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_HOTREMOVE
 196         bool "Allow for memory hot remove"
 197         select MEMORY_ISOLATION
 198         select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
 199         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 200         depends on MIGRATION
 201
 202 # Heavily threaded applications may benefit from splitting the mm-wide
 203 # page_table_lock, so that faults on different parts of the user address
 204 # space can be handled with less contention: split it at this NR_CPUS.
 205 # Default to 4 for wider testing, though 8 might be more appropriate.
 206 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 207 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 208 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 209 #
 210 config SPLIT_PTLOCK_CPUS
 211         int
 212         default "999999" if !MMU
 213         default "999999" if ARM && !CPU_CACHE_VIPT
 214         default "999999" if PARISC && !PA20
 215         default "4"
 216
 217 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
 218         bool
 219
 220 #
 221 # support for memory balloon
 222 config MEMORY_BALLOON
 223         bool
 224
 225 #
 226 # support for memory balloon compaction
 227 config BALLOON_COMPACTION
 228         bool "Allow for balloon memory compaction/migration"
 229         def_bool y
 230         depends on COMPACTION && MEMORY_BALLOON
 231         help
 232           Memory fragmentation introduced by ballooning might reduce
 233           significantly the number of 2MB contiguous memory blocks that can be
 234           used within a guest, thus imposing performance penalties associated
 235           with the reduced number of transparent huge pages that could be used
 236           by the guest workload. Allowing the compaction & migration for memory
 237           pages enlisted as being part of memory balloon devices avoids the
 238           scenario aforementioned and helps improving memory defragmentation.
 239
 240 #
 241 # support for memory compaction
 242 config COMPACTION
 243         bool "Allow for memory compaction"
 244         def_bool y
 245         select MIGRATION
 246         depends on MMU
 247         help
 248           Allows the compaction of memory for the allocation of huge pages.
 249
 250 #
 251 # support for page migration
 252 #
 253 config MIGRATION
 254         bool "Page migration"
 255         def_bool y
 256         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
 257         help
 258           Allows the migration of the physical location of pages of processes
 259           while the virtual addresses are not changed. This is useful in
 260           two situations. The first is on NUMA systems to put pages nearer
 261           to the processors accessing. The second is when allocating huge
 262           pages as migration can relocate pages to satisfy a huge page
 263           allocation instead of reclaiming.
 264
 265 config ARCH_ENABLE_HUGEPAGE_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 "2" if AVR32
 292         default "1"
 293
 294 config VIRT_TO_BUS
 295         bool
 296         help
 297           An architecture should select this if it implements the
 298           deprecated interface virt_to_bus().  All new architectures
 299           should probably not select this.
 300
 301
 302 config MMU_NOTIFIER
 303         bool
 304         select SRCU
 305
 306 config KSM
 307         bool "Enable KSM for page merging"
 308         depends on MMU
 309         help
 310           Enable Kernel Samepage Merging: KSM periodically scans those areas
 311           of an application's address space that an app has advised may be
 312           mergeable.  When it finds pages of identical content, it replaces
 313           the many instances by a single page with that content, so
 314           saving memory until one or another app needs to modify the content.
 315           Recommended for use with KVM, or with other duplicative applications.
 316           See Documentation/vm/ksm.txt for more information: KSM is inactive
 317           until a program has madvised that an area is MADV_MERGEABLE, and
 318           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 319
 320 config DEFAULT_MMAP_MIN_ADDR
 321         int "Low address space to protect from user allocation"
 322         depends on MMU
 323         default 4096
 324         help
 325           This is the portion of low virtual memory which should be protected
 326           from userspace allocation.  Keeping a user from writing to low pages
 327           can help reduce the impact of kernel NULL pointer bugs.
 328
 329           For most ia64, ppc64 and x86 users with lots of address space
 330           a value of 65536 is reasonable and should cause no problems.
 331           On arm and other archs it should not be higher than 32768.
 332           Programs which use vm86 functionality or have some need to map
 333           this low address space will need CAP_SYS_RAWIO or disable this
 334           protection by setting the value to 0.
 335
 336           This value can be changed after boot using the
 337           /proc/sys/vm/mmap_min_addr tunable.
 338
 339 config ARCH_SUPPORTS_MEMORY_FAILURE
 340         bool
 341
 342 config MEMORY_FAILURE
 343         depends on MMU
 344         depends on ARCH_SUPPORTS_MEMORY_FAILURE
 345         bool "Enable recovery from hardware memory errors"
 346         select MEMORY_ISOLATION
 347         select RAS
 348         help
 349           Enables code to recover from some memory failures on systems
 350           with MCA recovery. This allows a system to continue running
 351           even when some of its memory has uncorrected errors. This requires
 352           special hardware support and typically ECC memory.
 353
 354 config HWPOISON_INJECT
 355         tristate "HWPoison pages injector"
 356         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 357         select PROC_PAGE_MONITOR
 358
 359 config NOMMU_INITIAL_TRIM_EXCESS
 360         int "Turn on mmap() excess space trimming before booting"
 361         depends on !MMU
 362         default 1
 363         help
 364           The NOMMU mmap() frequently needs to allocate large contiguous chunks
 365           of memory on which to store mappings, but it can only ask the system
 366           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 367           more than it requires.  To deal with this, mmap() is able to trim off
 368           the excess and return it to the allocator.
 369
 370           If trimming is enabled, the excess is trimmed off and returned to the
 371           system allocator, which can cause extra fragmentation, particularly
 372           if there are a lot of transient processes.
 373
 374           If trimming is disabled, the excess is kept, but not used, which for
 375           long-term mappings means that the space is wasted.
 376
 377           Trimming can be dynamically controlled through a sysctl option
 378           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 379           excess pages there must be before trimming should occur, or zero if
 380           no trimming is to occur.
 381
 382           This option specifies the initial value of this option.  The default
 383           of 1 says that all excess pages should be trimmed.
 384
 385           See Documentation/nommu-mmap.txt for more information.
 386
 387 config TRANSPARENT_HUGEPAGE
 388         bool "Transparent Hugepage Support"
 389         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 390         select COMPACTION
 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 #
 426 # UP and nommu archs use km based percpu allocator
 427 #
 428 config NEED_PER_CPU_KM
 429         depends on !SMP
 430         bool
 431         default y
 432
 433 config CLEANCACHE
 434         bool "Enable cleancache driver to cache clean pages if tmem is present"
 435         default n
 436         help
 437           Cleancache can be thought of as a page-granularity victim cache
 438           for clean pages that the kernel's pageframe replacement algorithm
 439           (PFRA) would like to keep around, but can't since there isn't enough
 440           memory.  So when the PFRA "evicts" a page, it first attempts to use
 441           cleancache code to put the data contained in that page into
 442           "transcendent memory", memory that is not directly accessible or
 443           addressable by the kernel and is of unknown and possibly
 444           time-varying size.  And when a cleancache-enabled
 445           filesystem wishes to access a page in a file on disk, it first
 446           checks cleancache to see if it already contains it; if it does,
 447           the page is copied into the kernel and a disk access is avoided.
 448           When a transcendent memory driver is available (such as zcache or
 449           Xen transcendent memory), a significant I/O reduction
 450           may be achieved.  When none is available, all cleancache calls
 451           are reduced to a single pointer-compare-against-NULL resulting
 452           in a negligible performance hit.
 453
 454           If unsure, say Y to enable cleancache
 455
 456 config FRONTSWAP
 457         bool "Enable frontswap to cache swap pages if tmem is present"
 458         depends on SWAP
 459         default n
 460         help
 461           Frontswap is so named because it can be thought of as the opposite
 462           of a "backing" store for a swap device.  The data is stored into
 463           "transcendent memory", memory that is not directly accessible or
 464           addressable by the kernel and is of unknown and possibly
 465           time-varying size.  When space in transcendent memory is available,
 466           a significant swap I/O reduction may be achieved.  When none is
 467           available, all frontswap calls are reduced to a single pointer-
 468           compare-against-NULL resulting in a negligible performance hit
 469           and swap data is stored as normal on the matching swap device.
 470
 471           If unsure, say Y to enable frontswap.
 472
 473 config CMA
 474         bool "Contiguous Memory Allocator"
 475         depends on HAVE_MEMBLOCK && MMU
 476         select MIGRATION
 477         select MEMORY_ISOLATION
 478         help
 479           This enables the Contiguous Memory Allocator which allows other
 480           subsystems to allocate big physically-contiguous blocks of memory.
 481           CMA reserves a region of memory and allows only movable pages to
 482           be allocated from it. This way, the kernel can use the memory for
 483           pagecache and when a subsystem requests for contiguous area, the
 484           allocated pages are migrated away to serve the contiguous request.
 485
 486           If unsure, say "n".
 487
 488 config CMA_DEBUG
 489         bool "CMA debug messages (DEVELOPMENT)"
 490         depends on DEBUG_KERNEL && CMA
 491         help
 492           Turns on debug messages in CMA.  This produces KERN_DEBUG
 493           messages for every CMA call as well as various messages while
 494           processing calls such as dma_alloc_from_contiguous().
 495           This option does not affect warning and error messages.
 496
 497 config CMA_DEBUGFS
 498         bool "CMA debugfs interface"
 499         depends on CMA && DEBUG_FS
 500         help
 501           Turns on the DebugFS interface for CMA.
 502
 503 config CMA_AREAS
 504         int "Maximum count of the CMA areas"
 505         depends on CMA
 506         default 7
 507         help
 508           CMA allows to create CMA areas for particular purpose, mainly,
 509           used as device private area. This parameter sets the maximum
 510           number of CMA area in the system.
 511
 512           If unsure, leave the default value "7".
 513
 514 config MEM_SOFT_DIRTY
 515         bool "Track memory changes"
 516         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
 517         select PROC_PAGE_MONITOR
 518         help
 519           This option enables memory changes tracking by introducing a
 520           soft-dirty bit on pte-s. This bit it set when someone writes
 521           into a page just as regular dirty bit, but unlike the latter
 522           it can be cleared by hands.
 523
 524           See Documentation/vm/soft-dirty.txt for more details.
 525
 526 config ZSWAP
 527         bool "Compressed cache for swap pages (EXPERIMENTAL)"
 528         depends on FRONTSWAP && CRYPTO=y
 529         select CRYPTO_LZO
 530         select ZPOOL
 531         default n
 532         help
 533           A lightweight compressed cache for swap pages.  It takes
 534           pages that are in the process of being swapped out and attempts to
 535           compress them into a dynamically allocated RAM-based memory pool.
 536           This can result in a significant I/O reduction on swap device and,
 537           in the case where decompressing from RAM is faster that swap device
 538           reads, can also improve workload performance.
 539
 540           This is marked experimental because it is a new feature (as of
 541           v3.11) that interacts heavily with memory reclaim.  While these
 542           interactions don't cause any known issues on simple memory setups,
 543           they have not be fully explored on the large set of potential
 544           configurations and workloads that exist.
 545
 546 config ZPOOL
 547         tristate "Common API for compressed memory storage"
 548         default n
 549         help
 550           Compressed memory storage API.  This allows using either zbud or
 551           zsmalloc.
 552
 553 config ZBUD
 554         tristate "Low density storage for compressed pages"
 555         default n
 556         help
 557           A special purpose allocator for storing compressed pages.
 558           It is designed to store up to two compressed pages per physical
 559           page.  While this design limits storage density, it has simple and
 560           deterministic reclaim properties that make it preferable to a higher
 561           density approach when reclaim will be used.
 562
 563 config ZSMALLOC
 564         tristate "Memory allocator for compressed pages"
 565         depends on MMU
 566         default n
 567         help
 568           zsmalloc is a slab-based memory allocator designed to store
 569           compressed RAM pages.  zsmalloc uses virtual memory mapping
 570           in order to reduce fragmentation.  However, this results in a
 571           non-standard allocator interface where a handle, not a pointer, is
 572           returned by an alloc().  This handle must be mapped in order to
 573           access the allocated space.
 574
 575 config PGTABLE_MAPPING
 576         bool "Use page table mapping to access object in zsmalloc"
 577         depends on ZSMALLOC
 578         help
 579           By default, zsmalloc uses a copy-based object mapping method to
 580           access allocations that span two pages. However, if a particular
 581           architecture (ex, ARM) performs VM mapping faster than copying,
 582           then you should select this. This causes zsmalloc to use page table
 583           mapping rather than copying for object mapping.
 584
 585           You can check speed with zsmalloc benchmark:
 586           https://github.com/spartacus06/zsmapbench
 587
 588 config ZSMALLOC_STAT
 589         bool "Export zsmalloc statistics"
 590         depends on ZSMALLOC
 591         select DEBUG_FS
 592         help
 593           This option enables code in the zsmalloc to collect various
 594           statistics about whats happening in zsmalloc and exports that
 595           information to userspace via debugfs.
 596           If unsure, say N.
 597
 598 config GENERIC_EARLY_IOREMAP
 599         bool
 600
 601 config MAX_STACK_SIZE_MB
 602         int "Maximum user stack size for 32-bit processes (MB)"
 603         default 80
 604         range 8 256 if METAG
 605         range 8 2048
 606         depends on STACK_GROWSUP && (!64BIT || COMPAT)
 607         help
 608           This is the maximum stack size in Megabytes in the VM layout of 32-bit
 609           user processes when the stack grows upwards (currently only on parisc
 610           and metag arch). The stack will be located at the highest memory
 611           address minus the given value, unless the RLIMIT_STACK hard limit is
 612           changed to a smaller value in which case that is used.
 613
 614           A sane initial value is 80 MB.
 615
 616 # For architectures that support deferred memory initialisation
 617 config ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
 618         bool
 619
 620 config DEFERRED_STRUCT_PAGE_INIT
 621         bool "Defer initialisation of struct pages to kthreads"
 622         default n
 623         depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
 624         depends on MEMORY_HOTPLUG
 625         help
 626           Ordinarily all struct pages are initialised during early boot in a
 627           single thread. On very large machines this can take a considerable
 628           amount of time. If this option is set, large machines will bring up
 629           a subset of memmap at boot and then initialise the rest in parallel
 630           by starting one-off "pgdatinitX" kernel thread for each node X. This
 631           has a potential performance impact on processes running early in the
 632           lifetime of the system until these kthreads finish the
 633           initialisation.
 634
 635 config IDLE_PAGE_TRACKING
 636         bool "Enable idle page tracking"
 637         depends on SYSFS && MMU
 638         select PAGE_EXTENSION if !64BIT
 639         help
 640           This feature allows to estimate the amount of user pages that have
 641           not been touched during a given period of time. This information can
 642           be useful to tune memory cgroup limits and/or for job placement
 643           within a compute cluster.
 644
 645           See Documentation/vm/idle_page_tracking.txt for more details.
 646
 647 config ZONE_DEVICE
 648         bool "Device memory (pmem, etc...) hotplug support" if EXPERT
 649         depends on MEMORY_HOTPLUG
 650         depends on MEMORY_HOTREMOVE
 651         depends on SPARSEMEM_VMEMMAP
 652         depends on X86_64 #arch_add_memory() comprehends device memory
 653
 654         help
 655           Device memory hotplug support allows for establishing pmem,
 656           or other device driver discovered memory regions, in the
 657           memmap. This allows pfn_to_page() lookups of otherwise
 658           "device-physical" addresses which is needed for using a DAX
 659           mapping in an O_DIRECT operation, among other things.
 660
 661           If FS_DAX is enabled, then say Y.
 662
 663 config FRAME_VECTOR
 664         bool
 665
 666 config ARCH_USES_HIGH_VMA_FLAGS
 667         bool
 668 config ARCH_HAS_PKEYS
 669         bool