linux/mm/Kconfig
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   1config SELECT_MEMORY_MODEL
   2        def_bool y
   3        depends on ARCH_SELECT_MEMORY_MODEL
   4
   5choice
   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
  12config 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 an 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
  31config 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
  47config 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
  62endchoice
  63
  64config DISCONTIGMEM
  65        def_bool y
  66        depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
  67
  68config SPARSEMEM
  69        def_bool y
  70        depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
  71
  72config FLATMEM
  73        def_bool y
  74        depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
  75
  76config 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#
  85config NEED_MULTIPLE_NODES
  86        def_bool y
  87        depends on DISCONTIGMEM || NUMA
  88
  89config 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#
 103config 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#
 111config SPARSEMEM_EXTREME
 112        def_bool y
 113        depends on SPARSEMEM && !SPARSEMEM_STATIC
 114
 115config SPARSEMEM_VMEMMAP_ENABLE
 116        bool
 117
 118config SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
 119        def_bool y
 120        depends on SPARSEMEM && X86_64
 121
 122config 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
 131config HAVE_MEMBLOCK
 132        boolean
 133
 134config HAVE_MEMBLOCK_NODE_MAP
 135        boolean
 136
 137config ARCH_DISCARD_MEMBLOCK
 138        boolean
 139
 140config NO_BOOTMEM
 141        boolean
 142
 143config MEMORY_ISOLATION
 144        boolean
 145
 146config MOVABLE_NODE
 147        boolean "Enable to assign a node which has only movable memory"
 148        depends on HAVE_MEMBLOCK
 149        depends on NO_BOOTMEM
 150        depends on X86_64
 151        depends on NUMA
 152        default n
 153        help
 154          Allow a node to have only movable memory.  Pages used by the kernel,
 155          such as direct mapping pages cannot be migrated.  So the corresponding
 156          memory device cannot be hotplugged.  This option allows users to
 157          online all the memory of a node as movable memory so that the whole
 158          node can be hotplugged.  Users who don't use the memory hotplug
 159          feature are fine with this option on since they don't online memory
 160          as movable.
 161
 162          Say Y here if you want to hotplug a whole node.
 163          Say N here if you want kernel to use memory on all nodes evenly.
 164
 165#
 166# Only be set on architectures that have completely implemented memory hotplug
 167# feature. If you are not sure, don't touch it.
 168#
 169config HAVE_BOOTMEM_INFO_NODE
 170        def_bool n
 171
 172# eventually, we can have this option just 'select SPARSEMEM'
 173config MEMORY_HOTPLUG
 174        bool "Allow for memory hot-add"
 175        depends on SPARSEMEM || X86_64_ACPI_NUMA
 176        depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG
 177        depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
 178
 179config MEMORY_HOTPLUG_SPARSE
 180        def_bool y
 181        depends on SPARSEMEM && MEMORY_HOTPLUG
 182
 183config MEMORY_HOTREMOVE
 184        bool "Allow for memory hot remove"
 185        select MEMORY_ISOLATION
 186        select HAVE_BOOTMEM_INFO_NODE if X86_64
 187        depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 188        depends on MIGRATION
 189
 190#
 191# If we have space for more page flags then we can enable additional
 192# optimizations and functionality.
 193#
 194# Regular Sparsemem takes page flag bits for the sectionid if it does not
 195# use a virtual memmap. Disable extended page flags for 32 bit platforms
 196# that require the use of a sectionid in the page flags.
 197#
 198config PAGEFLAGS_EXTENDED
 199        def_bool y
 200        depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
 201
 202# Heavily threaded applications may benefit from splitting the mm-wide
 203# page_table_lock, so that faults on different parts of the user address
 204# space can be handled with less contention: split it at this NR_CPUS.
 205# Default to 4 for wider testing, though 8 might be more appropriate.
 206# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 207# PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 208# DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 209#
 210config SPLIT_PTLOCK_CPUS
 211        int
 212        default "999999" if ARM && !CPU_CACHE_VIPT
 213        default "999999" if PARISC && !PA20
 214        default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
 215        default "4"
 216
 217#
 218# support for memory balloon compaction
 219config BALLOON_COMPACTION
 220        bool "Allow for balloon memory compaction/migration"
 221        def_bool y
 222        depends on COMPACTION && VIRTIO_BALLOON
 223        help
 224          Memory fragmentation introduced by ballooning might reduce
 225          significantly the number of 2MB contiguous memory blocks that can be
 226          used within a guest, thus imposing performance penalties associated
 227          with the reduced number of transparent huge pages that could be used
 228          by the guest workload. Allowing the compaction & migration for memory
 229          pages enlisted as being part of memory balloon devices avoids the
 230          scenario aforementioned and helps improving memory defragmentation.
 231
 232#
 233# support for memory compaction
 234config COMPACTION
 235        bool "Allow for memory compaction"
 236        def_bool y
 237        select MIGRATION
 238        depends on MMU
 239        help
 240          Allows the compaction of memory for the allocation of huge pages.
 241
 242#
 243# support for page migration
 244#
 245config MIGRATION
 246        bool "Page migration"
 247        def_bool y
 248        depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA
 249        help
 250          Allows the migration of the physical location of pages of processes
 251          while the virtual addresses are not changed. This is useful in
 252          two situations. The first is on NUMA systems to put pages nearer
 253          to the processors accessing. The second is when allocating huge
 254          pages as migration can relocate pages to satisfy a huge page
 255          allocation instead of reclaiming.
 256
 257config PHYS_ADDR_T_64BIT
 258        def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
 259
 260config ZONE_DMA_FLAG
 261        int
 262        default "0" if !ZONE_DMA
 263        default "1"
 264
 265config BOUNCE
 266        def_bool y
 267        depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 268
 269# On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
 270# have more than 4GB of memory, but we don't currently use the IOTLB to present
 271# a 32-bit address to OHCI.  So we need to use a bounce pool instead.
 272#
 273# We also use the bounce pool to provide stable page writes for jbd.  jbd
 274# initiates buffer writeback without locking the page or setting PG_writeback,
 275# and fixing that behavior (a second time; jbd2 doesn't have this problem) is
 276# a major rework effort.  Instead, use the bounce buffer to snapshot pages
 277# (until jbd goes away).  The only jbd user is ext3.
 278config NEED_BOUNCE_POOL
 279        bool
 280        default y if (TILE && USB_OHCI_HCD) || (BLK_DEV_INTEGRITY && JBD)
 281
 282config NR_QUICK
 283        int
 284        depends on QUICKLIST
 285        default "2" if AVR32
 286        default "1"
 287
 288config VIRT_TO_BUS
 289        bool
 290        help
 291          An architecture should select this if it implements the
 292          deprecated interface virt_to_bus().  All new architectures
 293          should probably not select this.
 294
 295
 296config MMU_NOTIFIER
 297        bool
 298
 299config KSM
 300        bool "Enable KSM for page merging"
 301        depends on MMU
 302        help
 303          Enable Kernel Samepage Merging: KSM periodically scans those areas
 304          of an application's address space that an app has advised may be
 305          mergeable.  When it finds pages of identical content, it replaces
 306          the many instances by a single page with that content, so
 307          saving memory until one or another app needs to modify the content.
 308          Recommended for use with KVM, or with other duplicative applications.
 309          See Documentation/vm/ksm.txt for more information: KSM is inactive
 310          until a program has madvised that an area is MADV_MERGEABLE, and
 311          root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 312
 313config DEFAULT_MMAP_MIN_ADDR
 314        int "Low address space to protect from user allocation"
 315        depends on MMU
 316        default 4096
 317        help
 318          This is the portion of low virtual memory which should be protected
 319          from userspace allocation.  Keeping a user from writing to low pages
 320          can help reduce the impact of kernel NULL pointer bugs.
 321
 322          For most ia64, ppc64 and x86 users with lots of address space
 323          a value of 65536 is reasonable and should cause no problems.
 324          On arm and other archs it should not be higher than 32768.
 325          Programs which use vm86 functionality or have some need to map
 326          this low address space will need CAP_SYS_RAWIO or disable this
 327          protection by setting the value to 0.
 328
 329          This value can be changed after boot using the
 330          /proc/sys/vm/mmap_min_addr tunable.
 331
 332config ARCH_SUPPORTS_MEMORY_FAILURE
 333        bool
 334
 335config MEMORY_FAILURE
 336        depends on MMU
 337        depends on ARCH_SUPPORTS_MEMORY_FAILURE
 338        bool "Enable recovery from hardware memory errors"
 339        select MEMORY_ISOLATION
 340        help
 341          Enables code to recover from some memory failures on systems
 342          with MCA recovery. This allows a system to continue running
 343          even when some of its memory has uncorrected errors. This requires
 344          special hardware support and typically ECC memory.
 345
 346config HWPOISON_INJECT
 347        tristate "HWPoison pages injector"
 348        depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 349        select PROC_PAGE_MONITOR
 350
 351config NOMMU_INITIAL_TRIM_EXCESS
 352        int "Turn on mmap() excess space trimming before booting"
 353        depends on !MMU
 354        default 1
 355        help
 356          The NOMMU mmap() frequently needs to allocate large contiguous chunks
 357          of memory on which to store mappings, but it can only ask the system
 358          allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 359          more than it requires.  To deal with this, mmap() is able to trim off
 360          the excess and return it to the allocator.
 361
 362          If trimming is enabled, the excess is trimmed off and returned to the
 363          system allocator, which can cause extra fragmentation, particularly
 364          if there are a lot of transient processes.
 365
 366          If trimming is disabled, the excess is kept, but not used, which for
 367          long-term mappings means that the space is wasted.
 368
 369          Trimming can be dynamically controlled through a sysctl option
 370          (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 371          excess pages there must be before trimming should occur, or zero if
 372          no trimming is to occur.
 373
 374          This option specifies the initial value of this option.  The default
 375          of 1 says that all excess pages should be trimmed.
 376
 377          See Documentation/nommu-mmap.txt for more information.
 378
 379config TRANSPARENT_HUGEPAGE
 380        bool "Transparent Hugepage Support"
 381        depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 382        select COMPACTION
 383        help
 384          Transparent Hugepages allows the kernel to use huge pages and
 385          huge tlb transparently to the applications whenever possible.
 386          This feature can improve computing performance to certain
 387          applications by speeding up page faults during memory
 388          allocation, by reducing the number of tlb misses and by speeding
 389          up the pagetable walking.
 390
 391          If memory constrained on embedded, you may want to say N.
 392
 393choice
 394        prompt "Transparent Hugepage Support sysfs defaults"
 395        depends on TRANSPARENT_HUGEPAGE
 396        default TRANSPARENT_HUGEPAGE_ALWAYS
 397        help
 398          Selects the sysfs defaults for Transparent Hugepage Support.
 399
 400        config TRANSPARENT_HUGEPAGE_ALWAYS
 401                bool "always"
 402        help
 403          Enabling Transparent Hugepage always, can increase the
 404          memory footprint of applications without a guaranteed
 405          benefit but it will work automatically for all applications.
 406
 407        config TRANSPARENT_HUGEPAGE_MADVISE
 408                bool "madvise"
 409        help
 410          Enabling Transparent Hugepage madvise, will only provide a
 411          performance improvement benefit to the applications using
 412          madvise(MADV_HUGEPAGE) but it won't risk to increase the
 413          memory footprint of applications without a guaranteed
 414          benefit.
 415endchoice
 416
 417config CROSS_MEMORY_ATTACH
 418        bool "Cross Memory Support"
 419        depends on MMU
 420        default y
 421        help
 422          Enabling this option adds the system calls process_vm_readv and
 423          process_vm_writev which allow a process with the correct privileges
 424          to directly read from or write to to another process's address space.
 425          See the man page for more details.
 426
 427#
 428# UP and nommu archs use km based percpu allocator
 429#
 430config NEED_PER_CPU_KM
 431        depends on !SMP
 432        bool
 433        default y
 434
 435config CLEANCACHE
 436        bool "Enable cleancache driver to cache clean pages if tmem is present"
 437        default n
 438        help
 439          Cleancache can be thought of as a page-granularity victim cache
 440          for clean pages that the kernel's pageframe replacement algorithm
 441          (PFRA) would like to keep around, but can't since there isn't enough
 442          memory.  So when the PFRA "evicts" a page, it first attempts to use
 443          cleancache code to put the data contained in that page into
 444          "transcendent memory", memory that is not directly accessible or
 445          addressable by the kernel and is of unknown and possibly
 446          time-varying size.  And when a cleancache-enabled
 447          filesystem wishes to access a page in a file on disk, it first
 448          checks cleancache to see if it already contains it; if it does,
 449          the page is copied into the kernel and a disk access is avoided.
 450          When a transcendent memory driver is available (such as zcache or
 451          Xen transcendent memory), a significant I/O reduction
 452          may be achieved.  When none is available, all cleancache calls
 453          are reduced to a single pointer-compare-against-NULL resulting
 454          in a negligible performance hit.
 455
 456          If unsure, say Y to enable cleancache
 457
 458config FRONTSWAP
 459        bool "Enable frontswap to cache swap pages if tmem is present"
 460        depends on SWAP
 461        default n
 462        help
 463          Frontswap is so named because it can be thought of as the opposite
 464          of a "backing" store for a swap device.  The data is stored into
 465          "transcendent memory", memory that is not directly accessible or
 466          addressable by the kernel and is of unknown and possibly
 467          time-varying size.  When space in transcendent memory is available,
 468          a significant swap I/O reduction may be achieved.  When none is
 469          available, all frontswap calls are reduced to a single pointer-
 470          compare-against-NULL resulting in a negligible performance hit
 471          and swap data is stored as normal on the matching swap device.
 472
 473          If unsure, say Y to enable frontswap.
 474
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