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
 134# eventually, we can have this option just 'select SPARSEMEM'
 135config MEMORY_HOTPLUG
 136        bool "Allow for memory hot-add"
 137        depends on SPARSEMEM || X86_64_ACPI_NUMA
 138        depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG
 139        depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
 140
 141config MEMORY_HOTPLUG_SPARSE
 142        def_bool y
 143        depends on SPARSEMEM && MEMORY_HOTPLUG
 144
 145config MEMORY_HOTREMOVE
 146        bool "Allow for memory hot remove"
 147        depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 148        depends on MIGRATION
 149
 150#
 151# If we have space for more page flags then we can enable additional
 152# optimizations and functionality.
 153#
 154# Regular Sparsemem takes page flag bits for the sectionid if it does not
 155# use a virtual memmap. Disable extended page flags for 32 bit platforms
 156# that require the use of a sectionid in the page flags.
 157#
 158config PAGEFLAGS_EXTENDED
 159        def_bool y
 160        depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
 161
 162# Heavily threaded applications may benefit from splitting the mm-wide
 163# page_table_lock, so that faults on different parts of the user address
 164# space can be handled with less contention: split it at this NR_CPUS.
 165# Default to 4 for wider testing, though 8 might be more appropriate.
 166# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 167# PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 168# DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 169#
 170config SPLIT_PTLOCK_CPUS
 171        int
 172        default "999999" if ARM && !CPU_CACHE_VIPT
 173        default "999999" if PARISC && !PA20
 174        default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
 175        default "4"
 176
 177#
 178# support for memory compaction
 179config COMPACTION
 180        bool "Allow for memory compaction"
 181        select MIGRATION
 182        depends on MMU
 183        help
 184          Allows the compaction of memory for the allocation of huge pages.
 185
 186#
 187# support for page migration
 188#
 189config MIGRATION
 190        bool "Page migration"
 191        def_bool y
 192        depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION
 193        help
 194          Allows the migration of the physical location of pages of processes
 195          while the virtual addresses are not changed. This is useful in
 196          two situations. The first is on NUMA systems to put pages nearer
 197          to the processors accessing. The second is when allocating huge
 198          pages as migration can relocate pages to satisfy a huge page
 199          allocation instead of reclaiming.
 200
 201config PHYS_ADDR_T_64BIT
 202        def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
 203
 204config ZONE_DMA_FLAG
 205        int
 206        default "0" if !ZONE_DMA
 207        default "1"
 208
 209config BOUNCE
 210        def_bool y
 211        depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 212
 213config NR_QUICK
 214        int
 215        depends on QUICKLIST
 216        default "2" if AVR32
 217        default "1"
 218
 219config VIRT_TO_BUS
 220        def_bool y
 221        depends on !ARCH_NO_VIRT_TO_BUS
 222
 223config MMU_NOTIFIER
 224        bool
 225
 226config KSM
 227        bool "Enable KSM for page merging"
 228        depends on MMU
 229        help
 230          Enable Kernel Samepage Merging: KSM periodically scans those areas
 231          of an application's address space that an app has advised may be
 232          mergeable.  When it finds pages of identical content, it replaces
 233          the many instances by a single page with that content, so
 234          saving memory until one or another app needs to modify the content.
 235          Recommended for use with KVM, or with other duplicative applications.
 236          See Documentation/vm/ksm.txt for more information: KSM is inactive
 237          until a program has madvised that an area is MADV_MERGEABLE, and
 238          root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 239
 240config DEFAULT_MMAP_MIN_ADDR
 241        int "Low address space to protect from user allocation"
 242        depends on MMU
 243        default 4096
 244        help
 245          This is the portion of low virtual memory which should be protected
 246          from userspace allocation.  Keeping a user from writing to low pages
 247          can help reduce the impact of kernel NULL pointer bugs.
 248
 249          For most ia64, ppc64 and x86 users with lots of address space
 250          a value of 65536 is reasonable and should cause no problems.
 251          On arm and other archs it should not be higher than 32768.
 252          Programs which use vm86 functionality or have some need to map
 253          this low address space will need CAP_SYS_RAWIO or disable this
 254          protection by setting the value to 0.
 255
 256          This value can be changed after boot using the
 257          /proc/sys/vm/mmap_min_addr tunable.
 258
 259config ARCH_SUPPORTS_MEMORY_FAILURE
 260        bool
 261
 262config MEMORY_FAILURE
 263        depends on MMU
 264        depends on ARCH_SUPPORTS_MEMORY_FAILURE
 265        bool "Enable recovery from hardware memory errors"
 266        help
 267          Enables code to recover from some memory failures on systems
 268          with MCA recovery. This allows a system to continue running
 269          even when some of its memory has uncorrected errors. This requires
 270          special hardware support and typically ECC memory.
 271
 272config HWPOISON_INJECT
 273        tristate "HWPoison pages injector"
 274        depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 275        select PROC_PAGE_MONITOR
 276
 277config NOMMU_INITIAL_TRIM_EXCESS
 278        int "Turn on mmap() excess space trimming before booting"
 279        depends on !MMU
 280        default 1
 281        help
 282          The NOMMU mmap() frequently needs to allocate large contiguous chunks
 283          of memory on which to store mappings, but it can only ask the system
 284          allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 285          more than it requires.  To deal with this, mmap() is able to trim off
 286          the excess and return it to the allocator.
 287
 288          If trimming is enabled, the excess is trimmed off and returned to the
 289          system allocator, which can cause extra fragmentation, particularly
 290          if there are a lot of transient processes.
 291
 292          If trimming is disabled, the excess is kept, but not used, which for
 293          long-term mappings means that the space is wasted.
 294
 295          Trimming can be dynamically controlled through a sysctl option
 296          (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 297          excess pages there must be before trimming should occur, or zero if
 298          no trimming is to occur.
 299
 300          This option specifies the initial value of this option.  The default
 301          of 1 says that all excess pages should be trimmed.
 302
 303          See Documentation/nommu-mmap.txt for more information.
 304
 305config TRANSPARENT_HUGEPAGE
 306        bool "Transparent Hugepage Support"
 307        depends on X86 && MMU
 308        select COMPACTION
 309        help
 310          Transparent Hugepages allows the kernel to use huge pages and
 311          huge tlb transparently to the applications whenever possible.
 312          This feature can improve computing performance to certain
 313          applications by speeding up page faults during memory
 314          allocation, by reducing the number of tlb misses and by speeding
 315          up the pagetable walking.
 316
 317          If memory constrained on embedded, you may want to say N.
 318
 319choice
 320        prompt "Transparent Hugepage Support sysfs defaults"
 321        depends on TRANSPARENT_HUGEPAGE
 322        default TRANSPARENT_HUGEPAGE_ALWAYS
 323        help
 324          Selects the sysfs defaults for Transparent Hugepage Support.
 325
 326        config TRANSPARENT_HUGEPAGE_ALWAYS
 327                bool "always"
 328        help
 329          Enabling Transparent Hugepage always, can increase the
 330          memory footprint of applications without a guaranteed
 331          benefit but it will work automatically for all applications.
 332
 333        config TRANSPARENT_HUGEPAGE_MADVISE
 334                bool "madvise"
 335        help
 336          Enabling Transparent Hugepage madvise, will only provide a
 337          performance improvement benefit to the applications using
 338          madvise(MADV_HUGEPAGE) but it won't risk to increase the
 339          memory footprint of applications without a guaranteed
 340          benefit.
 341endchoice
 342
 343#
 344# UP and nommu archs use km based percpu allocator
 345#
 346config NEED_PER_CPU_KM
 347        depends on !SMP
 348        bool
 349        default y
 350
 351config CLEANCACHE
 352        bool "Enable cleancache driver to cache clean pages if tmem is present"
 353        default n
 354        help
 355          Cleancache can be thought of as a page-granularity victim cache
 356          for clean pages that the kernel's pageframe replacement algorithm
 357          (PFRA) would like to keep around, but can't since there isn't enough
 358          memory.  So when the PFRA "evicts" a page, it first attempts to use
 359          cleancache code to put the data contained in that page into
 360          "transcendent memory", memory that is not directly accessible or
 361          addressable by the kernel and is of unknown and possibly
 362          time-varying size.  And when a cleancache-enabled
 363          filesystem wishes to access a page in a file on disk, it first
 364          checks cleancache to see if it already contains it; if it does,
 365          the page is copied into the kernel and a disk access is avoided.
 366          When a transcendent memory driver is available (such as zcache or
 367          Xen transcendent memory), a significant I/O reduction
 368          may be achieved.  When none is available, all cleancache calls
 369          are reduced to a single pointer-compare-against-NULL resulting
 370          in a negligible performance hit.
 371
 372          If unsure, say Y to enable cleancache
 373
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