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