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_RCU_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 config MOVABLE_NODE
 153         bool "Enable to assign a node which has only movable memory"
 154         depends on HAVE_MEMBLOCK
 155         depends on NO_BOOTMEM
 156         depends on X86_64
 157         depends on NUMA
 158         default n
 159         help
 160           Allow a node to have only movable memory.  Pages used by the kernel,
 161           such as direct mapping pages cannot be migrated.  So the corresponding
 162           memory device cannot be hotplugged.  This option allows the following
 163           two things:
 164           - When the system is booting, node full of hotpluggable memory can
 165           be arranged to have only movable memory so that the whole node can
 166           be hot-removed. (need movable_node boot option specified).
 167           - After the system is up, the option allows users to online all the
 168           memory of a node as movable memory so that the whole node can be
 169           hot-removed.
 170
 171           Users who don't use the memory hotplug feature are fine with this
 172           option on since they don't specify movable_node boot option or they
 173           don't online memory as movable.
 174
 175           Say Y here if you want to hotplug a whole node.
 176           Say N here if you want kernel to use memory on all nodes evenly.
 177
 178 #
 179 # Only be set on architectures that have completely implemented memory hotplug
 180 # feature. If you are not sure, don't touch it.
 181 #
 182 config HAVE_BOOTMEM_INFO_NODE
 183         def_bool n
 184
 185 # eventually, we can have this option just 'select SPARSEMEM'
 186 config MEMORY_HOTPLUG
 187         bool "Allow for memory hot-add"
 188         depends on SPARSEMEM || X86_64_ACPI_NUMA
 189         depends on ARCH_ENABLE_MEMORY_HOTPLUG
 190
 191 config MEMORY_HOTPLUG_SPARSE
 192         def_bool y
 193         depends on SPARSEMEM && MEMORY_HOTPLUG
 194
 195 config MEMORY_HOTPLUG_DEFAULT_ONLINE
 196         bool "Online the newly added memory blocks by default"
 197         default n
 198         depends on MEMORY_HOTPLUG
 199         help
 200           This option sets the default policy setting for memory hotplug
 201           onlining policy (/sys/devices/system/memory/auto_online_blocks) which
 202           determines what happens to newly added memory regions. Policy setting
 203           can always be changed at runtime.
 204           See Documentation/memory-hotplug.txt for more information.
 205
 206           Say Y here if you want all hot-plugged memory blocks to appear in
 207           'online' state by default.
 208           Say N here if you want the default policy to keep all hot-plugged
 209           memory blocks in 'offline' state.
 210
 211 config MEMORY_HOTREMOVE
 212         bool "Allow for memory hot remove"
 213         select MEMORY_ISOLATION
 214         select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
 215         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 216         depends on MIGRATION
 217
 218 # Heavily threaded applications may benefit from splitting the mm-wide
 219 # page_table_lock, so that faults on different parts of the user address
 220 # space can be handled with less contention: split it at this NR_CPUS.
 221 # Default to 4 for wider testing, though 8 might be more appropriate.
 222 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 223 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 224 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 225 #
 226 config SPLIT_PTLOCK_CPUS
 227         int
 228         default "999999" if !MMU
 229         default "999999" if ARM && !CPU_CACHE_VIPT
 230         default "999999" if PARISC && !PA20
 231         default "4"
 232
 233 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
 234         bool
 235
 236 #
 237 # support for memory balloon
 238 config MEMORY_BALLOON
 239         bool
 240
 241 #
 242 # support for memory balloon compaction
 243 config BALLOON_COMPACTION
 244         bool "Allow for balloon memory compaction/migration"
 245         def_bool y
 246         depends on COMPACTION && MEMORY_BALLOON
 247         help
 248           Memory fragmentation introduced by ballooning might reduce
 249           significantly the number of 2MB contiguous memory blocks that can be
 250           used within a guest, thus imposing performance penalties associated
 251           with the reduced number of transparent huge pages that could be used
 252           by the guest workload. Allowing the compaction & migration for memory
 253           pages enlisted as being part of memory balloon devices avoids the
 254           scenario aforementioned and helps improving memory defragmentation.
 255
 256 #
 257 # support for memory compaction
 258 config COMPACTION
 259         bool "Allow for memory compaction"
 260         def_bool y
 261         select MIGRATION
 262         depends on MMU
 263         help
 264           Allows the compaction of memory for the allocation of huge pages.
 265
 266 #
 267 # support for page migration
 268 #
 269 config MIGRATION
 270         bool "Page migration"
 271         def_bool y
 272         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
 273         help
 274           Allows the migration of the physical location of pages of processes
 275           while the virtual addresses are not changed. This is useful in
 276           two situations. The first is on NUMA systems to put pages nearer
 277           to the processors accessing. The second is when allocating huge
 278           pages as migration can relocate pages to satisfy a huge page
 279           allocation instead of reclaiming.
 280
 281 config ARCH_ENABLE_HUGEPAGE_MIGRATION
 282         bool
 283
 284 config PHYS_ADDR_T_64BIT
 285         def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
 286
 287 config BOUNCE
 288         bool "Enable bounce buffers"
 289         default y
 290         depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 291         help
 292           Enable bounce buffers for devices that cannot access
 293           the full range of memory available to the CPU. Enabled
 294           by default when ZONE_DMA or HIGHMEM is selected, but you
 295           may say n to override this.
 296
 297 # On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
 298 # have more than 4GB of memory, but we don't currently use the IOTLB to present
 299 # a 32-bit address to OHCI.  So we need to use a bounce pool instead.
 300 config NEED_BOUNCE_POOL
 301         bool
 302         default y if TILE && USB_OHCI_HCD
 303
 304 config NR_QUICK
 305         int
 306         depends on QUICKLIST
 307         default "2" if AVR32
 308         default "1"
 309
 310 config VIRT_TO_BUS
 311         bool
 312         help
 313           An architecture should select this if it implements the
 314           deprecated interface virt_to_bus().  All new architectures
 315           should probably not select this.
 316
 317
 318 config MMU_NOTIFIER
 319         bool
 320         select SRCU
 321
 322 config KSM
 323         bool "Enable KSM for page merging"
 324         depends on MMU
 325         help
 326           Enable Kernel Samepage Merging: KSM periodically scans those areas
 327           of an application's address space that an app has advised may be
 328           mergeable.  When it finds pages of identical content, it replaces
 329           the many instances by a single page with that content, so
 330           saving memory until one or another app needs to modify the content.
 331           Recommended for use with KVM, or with other duplicative applications.
 332           See Documentation/vm/ksm.txt for more information: KSM is inactive
 333           until a program has madvised that an area is MADV_MERGEABLE, and
 334           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 335
 336 config DEFAULT_MMAP_MIN_ADDR
 337         int "Low address space to protect from user allocation"
 338         depends on MMU
 339         default 4096
 340         help
 341           This is the portion of low virtual memory which should be protected
 342           from userspace allocation.  Keeping a user from writing to low pages
 343           can help reduce the impact of kernel NULL pointer bugs.
 344
 345           For most ia64, ppc64 and x86 users with lots of address space
 346           a value of 65536 is reasonable and should cause no problems.
 347           On arm and other archs it should not be higher than 32768.
 348           Programs which use vm86 functionality or have some need to map
 349           this low address space will need CAP_SYS_RAWIO or disable this
 350           protection by setting the value to 0.
 351
 352           This value can be changed after boot using the
 353           /proc/sys/vm/mmap_min_addr tunable.
 354
 355 config ARCH_SUPPORTS_MEMORY_FAILURE
 356         bool
 357
 358 config MEMORY_FAILURE
 359         depends on MMU
 360         depends on ARCH_SUPPORTS_MEMORY_FAILURE
 361         bool "Enable recovery from hardware memory errors"
 362         select MEMORY_ISOLATION
 363         select RAS
 364         help
 365           Enables code to recover from some memory failures on systems
 366           with MCA recovery. This allows a system to continue running
 367           even when some of its memory has uncorrected errors. This requires
 368           special hardware support and typically ECC memory.
 369
 370 config HWPOISON_INJECT
 371         tristate "HWPoison pages injector"
 372         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 373         select PROC_PAGE_MONITOR
 374
 375 config NOMMU_INITIAL_TRIM_EXCESS
 376         int "Turn on mmap() excess space trimming before booting"
 377         depends on !MMU
 378         default 1
 379         help
 380           The NOMMU mmap() frequently needs to allocate large contiguous chunks
 381           of memory on which to store mappings, but it can only ask the system
 382           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 383           more than it requires.  To deal with this, mmap() is able to trim off
 384           the excess and return it to the allocator.
 385
 386           If trimming is enabled, the excess is trimmed off and returned to the
 387           system allocator, which can cause extra fragmentation, particularly
 388           if there are a lot of transient processes.
 389
 390           If trimming is disabled, the excess is kept, but not used, which for
 391           long-term mappings means that the space is wasted.
 392
 393           Trimming can be dynamically controlled through a sysctl option
 394           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 395           excess pages there must be before trimming should occur, or zero if
 396           no trimming is to occur.
 397
 398           This option specifies the initial value of this option.  The default
 399           of 1 says that all excess pages should be trimmed.
 400
 401           See Documentation/nommu-mmap.txt for more information.
 402
 403 config TRANSPARENT_HUGEPAGE
 404         bool "Transparent Hugepage Support"
 405         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 406         select COMPACTION
 407         help
 408           Transparent Hugepages allows the kernel to use huge pages and
 409           huge tlb transparently to the applications whenever possible.
 410           This feature can improve computing performance to certain
 411           applications by speeding up page faults during memory
 412           allocation, by reducing the number of tlb misses and by speeding
 413           up the pagetable walking.
 414
 415           If memory constrained on embedded, you may want to say N.
 416
 417 choice
 418         prompt "Transparent Hugepage Support sysfs defaults"
 419         depends on TRANSPARENT_HUGEPAGE
 420         default TRANSPARENT_HUGEPAGE_ALWAYS
 421         help
 422           Selects the sysfs defaults for Transparent Hugepage Support.
 423
 424         config TRANSPARENT_HUGEPAGE_ALWAYS
 425                 bool "always"
 426         help
 427           Enabling Transparent Hugepage always, can increase the
 428           memory footprint of applications without a guaranteed
 429           benefit but it will work automatically for all applications.
 430
 431         config TRANSPARENT_HUGEPAGE_MADVISE
 432                 bool "madvise"
 433         help
 434           Enabling Transparent Hugepage madvise, will only provide a
 435           performance improvement benefit to the applications using
 436           madvise(MADV_HUGEPAGE) but it won't risk to increase the
 437           memory footprint of applications without a guaranteed
 438           benefit.
 439 endchoice
 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 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 ZSMALLOC
 580         tristate "Memory allocator for compressed pages"
 581         depends on MMU
 582         default n
 583         help
 584           zsmalloc is a slab-based memory allocator designed to store
 585           compressed RAM pages.  zsmalloc uses virtual memory mapping
 586           in order to reduce fragmentation.  However, this results in a
 587           non-standard allocator interface where a handle, not a pointer, is
 588           returned by an alloc().  This handle must be mapped in order to
 589           access the allocated space.
 590
 591 config PGTABLE_MAPPING
 592         bool "Use page table mapping to access object in zsmalloc"
 593         depends on ZSMALLOC
 594         help
 595           By default, zsmalloc uses a copy-based object mapping method to
 596           access allocations that span two pages. However, if a particular
 597           architecture (ex, ARM) performs VM mapping faster than copying,
 598           then you should select this. This causes zsmalloc to use page table
 599           mapping rather than copying for object mapping.
 600
 601           You can check speed with zsmalloc benchmark:
 602           https://github.com/spartacus06/zsmapbench
 603
 604 config ZSMALLOC_STAT
 605         bool "Export zsmalloc statistics"
 606         depends on ZSMALLOC
 607         select DEBUG_FS
 608         help
 609           This option enables code in the zsmalloc to collect various
 610           statistics about whats happening in zsmalloc and exports that
 611           information to userspace via debugfs.
 612           If unsure, say N.
 613
 614 config GENERIC_EARLY_IOREMAP
 615         bool
 616
 617 config MAX_STACK_SIZE_MB
 618         int "Maximum user stack size for 32-bit processes (MB)"
 619         default 80
 620         range 8 256 if METAG
 621         range 8 2048
 622         depends on STACK_GROWSUP && (!64BIT || COMPAT)
 623         help
 624           This is the maximum stack size in Megabytes in the VM layout of 32-bit
 625           user processes when the stack grows upwards (currently only on parisc
 626           and metag arch). The stack will be located at the highest memory
 627           address minus the given value, unless the RLIMIT_STACK hard limit is
 628           changed to a smaller value in which case that is used.
 629
 630           A sane initial value is 80 MB.
 631
 632 # For architectures that support deferred memory initialisation
 633 config ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
 634         bool
 635
 636 config DEFERRED_STRUCT_PAGE_INIT
 637         bool "Defer initialisation of struct pages to kthreads"
 638         default n
 639         depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
 640         depends on MEMORY_HOTPLUG
 641         help
 642           Ordinarily all struct pages are initialised during early boot in a
 643           single thread. On very large machines this can take a considerable
 644           amount of time. If this option is set, large machines will bring up
 645           a subset of memmap at boot and then initialise the rest in parallel
 646           by starting one-off "pgdatinitX" kernel thread for each node X. This
 647           has a potential performance impact on processes running early in the
 648           lifetime of the system until these kthreads finish the
 649           initialisation.
 650
 651 config IDLE_PAGE_TRACKING
 652         bool "Enable idle page tracking"
 653         depends on SYSFS && MMU
 654         select PAGE_EXTENSION if !64BIT
 655         help
 656           This feature allows to estimate the amount of user pages that have
 657           not been touched during a given period of time. This information can
 658           be useful to tune memory cgroup limits and/or for job placement
 659           within a compute cluster.
 660
 661           See Documentation/vm/idle_page_tracking.txt for more details.
 662
 663 config ZONE_DEVICE
 664         bool "Device memory (pmem, etc...) hotplug support" if EXPERT
 665         depends on MEMORY_HOTPLUG
 666         depends on MEMORY_HOTREMOVE
 667         depends on SPARSEMEM_VMEMMAP
 668         depends on X86_64 #arch_add_memory() comprehends device memory
 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 FRAME_VECTOR
 680         bool
 681
 682 config ARCH_USES_HIGH_VMA_FLAGS
 683         bool
 684 config ARCH_HAS_PKEYS
 685         bool