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