LXR linux/mm/Kconfig

   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_VMEMMAP
 119        bool "Sparse Memory virtual memmap"
 120        depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
 121        default y
 122        help
 123         SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
 124         pfn_to_page and page_to_pfn operations.  This is the most
 125         efficient option when sufficient kernel resources are available.
 126
 127# eventually, we can have this option just 'select SPARSEMEM'
 128config MEMORY_HOTPLUG
 129        bool "Allow for memory hot-add"
 130        depends on SPARSEMEM || X86_64_ACPI_NUMA
 131        depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG
 132        depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
 133
 134config MEMORY_HOTPLUG_SPARSE
 135        def_bool y
 136        depends on SPARSEMEM && MEMORY_HOTPLUG
 137
 138config MEMORY_HOTREMOVE
 139        bool "Allow for memory hot remove"
 140        depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 141        depends on MIGRATION
 142
 143#
 144# If we have space for more page flags then we can enable additional
 145# optimizations and functionality.
 146#
 147# Regular Sparsemem takes page flag bits for the sectionid if it does not
 148# use a virtual memmap. Disable extended page flags for 32 bit platforms
 149# that require the use of a sectionid in the page flags.
 150#
 151config PAGEFLAGS_EXTENDED
 152        def_bool y
 153        depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
 154
 155# Heavily threaded applications may benefit from splitting the mm-wide
 156# page_table_lock, so that faults on different parts of the user address
 157# space can be handled with less contention: split it at this NR_CPUS.
 158# Default to 4 for wider testing, though 8 might be more appropriate.
 159# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 160# PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 161#
 162config SPLIT_PTLOCK_CPUS
 163        int
 164        default "4096" if ARM && !CPU_CACHE_VIPT
 165        default "4096" if PARISC && !PA20
 166        default "4"
 167
 168#
 169# support for page migration
 170#
 171config MIGRATION
 172        bool "Page migration"
 173        def_bool y
 174        depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE
 175        help
 176          Allows the migration of the physical location of pages of processes
 177          while the virtual addresses are not changed. This is useful for
 178          example on NUMA systems to put pages nearer to the processors accessing
 179          the page.
 180
 181config PHYS_ADDR_T_64BIT
 182        def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
 183
 184config ZONE_DMA_FLAG
 185        int
 186        default "0" if !ZONE_DMA
 187        default "1"
 188
 189config BOUNCE
 190        def_bool y
 191        depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 192
 193config NR_QUICK
 194        int
 195        depends on QUICKLIST
 196        default "2" if SUPERH || AVR32
 197        default "1"
 198
 199config VIRT_TO_BUS
 200        def_bool y
 201        depends on !ARCH_NO_VIRT_TO_BUS
 202
 203config HAVE_MLOCK
 204        bool
 205        default y if MMU=y
 206
 207config HAVE_MLOCKED_PAGE_BIT
 208        bool
 209        default y if HAVE_MLOCK=y
 210
 211config MMU_NOTIFIER
 212        bool
 213
 214config KSM
 215        bool "Enable KSM for page merging"
 216        depends on MMU
 217        help
 218          Enable Kernel Samepage Merging: KSM periodically scans those areas
 219          of an application's address space that an app has advised may be
 220          mergeable.  When it finds pages of identical content, it replaces
 221          the many instances by a single resident page with that content, so
 222          saving memory until one or another app needs to modify the content.
 223          Recommended for use with KVM, or with other duplicative applications.
 224          See Documentation/vm/ksm.txt for more information: KSM is inactive
 225          until a program has madvised that an area is MADV_MERGEABLE, and
 226          root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 227
 228config DEFAULT_MMAP_MIN_ADDR
 229        int "Low address space to protect from user allocation"
 230        default 4096
 231        help
 232          This is the portion of low virtual memory which should be protected
 233          from userspace allocation.  Keeping a user from writing to low pages
 234          can help reduce the impact of kernel NULL pointer bugs.
 235
 236          For most ia64, ppc64 and x86 users with lots of address space
 237          a value of 65536 is reasonable and should cause no problems.
 238          On arm and other archs it should not be higher than 32768.
 239          Programs which use vm86 functionality or have some need to map
 240          this low address space will need CAP_SYS_RAWIO or disable this
 241          protection by setting the value to 0.
 242
 243          This value can be changed after boot using the
 244          /proc/sys/vm/mmap_min_addr tunable.
 245
 246config ARCH_SUPPORTS_MEMORY_FAILURE
 247        bool
 248
 249config MEMORY_FAILURE
 250        depends on MMU
 251        depends on ARCH_SUPPORTS_MEMORY_FAILURE
 252        bool "Enable recovery from hardware memory errors"
 253        help
 254          Enables code to recover from some memory failures on systems
 255          with MCA recovery. This allows a system to continue running
 256          even when some of its memory has uncorrected errors. This requires
 257          special hardware support and typically ECC memory.
 258
 259config HWPOISON_INJECT
 260        tristate "Poison pages injector"
 261        depends on MEMORY_FAILURE && DEBUG_KERNEL
 262
 263config NOMMU_INITIAL_TRIM_EXCESS
 264        int "Turn on mmap() excess space trimming before booting"
 265        depends on !MMU
 266        default 1
 267        help
 268          The NOMMU mmap() frequently needs to allocate large contiguous chunks
 269          of memory on which to store mappings, but it can only ask the system
 270          allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 271          more than it requires.  To deal with this, mmap() is able to trim off
 272          the excess and return it to the allocator.
 273
 274          If trimming is enabled, the excess is trimmed off and returned to the
 275          system allocator, which can cause extra fragmentation, particularly
 276          if there are a lot of transient processes.
 277
 278          If trimming is disabled, the excess is kept, but not used, which for
 279          long-term mappings means that the space is wasted.
 280
 281          Trimming can be dynamically controlled through a sysctl option
 282          (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 283          excess pages there must be before trimming should occur, or zero if
 284          no trimming is to occur.
 285
 286          This option specifies the initial value of this option.  The default
 287          of 1 says that all excess pages should be trimmed.
 288
 289          See Documentation/nommu-mmap.txt for more information.
 290