kvack.org.
 246
 247 #
 248 # support for page migration
 249 #
 250 config MIGRATION
 251         bool "Page migration"
 252         def_bool y
 253         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
 254         help
 255           Allows the migration of the physical location of pages of processes
 256           while the virtual addresses are not changed. This is useful in
 257           two situations. The first is on NUMA systems to put pages nearer
 258           to the processors accessing. The second is when allocating huge
 259           pages as migration can relocate pages to satisfy a huge page
 260           allocation instead of reclaiming.
 261
 262 config ARCH_ENABLE_HUGEPAGE_MIGRATION
 263         bool
 264
 265 config ARCH_ENABLE_THP_MIGRATION
 266         bool
 267
 268 config PHYS_ADDR_T_64BIT
 269         def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
 270
 271 config BOUNCE
 272         bool "Enable bounce buffers"
 273         default y
 274         depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 275         help
 276           Enable bounce buffers for devices that cannot access
 277           the full range of memory available to the CPU. Enabled
 278           by default when ZONE_DMA or HIGHMEM is selected, but you
 279           may say n to override this.
 280
 281 # On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
 282 # have more than 4GB of memory, but we don't currently use the IOTLB to present
 283 # a 32-bit address to OHCI.  So we need to use a bounce pool instead.
 284 config NEED_BOUNCE_POOL
 285         bool
 286         default y if TILE && USB_OHCI_HCD
 287
 288 config NR_QUICK
 289         int
 290         depends on QUICKLIST
 291         default "1"
 292
 293 config VIRT_TO_BUS
 294         bool
 295         help
 296           An architecture should select this if it implements the
 297           deprecated interface virt_to_bus().  All new architectures
 298           should probably not select this.
 299
 300
 301 config MMU_NOTIFIER
 302         bool
 303         select SRCU
 304
 305 config KSM
 306         bool "Enable KSM for page merging"
 307         depends on MMU
 308         help
 309           Enable Kernel Samepage Merging: KSM periodically scans those areas
 310           of an application's address space that an app has advised may be
 311           mergeable.  When it finds pages of identical content, it replaces
 312           the many instances by a single page with that content, so
 313           saving memory until one or another app needs to modify the content.
 314           Recommended for use with KVM, or with other duplicative applications.
 315           See Documentation/vm/ksm.txt for more information: KSM is inactive
 316           until a program has madvised that an area is MADV_MERGEABLE, and
 317           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 318
 319 config DEFAULT_MMAP_MIN_ADDR
 320         int "Low address space to protect from user allocation"
 321         depends on MMU
 322         default 4096
 323         help
 324           This is the portion of low virtual memory which should be protected
 325           from userspace allocation.  Keeping a user from writing to low pages
 326           can help reduce the impact of kernel NULL pointer bugs.
 327
 328           For most ia64, ppc64 and x86 users with lots of address space
 329           a value of 65536 is reasonable and should cause no problems.
 330           On arm and other archs it should not be higher than 32768.
 331           Programs which use vm86 functionality or have some need to map
 332           this low address space will need CAP_SYS_RAWIO or disable this
 333           protection by setting the value to 0.
 334
 335           This value can be changed after boot using the
 336           /proc/sys/vm/mmap_min_addr tunable.
 337
 338 config ARCH_SUPPORTS_MEMORY_FAILURE
 339         bool
 340
 341 config MEMORY_FAILURE
 342         depends on MMU
 343         depends on ARCH_SUPPORTS_MEMORY_FAILURE
 344         bool "Enable recovery from hardware memory errors"
 345         select MEMORY_ISOLATION
 346         select RAS
 347         help
 348           Enables code to recover from some memory failures on systems
 349           with MCA recovery. This allows a system to continue running
 350           even when some of its memory has uncorrected errors. This requires
 351           special hardware support and typically ECC memory.
 352
 353 config HWPOISON_INJECT
 354         tristate "HWPoison pages injector"
 355         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 356         select PROC_PAGE_MONITOR
 357
 358 config NOMMU_INITIAL_TRIM_EXCESS
 359         int "Turn on mmap() excess space trimming before booting"
 360         depends on !MMU
 361         default 1
 362         help
 363           The NOMMU mmap() frequently needs to allocate large contiguous chunks
 364           of memory on which to store mappings, but it can only ask the system
 365           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 366           more than it requires.  To deal with this, mmap() is able to trim off
 367           the excess and return it to the allocator.
 368
 369           If trimming is enabled, the excess is trimmed off and returned to the
 370           system allocator, which can cause extra fragmentation, particularly
 371           if there are a lot of transient processes.
 372
 373           If trimming is disabled, the excess is kept, but not used, which for
 374           long-term mappings means that the space is wasted.
 375
 376           Trimming can be dynamically controlled through a sysctl option
 377           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 378           excess pages there must be before trimming should occur, or zero if
 379           no trimming is to occur.
 380
 381           This option specifies the initial value of this option.  The default
 382           of 1 says that all excess pages should be trimmed.
 383
 384           See Documentation/nommu-mmap.txt for more information.
 385
 386 config TRANSPARENT_HUGEPAGE
 387         bool "Transparent Hugepage Support"
 388         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 389         select COMPACTION
 390         select RADIX_TREE_MULTIORDER
 391         help
 392           Transparent Hugepages allows the kernel to use huge pages and
 393           huge tlb transparently to the applications whenever possible.
 394           This feature can improve computing performance to certain
 395           applications by speeding up page faults during memory
 396           allocation, by reducing the number of tlb misses and by speeding
 397           up the pagetable walking.
 398
 399           If memory constrained on embedded, you may want to say N.
 400
 401 choice
 402         prompt "Transparent Hugepage Support sysfs defaults"
 403         depends on TRANSPARENT_HUGEPAGE
 404         default TRANSPARENT_HUGEPAGE_ALWAYS
 405         help
 406           Selects the sysfs defaults for Transparent Hugepage Support.
 407
 408         config TRANSPARENT_HUGEPAGE_ALWAYS
 409                 bool "always"
 410         help
 411           Enabling Transparent Hugepage always, can increase the
 412           memory footprint of applications without a guaranteed
 413           benefit but it will work automatically for all applications.
 414
 415         config TRANSPARENT_HUGEPAGE_MADVISE
 416                 bool "madvise"
 417         help
 418           Enabling Transparent Hugepage madvise, will only provide a
 419           performance improvement benefit to the applications using
 420           madvise(MADV_HUGEPAGE) but it won't risk to increase the
 421           memory footprint of applications without a guaranteed
 422           benefit.
 423 endchoice
 424
 425 config ARCH_WANTS_THP_SWAP
 426        def_bool n
 427
 428 config THP_SWAP
 429         def_bool y
 430         depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP
 431         help
 432           Swap transparent huge pages in one piece, without splitting.
 433           XXX: For now this only does clustered swap space allocation.
 434
 435           For selection by architectures with reasonable THP sizes.
 436
 437 config  TRANSPARENT_HUGE_PAGECACHE
 438         def_bool y
 439         depends on TRANSPARENT_HUGEPAGE
 440
 441 #
 442 # UP and nommu archs use km based percpu allocator
 443 #
 444 config NEED_PER_CPU_KM
 445         depends on !SMP
 446         bool
 447         default y
 448
 449 config CLEANCACHE
 450         bool "Enable cleancache driver to cache clean pages if tmem is present"
 451         default n
 452         help
 453           Cleancache can be thought of as a page-granularity victim cache
 454           for clean pages that the kernel's pageframe replacement algorithm
 455           (PFRA) would like to keep around, but can't since there isn't enough
 456           memory.  So when the PFRA "evicts" a page, it first attempts to use
 457           cleancache code to put the data contained in that page into
 458           "transcendent memory", memory that is not directly accessible or
 459           addressable by the kernel and is of unknown and possibly
 460           time-varying size.  And when a cleancache-enabled
 461           filesystem wishes to access a page in a file on disk, it first
 462           checks cleancache to see if it already contains it; if it does,
 463           the page is copied into the kernel and a disk access is avoided.
 464           When a transcendent memory driver is available (such as zcache or
 465           Xen transcendent memory), a significant I/O reduction
 466           may be achieved.  When none is available, all cleancache calls
 467           are reduced to a single pointer-compare-against-NULL resulting
 468           in a negligible performance hit.
 469
 470           If unsure, say Y to enable cleancache
 471
 472 config FRONTSWAP
 473         bool "Enable frontswap to cache swap pages if tmem is present"
 474         depends on SWAP
 475         default n
 476         help
 477           Frontswap is so named because it can be thought of as the opposite
 478           of a "backing" store for a swap device.  The data is stored into
 479           "transcendent memory", memory that is not directly accessible or
 480           addressable by the kernel and is of unknown and possibly
 481           time-varying size.  When space in transcendent memory is available,
 482           a significant swap I/O reduction may be achieved.  When none is
 483           available, all frontswap calls are reduced to a single pointer-
 484           compare-against-NULL resulting in a negligible performance hit
 485           and swap data is stored as normal on the matching swap device.
 486
 487           If unsure, say Y to enable frontswap.
 488
 489 config CMA
 490         bool "Contiguous Memory Allocator"
 491         depends on HAVE_MEMBLOCK && MMU
 492         select MIGRATION
 493         select MEMORY_ISOLATION
 494         help
 495           This enables the Contiguous Memory Allocator which allows other
 496           subsystems to allocate big physically-contiguous blocks of memory.
 497           CMA reserves a region of memory and allows only movable pages to
 498           be allocated from it. This way, the kernel can use the memory for
 499           pagecache and when a subsystem requests for contiguous area, the
 500           allocated pages are migrated away to serve the contiguous request.
 501
 502           If unsure, say "n".
 503
 504 config CMA_DEBUG
 505         bool "CMA debug messages (DEVELOPMENT)"
 506         depends on DEBUG_KERNEL && CMA
 507         help
 508           Turns on debug messages in CMA.  This produces KERN_DEBUG
 509           messages for every CMA call as well as various messages while
 510           processing calls such as dma_alloc_from_contiguous().
 511           This option does not affect warning and error messages.
 512
 513 config CMA_DEBUGFS
 514         bool "CMA debugfs interface"
 515         depends on CMA && DEBUG_FS
 516         help
 517           Turns on the DebugFS interface for CMA.
 518
 519 config CMA_AREAS
 520         int "Maximum count of the CMA areas"
 521         depends on CMA
 522         default 7
 523         help
 524           CMA allows to create CMA areas for particular purpose, mainly,
 525           used as device private area. This parameter sets the maximum
 526           number of CMA area in the system.
 527
 528           If unsure, leave the default value "7".
 529
 530 config MEM_SOFT_DIRTY
 531         bool "Track memory changes"
 532         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
 533         select PROC_PAGE_MONITOR
 534         help
 535           This option enables memory changes tracking by introducing a
 536           soft-dirty bit on pte-s. This bit it set when someone writes
 537           into a page just as regular dirty bit, but unlike the latter
 538           it can be cleared by hands.
 539
 540           See Documentation/vm/soft-dirty.txt for more details.
 541
 542 config ZSWAP
 543         bool "Compressed cache for swap pages (EXPERIMENTAL)"
 544         depends on FRONTSWAP && CRYPTO=y
 545         select CRYPTO_LZO
 546         select ZPOOL
 547         default n
 548         help
 549           A lightweight compressed cache for swap pages.  It takes
 550           pages that are in the process of being swapped out and attempts to
 551           compress them into a dynamically allocated RAM-based memory pool.
 552           This can result in a significant I/O reduction on swap device and,
 553           in the case where decompressing from RAM is faster that swap device
 554           reads, can also improve workload performance.
 555
 556           This is marked experimental because it is a new feature (as of
 557           v3.11) that interacts heavily with memory reclaim.  While these
 558           interactions don't cause any known issues on simple memory setups,
 559           they have not be fully explored on the large set of potential
 560           configurations and workloads that exist.
 561
 562 config ZPOOL
 563         tristate "Common API for compressed memory storage"
 564         default n
 565         help
 566           Compressed memory storage API.  This allows using either zbud or
 567           zsmalloc.
 568
 569 config ZBUD
 570         tristate "Low (Up to 2x) density storage for compressed pages"
 571         default n
 572         help
 573           A special purpose allocator for storing compressed pages.
 574           It is designed to store up to two compressed pages per physical
 575           page.  While this design limits storage density, it has simple and
 576           deterministic reclaim properties that make it preferable to a higher
 577           density approach when reclaim will be used.
 578
 579 config Z3FOLD
 580         tristate "Up to 3x density storage for compressed pages"
 581         depends on ZPOOL
 582         default n
 583         help
 584           A special purpose allocator for storing compressed pages.
 585           It is designed to store up to three compressed pages per physical
 586           page. It is a ZBUD derivative so the simplicity and determinism are
 587           still there.
 588
 589 config ZSMALLOC
 590         tristate "Memory allocator for compressed pages"
 591         depends on MMU
 592         default n
 593         help
 594           zsmalloc is a slab-based memory allocator designed to store
 595           compressed RAM pages.  zsmalloc uses virtual memory mapping
 596           in order to reduce fragmentation.  However, this results in a
 597           non-standard allocator interface where a handle, not a pointer, is
 598           returned by an alloc().  This handle must be mapped in order to
 599           access the allocated space.
 600
 601 config PGTABLE_MAPPING
 602         bool "Use page table mapping to access object in zsmalloc"
 603         depends on ZSMALLOC
 604         help
 605           By default, zsmalloc uses a copy-based object mapping method to
 606           access allocations that span two pages. However, if a particular
 607           architecture (ex, ARM) performs VM mapping faster than copying,
 608           then you should select this. This causes zsmalloc to use page table
 609           mapping rather than copying for object mapping.
 610
 611           You can check speed with zsmalloc benchmark:
 612           https://github.com/spartacus06/zsmapbench
 613
 614 config ZSMALLOC_STAT
 615         bool "Export zsmalloc statistics"
 616         depends on ZSMALLOC
 617         select DEBUG_FS
 618         help
 619           This option enables code in the zsmalloc to collect various
 620           statistics about whats happening in zsmalloc and exports that
 621           information to userspace via debugfs.
 622           If unsure, say N.
 623
 624 config GENERIC_EARLY_IOREMAP
 625         bool
 626
 627 config MAX_STACK_SIZE_MB
 628         int "Maximum user stack size for 32-bit processes (MB)"
 629         default 80
 630         range 8 256 if METAG
 631         range 8 2048
 632         depends on STACK_GROWSUP && (!64BIT || COMPAT)
 633         help
 634           This is the maximum stack size in Megabytes in the VM layout of 32-bit
 635           user processes when the stack grows upwards (currently only on parisc
 636           and metag arch). The stack will be located at the highest memory
 637           address minus the given value, unless the RLIMIT_STACK hard limit is
 638           changed to a smaller value in which case that is used.
 639
 640           A sane initial value is 80 MB.
 641
 642 # For architectures that support deferred memory initialisation
 643 config ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
 644         bool
 645
 646 config DEFERRED_STRUCT_PAGE_INIT
 647         bool "Defer initialisation of struct pages to kthreads"
 648         default n
 649         depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
 650         depends on NO_BOOTMEM && MEMORY_HOTPLUG
 651         depends on !FLATMEM
 652         depends on !NEED_PER_CPU_KM
 653         help
 654           Ordinarily all struct pages are initialised during early boot in a
 655           single thread. On very large machines this can take a considerable
 656           amount of time. If this option is set, large machines will bring up
 657           a subset of memmap at boot and then initialise the rest in parallel
 658           by starting one-off "pgdatinitX" kernel thread for each node X. This
 659           has a potential performance impact on processes running early in the
 660           lifetime of the system until these kthreads finish the
 661           initialisation.
 662
 663 config IDLE_PAGE_TRACKING
 664         bool "Enable idle page tracking"
 665         depends on SYSFS && MMU
 666         select PAGE_EXTENSION if !64BIT
 667         help
 668           This feature allows to estimate the amount of user pages that have
 669           not been touched during a given period of time. This information can
 670           be useful to tune memory cgroup limits and/or for job placement
 671           within a compute cluster.
 672
 673           See Documentation/vm/idle_page_tracking.txt for more details.
 674
 675 # arch_add_memory() comprehends device memory
 676 config ARCH_HAS_ZONE_DEVICE
 677         bool
 678
 679 config ZONE_DEVICE
 680         bool "Device memory (pmem, HMM, etc...) hotplug support"
 681         depends on MEMORY_HOTPLUG
 682         depends on MEMORY_HOTREMOVE
 683         depends on SPARSEMEM_VMEMMAP
 684         depends on ARCH_HAS_ZONE_DEVICE
 685         select RADIX_TREE_MULTIORDER
 686
 687         help
 688           Device memory hotplug support allows for establishing pmem,
 689           or other device driver discovered memory regions, in the
 690           memmap. This allows pfn_to_page() lookups of otherwise
 691           "device-physical" addresses which is needed for using a DAX
 692           mapping in an O_DIRECT operation, among other things.
 693
 694           If FS_DAX is enabled, then say Y.
 695
 696 config ARCH_HAS_HMM
 697         bool
 698         default y
 699         depends on (X86_64 || PPC64)
 700         depends on ZONE_DEVICE
 701         depends on MMU && 64BIT
 702         depends on MEMORY_HOTPLUG
 703         depends on MEMORY_HOTREMOVE
 704         depends on SPARSEMEM_VMEMMAP
 705
 706 config MIGRATE_VMA_HELPER
 707         bool
 708
 709 config HMM
 710         bool
 711         select MIGRATE_VMA_HELPER
 712
 713 config HMM_MIRROR
 714         bool "HMM mirror CPU page table into a device page table"
 715         depends on ARCH_HAS_HMM
 716         select MMU_NOTIFIER
 717         select HMM
 718         help
 719           Select HMM_MIRROR if you want to mirror range of the CPU page table of a
 720           process into a device page table. Here, mirror means "keep synchronized".
 721           Prerequisites: the device must provide the ability to write-protect its
 722           page tables (at PAGE_SIZE granularity), and must be able to recover from
 723           the resulting potential page faults.
 724
 725 config DEVICE_PRIVATE
 726         bool "Unaddressable device memory (GPU memory, ...)"
 727         depends on ARCH_HAS_HMM
 728         select HMM
 729
 730         help
 731           Allows creation of struct pages to represent unaddressable device
 732           memory; i.e., memory that is only accessible from the device (or
 733           group of devices). You likely also want to select HMM_MIRROR.
 734
 735 config DEVICE_PUBLIC
 736         bool "Addressable device memory (like GPU memory)"
 737         depends on ARCH_HAS_HMM
 738         select HMM
 739
 740         help
 741           Allows creation of struct pages to represent addressable device
 742           memory; i.e., memory that is accessible from both the device and
 743           the CPU
 744
 745 config FRAME_VECTOR
 746         bool
 747
 748 config ARCH_USES_HIGH_VMA_FLAGS
 749         bool
 750 config ARCH_HAS_PKEYS
 751         bool
 752
 753 config PERCPU_STATS
 754         bool "Collect percpu memory statistics"
 755         default n
 756         help
 757           This feature collects and exposes statistics via debugfs. The
 758           information includes global and per chunk statistics, which can
 759           be used to help understand percpu memory usage.
 760
 761 config GUP_BENCHMARK
 762         bool "Enable infrastructure for get_user_pages_fast() benchmarking"
 763         default n
 764         help
 765           Provides /sys/kernel/debug/gup_benchmark that helps with testing
 766           performance of get_user_pages_fast().
 767
 768           See tools/testing/selftests/vm/gup_benchmark.c