mm/Kconfig

   1 # SPDX-License-Identifier: GPL-2.0-only
   2
   3 menu "Memory Management options"
   4
   5 config SELECT_MEMORY_MODEL
   6         def_bool y
   7         depends on ARCH_SELECT_MEMORY_MODEL
   8
   9 choice
  10         prompt "Memory model"
  11         depends on SELECT_MEMORY_MODEL
  12         default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
  13         default FLATMEM_MANUAL
  14         help
  15           This option allows you to change some of the ways that
  16           Linux manages its memory internally. Most users will
  17           only have one option here selected by the architecture
  18           configuration. This is normal.
  19
  20 config FLATMEM_MANUAL
  21         bool "Flat Memory"
  22         depends on !ARCH_SPARSEMEM_ENABLE || ARCH_FLATMEM_ENABLE
  23         help
  24           This option is best suited for non-NUMA systems with
  25           flat address space. The FLATMEM is the most efficient
  26           system in terms of performance and resource consumption
  27           and it is the best option for smaller systems.
  28
  29           For systems that have holes in their physical address
  30           spaces and for features like NUMA and memory hotplug,
  31           choose "Sparse Memory".
  32
  33           If unsure, choose this option (Flat Memory) over any other.
  34
  35 config SPARSEMEM_MANUAL
  36         bool "Sparse Memory"
  37         depends on ARCH_SPARSEMEM_ENABLE
  38         help
  39           This will be the only option for some systems, including
  40           memory hot-plug systems.  This is normal.
  41
  42           This option provides efficient support for systems with
  43           holes is their physical address space and allows memory
  44           hot-plug and hot-remove.
  45
  46           If unsure, choose "Flat Memory" over this option.
  47
  48 endchoice
  49
  50 config SPARSEMEM
  51         def_bool y
  52         depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
  53
  54 config FLATMEM
  55         def_bool y
  56         depends on !SPARSEMEM || FLATMEM_MANUAL
  57
  58 #
  59 # SPARSEMEM_EXTREME (which is the default) does some bootmem
  60 # allocations when sparse_init() is called.  If this cannot
  61 # be done on your architecture, select this option.  However,
  62 # statically allocating the mem_section[] array can potentially
  63 # consume vast quantities of .bss, so be careful.
  64 #
  65 # This option will also potentially produce smaller runtime code
  66 # with gcc 3.4 and later.
  67 #
  68 config SPARSEMEM_STATIC
  69         bool
  70
  71 #
  72 # Architecture platforms which require a two level mem_section in SPARSEMEM
  73 # must select this option. This is usually for architecture platforms with
  74 # an extremely sparse physical address space.
  75 #
  76 config SPARSEMEM_EXTREME
  77         def_bool y
  78         depends on SPARSEMEM && !SPARSEMEM_STATIC
  79
  80 config SPARSEMEM_VMEMMAP_ENABLE
  81         bool
  82
  83 config SPARSEMEM_VMEMMAP
  84         bool "Sparse Memory virtual memmap"
  85         depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
  86         default y
  87         help
  88           SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
  89           pfn_to_page and page_to_pfn operations.  This is the most
  90           efficient option when sufficient kernel resources are available.
  91
  92 config HAVE_MEMBLOCK_PHYS_MAP
  93         bool
  94
  95 config HAVE_FAST_GUP
  96         depends on MMU
  97         bool
  98
  99 config HOLES_IN_ZONE
 100         bool
 101
 102 # Don't discard allocated memory used to track "memory" and "reserved" memblocks
 103 # after early boot, so it can still be used to test for validity of memory.
 104 # Also, memblocks are updated with memory hot(un)plug.
 105 config ARCH_KEEP_MEMBLOCK
 106         bool
 107
 108 # Keep arch NUMA mapping infrastructure post-init.
 109 config NUMA_KEEP_MEMINFO
 110         bool
 111
 112 config MEMORY_ISOLATION
 113         bool
 114
 115 #
 116 # Only be set on architectures that have completely implemented memory hotplug
 117 # feature. If you are not sure, don't touch it.
 118 #
 119 config HAVE_BOOTMEM_INFO_NODE
 120         def_bool n
 121
 122 config ARCH_ENABLE_MEMORY_HOTPLUG
 123         bool
 124
 125 # eventually, we can have this option just 'select SPARSEMEM'
 126 config MEMORY_HOTPLUG
 127         bool "Allow for memory hot-add"
 128         select MEMORY_ISOLATION
 129         depends on SPARSEMEM || X86_64_ACPI_NUMA
 130         depends on ARCH_ENABLE_MEMORY_HOTPLUG
 131         depends on 64BIT || BROKEN
 132         select NUMA_KEEP_MEMINFO if NUMA
 133
 134 config MEMORY_HOTPLUG_SPARSE
 135         def_bool y
 136         depends on SPARSEMEM && MEMORY_HOTPLUG
 137
 138 config MEMORY_HOTPLUG_DEFAULT_ONLINE
 139         bool "Online the newly added memory blocks by default"
 140         depends on MEMORY_HOTPLUG
 141         help
 142           This option sets the default policy setting for memory hotplug
 143           onlining policy (/sys/devices/system/memory/auto_online_blocks) which
 144           determines what happens to newly added memory regions. Policy setting
 145           can always be changed at runtime.
 146           See Documentation/admin-guide/mm/memory-hotplug.rst for more information.
 147
 148           Say Y here if you want all hot-plugged memory blocks to appear in
 149           'online' state by default.
 150           Say N here if you want the default policy to keep all hot-plugged
 151           memory blocks in 'offline' state.
 152
 153 config ARCH_ENABLE_MEMORY_HOTREMOVE
 154         bool
 155
 156 config MEMORY_HOTREMOVE
 157         bool "Allow for memory hot remove"
 158         select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
 159         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 160         depends on MIGRATION
 161
 162 config MHP_MEMMAP_ON_MEMORY
 163         def_bool y
 164         depends on MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP
 165         depends on ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
 166
 167 # Heavily threaded applications may benefit from splitting the mm-wide
 168 # page_table_lock, so that faults on different parts of the user address
 169 # space can be handled with less contention: split it at this NR_CPUS.
 170 # Default to 4 for wider testing, though 8 might be more appropriate.
 171 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 172 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 173 # SPARC32 allocates multiple pte tables within a single page, and therefore
 174 # a per-page lock leads to problems when multiple tables need to be locked
 175 # at the same time (e.g. copy_page_range()).
 176 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 177 #
 178 config SPLIT_PTLOCK_CPUS
 179         int
 180         default "999999" if !MMU
 181         default "999999" if ARM && !CPU_CACHE_VIPT
 182         default "999999" if PARISC && !PA20
 183         default "999999" if SPARC32
 184         default "4"
 185
 186 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
 187         bool
 188
 189 #
 190 # support for memory balloon
 191 config MEMORY_BALLOON
 192         bool
 193
 194 #
 195 # support for memory balloon compaction
 196 config BALLOON_COMPACTION
 197         bool "Allow for balloon memory compaction/migration"
 198         def_bool y
 199         depends on COMPACTION && MEMORY_BALLOON
 200         help
 201           Memory fragmentation introduced by ballooning might reduce
 202           significantly the number of 2MB contiguous memory blocks that can be
 203           used within a guest, thus imposing performance penalties associated
 204           with the reduced number of transparent huge pages that could be used
 205           by the guest workload. Allowing the compaction & migration for memory
 206           pages enlisted as being part of memory balloon devices avoids the
 207           scenario aforementioned and helps improving memory defragmentation.
 208
 209 #
 210 # support for memory compaction
 211 config COMPACTION
 212         bool "Allow for memory compaction"
 213         def_bool y
 214         select MIGRATION
 215         depends on MMU
 216         help
 217           Compaction is the only memory management component to form
 218           high order (larger physically contiguous) memory blocks
 219           reliably. The page allocator relies on compaction heavily and
 220           the lack of the feature can lead to unexpected OOM killer
 221           invocations for high order memory requests. You shouldn't
 222           disable this option unless there really is a strong reason for
 223           it and then we would be really interested to hear about that at
 224           linux-mm@kvack.org.
 225
 226 #
 227 # support for free page reporting
 228 config PAGE_REPORTING
 229         bool "Free page reporting"
 230         def_bool n
 231         help
 232           Free page reporting allows for the incremental acquisition of
 233           free pages from the buddy allocator for the purpose of reporting
 234           those pages to another entity, such as a hypervisor, so that the
 235           memory can be freed within the host for other uses.
 236
 237 #
 238 # support for page migration
 239 #
 240 config MIGRATION
 241         bool "Page migration"
 242         def_bool y
 243         depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
 244         help
 245           Allows the migration of the physical location of pages of processes
 246           while the virtual addresses are not changed. This is useful in
 247           two situations. The first is on NUMA systems to put pages nearer
 248           to the processors accessing. The second is when allocating huge
 249           pages as migration can relocate pages to satisfy a huge page
 250           allocation instead of reclaiming.
 251
 252 config ARCH_ENABLE_HUGEPAGE_MIGRATION
 253         bool
 254
 255 config ARCH_ENABLE_THP_MIGRATION
 256         bool
 257
 258 config HUGETLB_PAGE_SIZE_VARIABLE
 259         def_bool n
 260         help
 261           Allows the pageblock_order value to be dynamic instead of just standard
 262           HUGETLB_PAGE_ORDER when there are multiple HugeTLB page sizes available
 263           on a platform.
 264
 265 config CONTIG_ALLOC
 266         def_bool (MEMORY_ISOLATION && COMPACTION) || CMA
 267
 268 config PHYS_ADDR_T_64BIT
 269         def_bool 64BIT
 270
 271 config BOUNCE
 272         bool "Enable bounce buffers"
 273         default y
 274         depends on BLOCK && MMU && HIGHMEM
 275         help
 276           Enable bounce buffers for devices that cannot access the full range of
 277           memory available to the CPU. Enabled by default when HIGHMEM is
 278           selected, but you may say n to override this.
 279
 280 config VIRT_TO_BUS
 281         bool
 282         help
 283           An architecture should select this if it implements the
 284           deprecated interface virt_to_bus().  All new architectures
 285           should probably not select this.
 286
 287
 288 config MMU_NOTIFIER
 289         bool
 290         select SRCU
 291         select INTERVAL_TREE
 292
 293 config KSM
 294         bool "Enable KSM for page merging"
 295         depends on MMU
 296         select XXHASH
 297         help
 298           Enable Kernel Samepage Merging: KSM periodically scans those areas
 299           of an application's address space that an app has advised may be
 300           mergeable.  When it finds pages of identical content, it replaces
 301           the many instances by a single page with that content, so
 302           saving memory until one or another app needs to modify the content.
 303           Recommended for use with KVM, or with other duplicative applications.
 304           See Documentation/vm/ksm.rst for more information: KSM is inactive
 305           until a program has madvised that an area is MADV_MERGEABLE, and
 306           root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 307
 308 config DEFAULT_MMAP_MIN_ADDR
 309         int "Low address space to protect from user allocation"
 310         depends on MMU
 311         default 4096
 312         help
 313           This is the portion of low virtual memory which should be protected
 314           from userspace allocation.  Keeping a user from writing to low pages
 315           can help reduce the impact of kernel NULL pointer bugs.
 316
 317           For most ia64, ppc64 and x86 users with lots of address space
 318           a value of 65536 is reasonable and should cause no problems.
 319           On arm and other archs it should not be higher than 32768.
 320           Programs which use vm86 functionality or have some need to map
 321           this low address space will need CAP_SYS_RAWIO or disable this
 322           protection by setting the value to 0.
 323
 324           This value can be changed after boot using the
 325           /proc/sys/vm/mmap_min_addr tunable.
 326
 327 config ARCH_SUPPORTS_MEMORY_FAILURE
 328         bool
 329
 330 config MEMORY_FAILURE
 331         depends on MMU
 332         depends on ARCH_SUPPORTS_MEMORY_FAILURE
 333         bool "Enable recovery from hardware memory errors"
 334         select MEMORY_ISOLATION
 335         select RAS
 336         help
 337           Enables code to recover from some memory failures on systems
 338           with MCA recovery. This allows a system to continue running
 339           even when some of its memory has uncorrected errors. This requires
 340           special hardware support and typically ECC memory.
 341
 342 config HWPOISON_INJECT
 343         tristate "HWPoison pages injector"
 344         depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 345         select PROC_PAGE_MONITOR
 346
 347 config NOMMU_INITIAL_TRIM_EXCESS
 348         int "Turn on mmap() excess space trimming before booting"
 349         depends on !MMU
 350         default 1
 351         help
 352           The NOMMU mmap() frequently needs to allocate large contiguous chunks
 353           of memory on which to store mappings, but it can only ask the system
 354           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 355           more than it requires.  To deal with this, mmap() is able to trim off
 356           the excess and return it to the allocator.
 357
 358           If trimming is enabled, the excess is trimmed off and returned to the
 359           system allocator, which can cause extra fragmentation, particularly
 360           if there are a lot of transient processes.
 361
 362           If trimming is disabled, the excess is kept, but not used, which for
 363           long-term mappings means that the space is wasted.
 364
 365           Trimming can be dynamically controlled through a sysctl option
 366           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 367           excess pages there must be before trimming should occur, or zero if
 368           no trimming is to occur.
 369
 370           This option specifies the initial value of this option.  The default
 371           of 1 says that all excess pages should be trimmed.
 372
 373           See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
 374
 375 config TRANSPARENT_HUGEPAGE
 376         bool "Transparent Hugepage Support"
 377         depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 378         select COMPACTION
 379         select XARRAY_MULTI
 380         help
 381           Transparent Hugepages allows the kernel to use huge pages and
 382           huge tlb transparently to the applications whenever possible.
 383           This feature can improve computing performance to certain
 384           applications by speeding up page faults during memory
 385           allocation, by reducing the number of tlb misses and by speeding
 386           up the pagetable walking.
 387
 388           If memory constrained on embedded, you may want to say N.
 389
 390 choice
 391         prompt "Transparent Hugepage Support sysfs defaults"
 392         depends on TRANSPARENT_HUGEPAGE
 393         default TRANSPARENT_HUGEPAGE_ALWAYS
 394         help
 395           Selects the sysfs defaults for Transparent Hugepage Support.
 396
 397         config TRANSPARENT_HUGEPAGE_ALWAYS
 398                 bool "always"
 399         help
 400           Enabling Transparent Hugepage always, can increase the
 401           memory footprint of applications without a guaranteed
 402           benefit but it will work automatically for all applications.
 403
 404         config TRANSPARENT_HUGEPAGE_MADVISE
 405                 bool "madvise"
 406         help
 407           Enabling Transparent Hugepage madvise, will only provide a
 408           performance improvement benefit to the applications using
 409           madvise(MADV_HUGEPAGE) but it won't risk to increase the
 410           memory footprint of applications without a guaranteed
 411           benefit.
 412 endchoice
 413
 414 config ARCH_WANTS_THP_SWAP
 415         def_bool n
 416
 417 config THP_SWAP
 418         def_bool y
 419         depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP
 420         help
 421           Swap transparent huge pages in one piece, without splitting.
 422           XXX: For now, swap cluster backing transparent huge page
 423           will be split after swapout.
 424
 425           For selection by architectures with reasonable THP sizes.
 426
 427 #
 428 # UP and nommu archs use km based percpu allocator
 429 #
 430 config NEED_PER_CPU_KM
 431         depends on !SMP
 432         bool
 433         default y
 434
 435 config CLEANCACHE
 436         bool "Enable cleancache driver to cache clean pages if tmem is present"
 437         help
 438           Cleancache can be thought of as a page-granularity victim cache
 439           for clean pages that the kernel's pageframe replacement algorithm
 440           (PFRA) would like to keep around, but can't since there isn't enough
 441           memory.  So when the PFRA "evicts" a page, it first attempts to use
 442           cleancache code to put the data contained in that page into
 443           "transcendent memory", memory that is not directly accessible or
 444           addressable by the kernel and is of unknown and possibly
 445           time-varying size.  And when a cleancache-enabled
 446           filesystem wishes to access a page in a file on disk, it first
 447           checks cleancache to see if it already contains it; if it does,
 448           the page is copied into the kernel and a disk access is avoided.
 449           When a transcendent memory driver is available (such as zcache or
 450           Xen transcendent memory), a significant I/O reduction
 451           may be achieved.  When none is available, all cleancache calls
 452           are reduced to a single pointer-compare-against-NULL resulting
 453           in a negligible performance hit.
 454
 455           If unsure, say Y to enable cleancache
 456
 457 config FRONTSWAP
 458         bool "Enable frontswap to cache swap pages if tmem is present"
 459         depends on SWAP
 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 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_SYSFS
 504         bool "CMA information through sysfs interface"
 505         depends on CMA && SYSFS
 506         help
 507           This option exposes some sysfs attributes to get information
 508           from CMA.
 509
 510 config CMA_AREAS
 511         int "Maximum count of the CMA areas"
 512         depends on CMA
 513         default 19 if NUMA
 514         default 7
 515         help
 516           CMA allows to create CMA areas for particular purpose, mainly,
 517           used as device private area. This parameter sets the maximum
 518           number of CMA area in the system.
 519
 520           If unsure, leave the default value "7" in UMA and "19" in NUMA.
 521
 522 config MEM_SOFT_DIRTY
 523         bool "Track memory changes"
 524         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
 525         select PROC_PAGE_MONITOR
 526         help
 527           This option enables memory changes tracking by introducing a
 528           soft-dirty bit on pte-s. This bit it set when someone writes
 529           into a page just as regular dirty bit, but unlike the latter
 530           it can be cleared by hands.
 531
 532           See Documentation/admin-guide/mm/soft-dirty.rst for more details.
 533
 534 config ZSWAP
 535         bool "Compressed cache for swap pages (EXPERIMENTAL)"
 536         depends on FRONTSWAP && CRYPTO=y
 537         select ZPOOL
 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 choice
 553         prompt "Compressed cache for swap pages default compressor"
 554         depends on ZSWAP
 555         default ZSWAP_COMPRESSOR_DEFAULT_LZO
 556         help
 557           Selects the default compression algorithm for the compressed cache
 558           for swap pages.
 559
 560           For an overview what kind of performance can be expected from
 561           a particular compression algorithm please refer to the benchmarks
 562           available at the following LWN page:
 563           https://lwn.net/Articles/751795/
 564
 565           If in doubt, select 'LZO'.
 566
 567           The selection made here can be overridden by using the kernel
 568           command line 'zswap.compressor=' option.
 569
 570 config ZSWAP_COMPRESSOR_DEFAULT_DEFLATE
 571         bool "Deflate"
 572         select CRYPTO_DEFLATE
 573         help
 574           Use the Deflate algorithm as the default compression algorithm.
 575
 576 config ZSWAP_COMPRESSOR_DEFAULT_LZO
 577         bool "LZO"
 578         select CRYPTO_LZO
 579         help
 580           Use the LZO algorithm as the default compression algorithm.
 581
 582 config ZSWAP_COMPRESSOR_DEFAULT_842
 583         bool "842"
 584         select CRYPTO_842
 585         help
 586           Use the 842 algorithm as the default compression algorithm.
 587
 588 config ZSWAP_COMPRESSOR_DEFAULT_LZ4
 589         bool "LZ4"
 590         select CRYPTO_LZ4
 591         help
 592           Use the LZ4 algorithm as the default compression algorithm.
 593
 594 config ZSWAP_COMPRESSOR_DEFAULT_LZ4HC
 595         bool "LZ4HC"
 596         select CRYPTO_LZ4HC
 597         help
 598           Use the LZ4HC algorithm as the default compression algorithm.
 599
 600 config ZSWAP_COMPRESSOR_DEFAULT_ZSTD
 601         bool "zstd"
 602         select CRYPTO_ZSTD
 603         help
 604           Use the zstd algorithm as the default compression algorithm.
 605 endchoice
 606
 607 config ZSWAP_COMPRESSOR_DEFAULT
 608        string
 609        depends on ZSWAP
 610        default "deflate" if ZSWAP_COMPRESSOR_DEFAULT_DEFLATE
 611        default "lzo" if ZSWAP_COMPRESSOR_DEFAULT_LZO
 612        default "842" if ZSWAP_COMPRESSOR_DEFAULT_842
 613        default "lz4" if ZSWAP_COMPRESSOR_DEFAULT_LZ4
 614        default "lz4hc" if ZSWAP_COMPRESSOR_DEFAULT_LZ4HC
 615        default "zstd" if ZSWAP_COMPRESSOR_DEFAULT_ZSTD
 616        default ""
 617
 618 choice
 619         prompt "Compressed cache for swap pages default allocator"
 620         depends on ZSWAP
 621         default ZSWAP_ZPOOL_DEFAULT_ZBUD
 622         help
 623           Selects the default allocator for the compressed cache for
 624           swap pages.
 625           The default is 'zbud' for compatibility, however please do
 626           read the description of each of the allocators below before
 627           making a right choice.
 628
 629           The selection made here can be overridden by using the kernel
 630           command line 'zswap.zpool=' option.
 631
 632 config ZSWAP_ZPOOL_DEFAULT_ZBUD
 633         bool "zbud"
 634         select ZBUD
 635         help
 636           Use the zbud allocator as the default allocator.
 637
 638 config ZSWAP_ZPOOL_DEFAULT_Z3FOLD
 639         bool "z3fold"
 640         select Z3FOLD
 641         help
 642           Use the z3fold allocator as the default allocator.
 643
 644 config ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
 645         bool "zsmalloc"
 646         select ZSMALLOC
 647         help
 648           Use the zsmalloc allocator as the default allocator.
 649 endchoice
 650
 651 config ZSWAP_ZPOOL_DEFAULT
 652        string
 653        depends on ZSWAP
 654        default "zbud" if ZSWAP_ZPOOL_DEFAULT_ZBUD
 655        default "z3fold" if ZSWAP_ZPOOL_DEFAULT_Z3FOLD
 656        default "zsmalloc" if ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
 657        default ""
 658
 659 config ZSWAP_DEFAULT_ON
 660         bool "Enable the compressed cache for swap pages by default"
 661         depends on ZSWAP
 662         help
 663           If selected, the compressed cache for swap pages will be enabled
 664           at boot, otherwise it will be disabled.
 665
 666           The selection made here can be overridden by using the kernel
 667           command line 'zswap.enabled=' option.
 668
 669 config ZPOOL
 670         tristate "Common API for compressed memory storage"
 671         help
 672           Compressed memory storage API.  This allows using either zbud or
 673           zsmalloc.
 674
 675 config ZBUD
 676         tristate "Low (Up to 2x) density storage for compressed pages"
 677         depends on ZPOOL
 678         help
 679           A special purpose allocator for storing compressed pages.
 680           It is designed to store up to two compressed pages per physical
 681           page.  While this design limits storage density, it has simple and
 682           deterministic reclaim properties that make it preferable to a higher
 683           density approach when reclaim will be used.
 684
 685 config Z3FOLD
 686         tristate "Up to 3x density storage for compressed pages"
 687         depends on ZPOOL
 688         help
 689           A special purpose allocator for storing compressed pages.
 690           It is designed to store up to three compressed pages per physical
 691           page. It is a ZBUD derivative so the simplicity and determinism are
 692           still there.
 693
 694 config ZSMALLOC
 695         tristate "Memory allocator for compressed pages"
 696         depends on MMU
 697         help
 698           zsmalloc is a slab-based memory allocator designed to store
 699           compressed RAM pages.  zsmalloc uses virtual memory mapping
 700           in order to reduce fragmentation.  However, this results in a
 701           non-standard allocator interface where a handle, not a pointer, is
 702           returned by an alloc().  This handle must be mapped in order to
 703           access the allocated space.
 704
 705 config ZSMALLOC_STAT
 706         bool "Export zsmalloc statistics"
 707         depends on ZSMALLOC
 708         select DEBUG_FS
 709         help
 710           This option enables code in the zsmalloc to collect various
 711           statistics about what's happening in zsmalloc and exports that
 712           information to userspace via debugfs.
 713           If unsure, say N.
 714
 715 config GENERIC_EARLY_IOREMAP
 716         bool
 717
 718 config STACK_MAX_DEFAULT_SIZE_MB
 719         int "Default maximum user stack size for 32-bit processes (MB)"
 720         default 100
 721         range 8 2048
 722         depends on STACK_GROWSUP && (!64BIT || COMPAT)
 723         help
 724           This is the maximum stack size in Megabytes in the VM layout of 32-bit
 725           user processes when the stack grows upwards (currently only on parisc
 726           arch) when the RLIMIT_STACK hard limit is unlimited.
 727
 728           A sane initial value is 100 MB.
 729
 730 config DEFERRED_STRUCT_PAGE_INIT
 731         bool "Defer initialisation of struct pages to kthreads"
 732         depends on SPARSEMEM
 733         depends on !NEED_PER_CPU_KM
 734         depends on 64BIT
 735         select PADATA
 736         help
 737           Ordinarily all struct pages are initialised during early boot in a
 738           single thread. On very large machines this can take a considerable
 739           amount of time. If this option is set, large machines will bring up
 740           a subset of memmap at boot and then initialise the rest in parallel.
 741           This has a potential performance impact on tasks running early in the
 742           lifetime of the system until these kthreads finish the
 743           initialisation.
 744
 745 config IDLE_PAGE_TRACKING
 746         bool "Enable idle page tracking"
 747         depends on SYSFS && MMU
 748         select PAGE_EXTENSION if !64BIT
 749         help
 750           This feature allows to estimate the amount of user pages that have
 751           not been touched during a given period of time. This information can
 752           be useful to tune memory cgroup limits and/or for job placement
 753           within a compute cluster.
 754
 755           See Documentation/admin-guide/mm/idle_page_tracking.rst for
 756           more details.
 757
 758 config ARCH_HAS_CACHE_LINE_SIZE
 759         bool
 760
 761 config ARCH_HAS_PTE_DEVMAP
 762         bool
 763
 764 config ARCH_HAS_ZONE_DMA_SET
 765         bool
 766
 767 config ZONE_DMA
 768         bool "Support DMA zone" if ARCH_HAS_ZONE_DMA_SET
 769         default y if ARM64 || X86
 770
 771 config ZONE_DMA32
 772         bool "Support DMA32 zone" if ARCH_HAS_ZONE_DMA_SET
 773         depends on !X86_32
 774         default y if ARM64
 775
 776 config ZONE_DEVICE
 777         bool "Device memory (pmem, HMM, etc...) hotplug support"
 778         depends on MEMORY_HOTPLUG
 779         depends on MEMORY_HOTREMOVE
 780         depends on SPARSEMEM_VMEMMAP
 781         depends on ARCH_HAS_PTE_DEVMAP
 782         select XARRAY_MULTI
 783
 784         help
 785           Device memory hotplug support allows for establishing pmem,
 786           or other device driver discovered memory regions, in the
 787           memmap. This allows pfn_to_page() lookups of otherwise
 788           "device-physical" addresses which is needed for using a DAX
 789           mapping in an O_DIRECT operation, among other things.
 790
 791           If FS_DAX is enabled, then say Y.
 792
 793 config DEV_PAGEMAP_OPS
 794         bool
 795
 796 #
 797 # Helpers to mirror range of the CPU page tables of a process into device page
 798 # tables.
 799 #
 800 config HMM_MIRROR
 801         bool
 802         depends on MMU
 803
 804 config DEVICE_PRIVATE
 805         bool "Unaddressable device memory (GPU memory, ...)"
 806         depends on ZONE_DEVICE
 807         select DEV_PAGEMAP_OPS
 808
 809         help
 810           Allows creation of struct pages to represent unaddressable device
 811           memory; i.e., memory that is only accessible from the device (or
 812           group of devices). You likely also want to select HMM_MIRROR.
 813
 814 config VMAP_PFN
 815         bool
 816
 817 config ARCH_USES_HIGH_VMA_FLAGS
 818         bool
 819 config ARCH_HAS_PKEYS
 820         bool
 821
 822 config PERCPU_STATS
 823         bool "Collect percpu memory statistics"
 824         help
 825           This feature collects and exposes statistics via debugfs. The
 826           information includes global and per chunk statistics, which can
 827           be used to help understand percpu memory usage.
 828
 829 config GUP_TEST
 830         bool "Enable infrastructure for get_user_pages()-related unit tests"
 831         depends on DEBUG_FS
 832         help
 833           Provides /sys/kernel/debug/gup_test, which in turn provides a way
 834           to make ioctl calls that can launch kernel-based unit tests for
 835           the get_user_pages*() and pin_user_pages*() family of API calls.
 836
 837           These tests include benchmark testing of the _fast variants of
 838           get_user_pages*() and pin_user_pages*(), as well as smoke tests of
 839           the non-_fast variants.
 840
 841           There is also a sub-test that allows running dump_page() on any
 842           of up to eight pages (selected by command line args) within the
 843           range of user-space addresses. These pages are either pinned via
 844           pin_user_pages*(), or pinned via get_user_pages*(), as specified
 845           by other command line arguments.
 846
 847           See tools/testing/selftests/vm/gup_test.c
 848
 849 comment "GUP_TEST needs to have DEBUG_FS enabled"
 850         depends on !GUP_TEST && !DEBUG_FS
 851
 852 config GUP_GET_PTE_LOW_HIGH
 853         bool
 854
 855 config READ_ONLY_THP_FOR_FS
 856         bool "Read-only THP for filesystems (EXPERIMENTAL)"
 857         depends on TRANSPARENT_HUGEPAGE && SHMEM
 858
 859         help
 860           Allow khugepaged to put read-only file-backed pages in THP.
 861
 862           This is marked experimental because it is a new feature. Write
 863           support of file THPs will be developed in the next few release
 864           cycles.
 865
 866 config ARCH_HAS_PTE_SPECIAL
 867         bool
 868
 869 #
 870 # Some architectures require a special hugepage directory format that is
 871 # required to support multiple hugepage sizes. For example a4fe3ce76
 872 # "powerpc/mm: Allow more flexible layouts for hugepage pagetables"
 873 # introduced it on powerpc.  This allows for a more flexible hugepage
 874 # pagetable layouts.
 875 #
 876 config ARCH_HAS_HUGEPD
 877         bool
 878
 879 config MAPPING_DIRTY_HELPERS
 880         bool
 881
 882 config KMAP_LOCAL
 883         bool
 884
 885 # struct io_mapping based helper.  Selected by drivers that need them
 886 config IO_MAPPING
 887         bool
 888
 889 config SECRETMEM
 890         def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
 891
 892 endmenu