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
 146# eventually, we can have this option just 'select SPARSEMEM'
 147config MEMORY_HOTPLUG
 148        bool "Allow for memory hot-add"
 149        select MEMORY_ISOLATION
 150        depends on SPARSEMEM || X86_64_ACPI_NUMA
 151        depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG
 152        depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
 153
 154config MEMORY_HOTPLUG_SPARSE
 155        def_bool y
 156        depends on SPARSEMEM && MEMORY_HOTPLUG
 157
 158config MEMORY_HOTREMOVE
 159        bool "Allow for memory hot remove"
 160        depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 161        depends on MIGRATION
 162
 163#
 164# If we have space for more page flags then we can enable additional
 165# optimizations and functionality.
 166#
 167# Regular Sparsemem takes page flag bits for the sectionid if it does not
 168# use a virtual memmap. Disable extended page flags for 32 bit platforms
 169# that require the use of a sectionid in the page flags.
 170#
 171config PAGEFLAGS_EXTENDED
 172        def_bool y
 173        depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
 174
 175# Heavily threaded applications may benefit from splitting the mm-wide
 176# page_table_lock, so that faults on different parts of the user address
 177# space can be handled with less contention: split it at this NR_CPUS.
 178# Default to 4 for wider testing, though 8 might be more appropriate.
 179# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 180# PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 181# DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 182#
 183config SPLIT_PTLOCK_CPUS
 184        int
 185        default "999999" if ARM && !CPU_CACHE_VIPT
 186        default "999999" if PARISC && !PA20
 187        default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
 188        default "4"
 189
 190#
 191# support for memory compaction
 192config COMPACTION
 193        bool "Allow for memory compaction"
 194        select MIGRATION
 195        depends on MMU
 196        help
 197          Allows the compaction of memory for the allocation of huge pages.
 198
 199#
 200# support for page migration
 201#
 202config MIGRATION
 203        bool "Page migration"
 204        def_bool y
 205        depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA
 206        help
 207          Allows the migration of the physical location of pages of processes
 208          while the virtual addresses are not changed. This is useful in
 209          two situations. The first is on NUMA systems to put pages nearer
 210          to the processors accessing. The second is when allocating huge
 211          pages as migration can relocate pages to satisfy a huge page
 212          allocation instead of reclaiming.
 213
 214config PHYS_ADDR_T_64BIT
 215        def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
 216
 217config ZONE_DMA_FLAG
 218        int
 219        default "0" if !ZONE_DMA
 220        default "1"
 221
 222config BOUNCE
 223        def_bool y
 224        depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 225
 226config NR_QUICK
 227        int
 228        depends on QUICKLIST
 229        default "2" if AVR32
 230        default "1"
 231
 232config VIRT_TO_BUS
 233        def_bool y
 234        depends on !ARCH_NO_VIRT_TO_BUS
 235
 236config MMU_NOTIFIER
 237        bool
 238
 239config KSM
 240        bool "Enable KSM for page merging"
 241        depends on MMU
 242        help
 243          Enable Kernel Samepage Merging: KSM periodically scans those areas
 244          of an application's address space that an app has advised may be
 245          mergeable.  When it finds pages of identical content, it replaces
 246          the many instances by a single page with that content, so
 247          saving memory until one or another app needs to modify the content.
 248          Recommended for use with KVM, or with other duplicative applications.
 249          See Documentation/vm/ksm.txt for more information: KSM is inactive
 250          until a program has madvised that an area is MADV_MERGEABLE, and
 251          root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 252
 253config DEFAULT_MMAP_MIN_ADDR
 254        int "Low address space to protect from user allocation"
 255        depends on MMU
 256        default 4096
 257        help
 258          This is the portion of low virtual memory which should be protected
 259          from userspace allocation.  Keeping a user from writing to low pages
 260          can help reduce the impact of kernel NULL pointer bugs.
 261
 262          For most ia64, ppc64 and x86 users with lots of address space
 263          a value of 65536 is reasonable and should cause no problems.
 264          On arm and other archs it should not be higher than 32768.
 265          Programs which use vm86 functionality or have some need to map
 266          this low address space will need CAP_SYS_RAWIO or disable this
 267          protection by setting the value to 0.
 268
 269          This value can be changed after boot using the
 270          /proc/sys/vm/mmap_min_addr tunable.
 271
 272config ARCH_SUPPORTS_MEMORY_FAILURE
 273        bool
 274
 275config MEMORY_FAILURE
 276        depends on MMU
 277        depends on ARCH_SUPPORTS_MEMORY_FAILURE
 278        bool "Enable recovery from hardware memory errors"
 279        select MEMORY_ISOLATION
 280        help
 281          Enables code to recover from some memory failures on systems
 282          with MCA recovery. This allows a system to continue running
 283          even when some of its memory has uncorrected errors. This requires
 284          special hardware support and typically ECC memory.
 285
 286config HWPOISON_INJECT
 287        tristate "HWPoison pages injector"
 288        depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 289        select PROC_PAGE_MONITOR
 290
 291config NOMMU_INITIAL_TRIM_EXCESS
 292        int "Turn on mmap() excess space trimming before booting"
 293        depends on !MMU
 294        default 1
 295        help
 296          The NOMMU mmap() frequently needs to allocate large contiguous chunks
 297          of memory on which to store mappings, but it can only ask the system
 298          allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 299          more than it requires.  To deal with this, mmap() is able to trim off
 300          the excess and return it to the allocator.
 301
 302          If trimming is enabled, the excess is trimmed off and returned to the
 303          system allocator, which can cause extra fragmentation, particularly
 304          if there are a lot of transient processes.
 305
 306          If trimming is disabled, the excess is kept, but not used, which for
 307          long-term mappings means that the space is wasted.
 308
 309          Trimming can be dynamically controlled through a sysctl option
 310          (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 311          excess pages there must be before trimming should occur, or zero if
 312          no trimming is to occur.
 313
 314          This option specifies the initial value of this option.  The default
 315          of 1 says that all excess pages should be trimmed.
 316
 317          See Documentation/nommu-mmap.txt for more information.
 318
 319config TRANSPARENT_HUGEPAGE
 320        bool "Transparent Hugepage Support"
 321        depends on X86 && MMU
 322        select COMPACTION
 323        help
 324          Transparent Hugepages allows the kernel to use huge pages and
 325          huge tlb transparently to the applications whenever possible.
 326          This feature can improve computing performance to certain
 327          applications by speeding up page faults during memory
 328          allocation, by reducing the number of tlb misses and by speeding
 329          up the pagetable walking.
 330
 331          If memory constrained on embedded, you may want to say N.
 332
 333choice
 334        prompt "Transparent Hugepage Support sysfs defaults"
 335        depends on TRANSPARENT_HUGEPAGE
 336        default TRANSPARENT_HUGEPAGE_ALWAYS
 337        help
 338          Selects the sysfs defaults for Transparent Hugepage Support.
 339
 340        config TRANSPARENT_HUGEPAGE_ALWAYS
 341                bool "always"
 342        help
 343          Enabling Transparent Hugepage always, can increase the
 344          memory footprint of applications without a guaranteed
 345          benefit but it will work automatically for all applications.
 346
 347        config TRANSPARENT_HUGEPAGE_MADVISE
 348                bool "madvise"
 349        help
 350          Enabling Transparent Hugepage madvise, will only provide a
 351          performance improvement benefit to the applications using
 352          madvise(MADV_HUGEPAGE) but it won't risk to increase the
 353          memory footprint of applications without a guaranteed
 354          benefit.
 355endchoice
 356
 357config CROSS_MEMORY_ATTACH
 358        bool "Cross Memory Support"
 359        depends on MMU
 360        default y
 361        help
 362          Enabling this option adds the system calls process_vm_readv and
 363          process_vm_writev which allow a process with the correct privileges
 364          to directly read from or write to to another process's address space.
 365          See the man page for more details.
 366
 367#
 368# UP and nommu archs use km based percpu allocator
 369#
 370config NEED_PER_CPU_KM
 371        depends on !SMP
 372        bool
 373        default y
 374
 375config CLEANCACHE
 376        bool "Enable cleancache driver to cache clean pages if tmem is present"
 377        default n
 378        help
 379          Cleancache can be thought of as a page-granularity victim cache
 380          for clean pages that the kernel's pageframe replacement algorithm
 381          (PFRA) would like to keep around, but can't since there isn't enough
 382          memory.  So when the PFRA "evicts" a page, it first attempts to use
 383          cleancache code to put the data contained in that page into
 384          "transcendent memory", memory that is not directly accessible or
 385          addressable by the kernel and is of unknown and possibly
 386          time-varying size.  And when a cleancache-enabled
 387          filesystem wishes to access a page in a file on disk, it first
 388          checks cleancache to see if it already contains it; if it does,
 389          the page is copied into the kernel and a disk access is avoided.
 390          When a transcendent memory driver is available (such as zcache or
 391          Xen transcendent memory), a significant I/O reduction
 392          may be achieved.  When none is available, all cleancache calls
 393          are reduced to a single pointer-compare-against-NULL resulting
 394          in a negligible performance hit.
 395
 396          If unsure, say Y to enable cleancache
 397
 398config FRONTSWAP
 399        bool "Enable frontswap to cache swap pages if tmem is present"
 400        depends on SWAP
 401        default n
 402        help
 403          Frontswap is so named because it can be thought of as the opposite
 404          of a "backing" store for a swap device.  The data is stored into
 405          "transcendent memory", memory that is not directly accessible or
 406          addressable by the kernel and is of unknown and possibly
 407          time-varying size.  When space in transcendent memory is available,
 408          a significant swap I/O reduction may be achieved.  When none is
 409          available, all frontswap calls are reduced to a single pointer-
 410          compare-against-NULL resulting in a negligible performance hit
 411          and swap data is stored as normal on the matching swap device.
 412
 413          If unsure, say Y to enable frontswap.
 414
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