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