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