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         depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
 191
 192 config MEMORY_HOTPLUG_SPARSE
 193         def_bool y
 194         depends on SPARSEMEM && MEMORY_HOTPLUG
 195
 196 config MEMORY_HOTREMOVE
 197         bool "Allow for memory hot remove"
 198         select MEMORY_ISOLATION
 199         select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
 200         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 201         depends on MIGRATION
 202
 203 # Heavily threaded applications may benefit from splitting the mm-wide
 204 # page_table_lock, so that faults on different parts of the user address
 205 # space can be handled with less contention: split it at this NR_CPUS.
 206 # Default to 4 for wider testing, though 8 might be more appropriate.
 207 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 208 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 209 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 210 #
 211 config SPLIT_PTLOCK_CPUS
 212         int
 213         default "999999" if !MMU
 214         default "999999" if ARM && !CPU_CACHE_VIPT
 215         default "999999" if PARISC && !PA20
 216         default "4"
 217
 218 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
 219         bool
 220
 221 #
 222 # support for memory balloon
 223 config MEMORY_BALLOON
 224         bool
 225
 226 #
 227 # support for memory balloon compaction
 228 config BALLOON_COMPACTION
 229         bool "Allow for balloon memory compaction/migration"
 230         def_bool y
 231         depends on COMPACTION && MEMORY_BALLOON
 232         help
 233           Memory fragmentation introduced by ballooning might reduce
 234           significantly the number of 2MB contiguous memory blocks that can be
 235           used within a guest, thus imposing performance penalties associated
 236           with the reduced number of transparent huge pages that could be used
 237           by the guest workload. Allowing the compaction & migration for memory
 238           pages enlisted as being part of memory balloon devices avoids the
 239           scenario aforementioned and helps improving memory defragmentation.
 240
 241 #
 242 # support for memory compaction
 243 config COMPACTION
 244         bool "Allow for memory compaction"
 245         def_bool y
 246         select MIGRATION
 247         depends on MMU
 248         help
 249           Allows the compaction of memory for the allocation of huge pages.
 250
 251 #
 252 # support for page migration
 253 #
 254 config MIGRATION
 255         bool "Page migration"
 256         def_bool y
 257         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
 258         help
 259           Allows the migration of the physical location of pages of processes
 260           while the virtual addresses are not changed. This is useful in
 261           two situations. The first is on NUMA systems to put pages nearer
 262           to the processors accessing. The second is when allocating huge
 263           pages as migration can relocate pages to satisfy a huge page
 264           allocation instead of reclaiming.
 265
 266 config ARCH_ENABLE_HUGEPAGE_MIGRATION
 267         bool
 268
 269 config PHYS_ADDR_T_64BIT
 270         def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
 271
 272 config ZONE_DMA_FLAG
 273         int
 274         default "0" if !ZONE_DMA
 275         default "1"
 276
 277 config BOUNCE
 278         bool "Enable bounce buffers"
 279         default y
 280         depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 281         help
 282           Enable bounce buffers for devices that cannot access
 283           the full range of memory available to the CPU. Enabled
 284           by default when ZONE_DMA or HIGHMEM is selected, but you
 285           may say n to override this.
 286
 287 # On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
 288 # have more than 4GB of memory, but we don't currently use the IOTLB to present
 289 # a 32-bit address to OHCI.  So we need to use a bounce pool instead.
 290 config NEED_BOUNCE_POOL
 291         bool
 292         default y if TILE && USB_OHCI_HCD
 293
 294 config NR_QUICK
 295         int
 296         depends on QUICKLIST
 297         default "2" if AVR32
 298         default "1"
 299
 300 config VIRT_TO_BUS
 301         bool
 302         help
 303           An architecture should select this if it implements the
 304           deprecated interface virt_to_bus().  All new architectures
 305           should probably not select this.
 306
 307
 308 config MMU_NOTIFIER
 309         bool
 310         select SRCU
 311
 312 config KSM
 313         bool "Enable KSM for page merging"
 314         depends on MMU
 315         help
 316           Enable Kernel Samepage Merging: KSM periodically scans those areas
 317           of an application's address space that an app has advised may be
 318           mergeable.  When it finds pages of identical content, it replaces
 319           the many instances by a single page with that content, so
 320           saving memory until one or another app needs to modify the content.
 321           Recommended for use with KVM, or with other duplicative applications.
 322           See Documentation/vm/ksm.txt for more information: KSM is inactive
 323           until a program has madvised that an area is MADV_MERGEABLE, and
 324           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 325
 326 config DEFAULT_MMAP_MIN_ADDR
 327         int "Low address space to protect from user allocation"
 328         depends on MMU
 329         default 4096
 330         help
 331           This is the portion of low virtual memory which should be protected
 332           from userspace allocation.  Keeping a user from writing to low pages
 333           can help reduce the impact of kernel NULL pointer bugs.
 334
 335           For most ia64, ppc64 and x86 users with lots of address space
 336           a value of 65536 is reasonable and should cause no problems.
 337           On arm and other archs it should not be higher than 32768.
 338           Programs which use vm86 functionality or have some need to map
 339           this low address space will need CAP_SYS_RAWIO or disable this
 340           protection by setting the value to 0.
 341
 342           This value can be changed after boot using the
 343           /proc/sys/vm/mmap_min_addr tunable.
 344
 345 config ARCH_SUPPORTS_MEMORY_FAILURE
 346         bool
 347
 348 config MEMORY_FAILURE
 349         depends on MMU
 350         depends on ARCH_SUPPORTS_MEMORY_FAILURE
 351         bool "Enable recovery from hardware memory errors"
 352         select MEMORY_ISOLATION
 353         select RAS
 354         help
 355           Enables code to recover from some memory failures on systems
 356           with MCA recovery. This allows a system to continue running
 357           even when some of its memory has uncorrected errors. This requires
 358           special hardware support and typically ECC memory.
 359
 360 config HWPOISON_INJECT
 361         tristate "HWPoison pages injector"
 362         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 363         select PROC_PAGE_MONITOR
 364
 365 config NOMMU_INITIAL_TRIM_EXCESS
 366         int "Turn on mmap() excess space trimming before booting"
 367         depends on !MMU
 368         default 1
 369         help
 370           The NOMMU mmap() frequently needs to allocate large contiguous chunks
 371           of memory on which to store mappings, but it can only ask the system
 372           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 373           more than it requires.  To deal with this, mmap() is able to trim off
 374           the excess and return it to the allocator.
 375
 376           If trimming is enabled, the excess is trimmed off and returned to the
 377           system allocator, which can cause extra fragmentation, particularly
 378           if there are a lot of transient processes.
 379
 380           If trimming is disabled, the excess is kept, but not used, which for
 381           long-term mappings means that the space is wasted.
 382
 383           Trimming can be dynamically controlled through a sysctl option
 384           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 385           excess pages there must be before trimming should occur, or zero if
 386           no trimming is to occur.
 387
 388           This option specifies the initial value of this option.  The default
 389           of 1 says that all excess pages should be trimmed.
 390
 391           See Documentation/nommu-mmap.txt for more information.
 392
 393 config TRANSPARENT_HUGEPAGE
 394         bool "Transparent Hugepage Support"
 395         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 396         select COMPACTION
 397         help
 398           Transparent Hugepages allows the kernel to use huge pages and
 399           huge tlb transparently to the applications whenever possible.
 400           This feature can improve computing performance to certain
 401           applications by speeding up page faults during memory
 402           allocation, by reducing the number of tlb misses and by speeding
 403           up the pagetable walking.
 404
 405           If memory constrained on embedded, you may want to say N.
 406
 407 choice
 408         prompt "Transparent Hugepage Support sysfs defaults"
 409         depends on TRANSPARENT_HUGEPAGE
 410         default TRANSPARENT_HUGEPAGE_ALWAYS
 411         help
 412           Selects the sysfs defaults for Transparent Hugepage Support.
 413
 414         config TRANSPARENT_HUGEPAGE_ALWAYS
 415                 bool "always"
 416         help
 417           Enabling Transparent Hugepage always, can increase the
 418           memory footprint of applications without a guaranteed
 419           benefit but it will work automatically for all applications.
 420
 421         config TRANSPARENT_HUGEPAGE_MADVISE
 422                 bool "madvise"
 423         help
 424           Enabling Transparent Hugepage madvise, will only provide a
 425           performance improvement benefit to the applications using
 426           madvise(MADV_HUGEPAGE) but it won't risk to increase the
 427           memory footprint of applications without a guaranteed
 428           benefit.
 429 endchoice
 430
 431 #
 432 # UP and nommu archs use km based percpu allocator
 433 #
 434 config NEED_PER_CPU_KM
 435         depends on !SMP
 436         bool
 437         default y
 438
 439 config CLEANCACHE
 440         bool "Enable cleancache driver to cache clean pages if tmem is present"
 441         default n
 442         help
 443           Cleancache can be thought of as a page-granularity victim cache
 444           for clean pages that the kernel's pageframe replacement algorithm
 445           (PFRA) would like to keep around, but can't since there isn't enough
 446           memory.  So when the PFRA "evicts" a page, it first attempts to use
 447           cleancache code to put the data contained in that page into
 448           "transcendent memory", memory that is not directly accessible or
 449           addressable by the kernel and is of unknown and possibly
 450           time-varying size.  And when a cleancache-enabled
 451           filesystem wishes to access a page in a file on disk, it first
 452           checks cleancache to see if it already contains it; if it does,
 453           the page is copied into the kernel and a disk access is avoided.
 454           When a transcendent memory driver is available (such as zcache or
 455           Xen transcendent memory), a significant I/O reduction
 456           may be achieved.  When none is available, all cleancache calls
 457           are reduced to a single pointer-compare-against-NULL resulting
 458           in a negligible performance hit.
 459
 460           If unsure, say Y to enable cleancache
 461
 462 config FRONTSWAP
 463         bool "Enable frontswap to cache swap pages if tmem is present"
 464         depends on SWAP
 465         default n
 466         help
 467           Frontswap is so named because it can be thought of as the opposite
 468           of a "backing" store for a swap device.  The data is stored into
 469           "transcendent memory", memory that is not directly accessible or
 470           addressable by the kernel and is of unknown and possibly
 471           time-varying size.  When space in transcendent memory is available,
 472           a significant swap I/O reduction may be achieved.  When none is
 473           available, all frontswap calls are reduced to a single pointer-
 474           compare-against-NULL resulting in a negligible performance hit
 475           and swap data is stored as normal on the matching swap device.
 476
 477           If unsure, say Y to enable frontswap.
 478
 479 config CMA
 480         bool "Contiguous Memory Allocator"
 481         depends on HAVE_MEMBLOCK && MMU
 482         select MIGRATION
 483         select MEMORY_ISOLATION
 484         help
 485           This enables the Contiguous Memory Allocator which allows other
 486           subsystems to allocate big physically-contiguous blocks of memory.
 487           CMA reserves a region of memory and allows only movable pages to
 488           be allocated from it. This way, the kernel can use the memory for
 489           pagecache and when a subsystem requests for contiguous area, the
 490           allocated pages are migrated away to serve the contiguous request.
 491
 492           If unsure, say "n".
 493
 494 config CMA_DEBUG
 495         bool "CMA debug messages (DEVELOPMENT)"
 496         depends on DEBUG_KERNEL && CMA
 497         help
 498           Turns on debug messages in CMA.  This produces KERN_DEBUG
 499           messages for every CMA call as well as various messages while
 500           processing calls such as dma_alloc_from_contiguous().
 501           This option does not affect warning and error messages.
 502
 503 config CMA_DEBUGFS
 504         bool "CMA debugfs interface"
 505         depends on CMA && DEBUG_FS
 506         help
 507           Turns on the DebugFS interface for CMA.
 508
 509 config CMA_AREAS
 510         int "Maximum count of the CMA areas"
 511         depends on CMA
 512         default 7
 513         help
 514           CMA allows to create CMA areas for particular purpose, mainly,
 515           used as device private area. This parameter sets the maximum
 516           number of CMA area in the system.
 517
 518           If unsure, leave the default value "7".
 519
 520 config MEM_SOFT_DIRTY
 521         bool "Track memory changes"
 522         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
 523         select PROC_PAGE_MONITOR
 524         help
 525           This option enables memory changes tracking by introducing a
 526           soft-dirty bit on pte-s. This bit it set when someone writes
 527           into a page just as regular dirty bit, but unlike the latter
 528           it can be cleared by hands.
 529
 530           See Documentation/vm/soft-dirty.txt for more details.
 531
 532 config ZSWAP
 533         bool "Compressed cache for swap pages (EXPERIMENTAL)"
 534         depends on FRONTSWAP && CRYPTO=y
 535         select CRYPTO_LZO
 536         select ZPOOL
 537         default n
 538         help
 539           A lightweight compressed cache for swap pages.  It takes
 540           pages that are in the process of being swapped out and attempts to
 541           compress them into a dynamically allocated RAM-based memory pool.
 542           This can result in a significant I/O reduction on swap device and,
 543           in the case where decompressing from RAM is faster that swap device
 544           reads, can also improve workload performance.
 545
 546           This is marked experimental because it is a new feature (as of
 547           v3.11) that interacts heavily with memory reclaim.  While these
 548           interactions don't cause any known issues on simple memory setups,
 549           they have not be fully explored on the large set of potential
 550           configurations and workloads that exist.
 551
 552 config ZPOOL
 553         tristate "Common API for compressed memory storage"
 554         default n
 555         help
 556           Compressed memory storage API.  This allows using either zbud or
 557           zsmalloc.
 558
 559 config ZBUD
 560         tristate "Low density storage for compressed pages"
 561         default n
 562         help
 563           A special purpose allocator for storing compressed pages.
 564           It is designed to store up to two compressed pages per physical
 565           page.  While this design limits storage density, it has simple and
 566           deterministic reclaim properties that make it preferable to a higher
 567           density approach when reclaim will be used.
 568
 569 config ZSMALLOC
 570         tristate "Memory allocator for compressed pages"
 571         depends on MMU
 572         default n
 573         help
 574           zsmalloc is a slab-based memory allocator designed to store
 575           compressed RAM pages.  zsmalloc uses virtual memory mapping
 576           in order to reduce fragmentation.  However, this results in a
 577           non-standard allocator interface where a handle, not a pointer, is
 578           returned by an alloc().  This handle must be mapped in order to
 579           access the allocated space.
 580
 581 config PGTABLE_MAPPING
 582         bool "Use page table mapping to access object in zsmalloc"
 583         depends on ZSMALLOC
 584         help
 585           By default, zsmalloc uses a copy-based object mapping method to
 586           access allocations that span two pages. However, if a particular
 587           architecture (ex, ARM) performs VM mapping faster than copying,
 588           then you should select this. This causes zsmalloc to use page table
 589           mapping rather than copying for object mapping.
 590
 591           You can check speed with zsmalloc benchmark:
 592           https://github.com/spartacus06/zsmapbench
 593
 594 config ZSMALLOC_STAT
 595         bool "Export zsmalloc statistics"
 596         depends on ZSMALLOC
 597         select DEBUG_FS
 598         help
 599           This option enables code in the zsmalloc to collect various
 600           statistics about whats happening in zsmalloc and exports that
 601           information to userspace via debugfs.
 602           If unsure, say N.
 603
 604 config GENERIC_EARLY_IOREMAP
 605         bool
 606
 607 config MAX_STACK_SIZE_MB
 608         int "Maximum user stack size for 32-bit processes (MB)"
 609         default 80
 610         range 8 256 if METAG
 611         range 8 2048
 612         depends on STACK_GROWSUP && (!64BIT || COMPAT)
 613         help
 614           This is the maximum stack size in Megabytes in the VM layout of 32-bit
 615           user processes when the stack grows upwards (currently only on parisc
 616           and metag arch). The stack will be located at the highest memory
 617           address minus the given value, unless the RLIMIT_STACK hard limit is
 618           changed to a smaller value in which case that is used.
 619
 620           A sane initial value is 80 MB.
 621
 622 # For architectures that support deferred memory initialisation
 623 config ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
 624         bool
 625
 626 config DEFERRED_STRUCT_PAGE_INIT
 627         bool "Defer initialisation of struct pages to kswapd"
 628         default n
 629         depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
 630         depends on MEMORY_HOTPLUG
 631         help
 632           Ordinarily all struct pages are initialised during early boot in a
 633           single thread. On very large machines this can take a considerable
 634           amount of time. If this option is set, large machines will bring up
 635           a subset of memmap at boot and then initialise the rest in parallel
 636           when kswapd starts. This has a potential performance impact on
 637           processes running early in the lifetime of the systemm until kswapd
 638           finishes the initialisation.
 639
 640 config IDLE_PAGE_TRACKING
 641         bool "Enable idle page tracking"
 642         depends on SYSFS && MMU
 643         select PAGE_EXTENSION if !64BIT
 644         help
 645           This feature allows to estimate the amount of user pages that have
 646           not been touched during a given period of time. This information can
 647           be useful to tune memory cgroup limits and/or for job placement
 648           within a compute cluster.
 649
 650           See Documentation/vm/idle_page_tracking.txt for more details.
 651
 652 config ZONE_DEVICE
 653         bool "Device memory (pmem, etc...) hotplug support" if EXPERT
 654         default !ZONE_DMA
 655         depends on !ZONE_DMA
 656         depends on MEMORY_HOTPLUG
 657         depends on MEMORY_HOTREMOVE
 658         depends on X86_64 #arch_add_memory() comprehends device memory
 659
 660         help
 661           Device memory hotplug support allows for establishing pmem,
 662           or other device driver discovered memory regions, in the
 663           memmap. This allows pfn_to_page() lookups of otherwise
 664           "device-physical" addresses which is needed for using a DAX
 665           mapping in an O_DIRECT operation, among other things.
 666
 667           If FS_DAX is enabled, then say Y.
 668
 669 config FRAME_VECTOR
 670         bool