linux/mm/Kconfig
<<
>>
Prefs
   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
 143# eventually, we can have this option just 'select SPARSEMEM'
 144config MEMORY_HOTPLUG
 145        bool "Allow for memory hot-add"
 146        depends on SPARSEMEM || X86_64_ACPI_NUMA
 147        depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG
 148        depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
 149
 150config MEMORY_HOTPLUG_SPARSE
 151        def_bool y
 152        depends on SPARSEMEM && MEMORY_HOTPLUG
 153
 154config MEMORY_HOTREMOVE
 155        bool "Allow for memory hot remove"
 156        depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 157        depends on MIGRATION
 158
 159#
 160# If we have space for more page flags then we can enable additional
 161# optimizations and functionality.
 162#
 163# Regular Sparsemem takes page flag bits for the sectionid if it does not
 164# use a virtual memmap. Disable extended page flags for 32 bit platforms
 165# that require the use of a sectionid in the page flags.
 166#
 167config PAGEFLAGS_EXTENDED
 168        def_bool y
 169        depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
 170
 171# Heavily threaded applications may benefit from splitting the mm-wide
 172# page_table_lock, so that faults on different parts of the user address
 173# space can be handled with less contention: split it at this NR_CPUS.
 174# Default to 4 for wider testing, though 8 might be more appropriate.
 175# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 176# PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 177# DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 178#
 179config SPLIT_PTLOCK_CPUS
 180        int
 181        default "999999" if ARM && !CPU_CACHE_VIPT
 182        default "999999" if PARISC && !PA20
 183        default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
 184        default "4"
 185
 186#
 187# support for memory compaction
 188config COMPACTION
 189        bool "Allow for memory compaction"
 190        select MIGRATION
 191        depends on MMU
 192        help
 193          Allows the compaction of memory for the allocation of huge pages.
 194
 195#
 196# support for page migration
 197#
 198config MIGRATION
 199        bool "Page migration"
 200        def_bool y
 201        depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA
 202        help
 203          Allows the migration of the physical location of pages of processes
 204          while the virtual addresses are not changed. This is useful in
 205          two situations. The first is on NUMA systems to put pages nearer
 206          to the processors accessing. The second is when allocating huge
 207          pages as migration can relocate pages to satisfy a huge page
 208          allocation instead of reclaiming.
 209
 210config PHYS_ADDR_T_64BIT
 211        def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
 212
 213config ZONE_DMA_FLAG
 214        int
 215        default "0" if !ZONE_DMA
 216        default "1"
 217
 218config BOUNCE
 219        def_bool y
 220        depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 221
 222config NR_QUICK
 223        int
 224        depends on QUICKLIST
 225        default "2" if AVR32
 226        default "1"
 227
 228config VIRT_TO_BUS
 229        def_bool y
 230        depends on !ARCH_NO_VIRT_TO_BUS
 231
 232config MMU_NOTIFIER
 233        bool
 234
 235config KSM
 236        bool "Enable KSM for page merging"
 237        depends on MMU
 238        help
 239          Enable Kernel Samepage Merging: KSM periodically scans those areas
 240          of an application's address space that an app has advised may be
 241          mergeable.  When it finds pages of identical content, it replaces
 242          the many instances by a single page with that content, so
 243          saving memory until one or another app needs to modify the content.
 244          Recommended for use with KVM, or with other duplicative applications.
 245          See Documentation/vm/ksm.txt for more information: KSM is inactive
 246          until a program has madvised that an area is MADV_MERGEABLE, and
 247          root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 248
 249config DEFAULT_MMAP_MIN_ADDR
 250        int "Low address space to protect from user allocation"
 251        depends on MMU
 252        default 4096
 253        help
 254          This is the portion of low virtual memory which should be protected
 255          from userspace allocation.  Keeping a user from writing to low pages
 256          can help reduce the impact of kernel NULL pointer bugs.
 257
 258          For most ia64, ppc64 and x86 users with lots of address space
 259          a value of 65536 is reasonable and should cause no problems.
 260          On arm and other archs it should not be higher than 32768.
 261          Programs which use vm86 functionality or have some need to map
 262          this low address space will need CAP_SYS_RAWIO or disable this
 263          protection by setting the value to 0.
 264
 265          This value can be changed after boot using the
 266          /proc/sys/vm/mmap_min_addr tunable.
 267
 268config ARCH_SUPPORTS_MEMORY_FAILURE
 269        bool
 270
 271config MEMORY_FAILURE
 272        depends on MMU
 273        depends on ARCH_SUPPORTS_MEMORY_FAILURE
 274        bool "Enable recovery from hardware memory errors"
 275        help
 276          Enables code to recover from some memory failures on systems
 277          with MCA recovery. This allows a system to continue running
 278          even when some of its memory has uncorrected errors. This requires
 279          special hardware support and typically ECC memory.
 280
 281config HWPOISON_INJECT
 282        tristate "HWPoison pages injector"
 283        depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
 284        select PROC_PAGE_MONITOR
 285
 286config NOMMU_INITIAL_TRIM_EXCESS
 287        int "Turn on mmap() excess space trimming before booting"
 288        depends on !MMU
 289        default 1
 290        help
 291          The NOMMU mmap() frequently needs to allocate large contiguous chunks
 292          of memory on which to store mappings, but it can only ask the system
 293          allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 294          more than it requires.  To deal with this, mmap() is able to trim off
 295          the excess and return it to the allocator.
 296
 297          If trimming is enabled, the excess is trimmed off and returned to the
 298          system allocator, which can cause extra fragmentation, particularly
 299          if there are a lot of transient processes.
 300
 301          If trimming is disabled, the excess is kept, but not used, which for
 302          long-term mappings means that the space is wasted.
 303
 304          Trimming can be dynamically controlled through a sysctl option
 305          (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 306          excess pages there must be before trimming should occur, or zero if
 307          no trimming is to occur.
 308
 309          This option specifies the initial value of this option.  The default
 310          of 1 says that all excess pages should be trimmed.
 311
 312          See Documentation/nommu-mmap.txt for more information.
 313
 314config TRANSPARENT_HUGEPAGE
 315        bool "Transparent Hugepage Support"
 316        depends on X86 && MMU
 317        select COMPACTION
 318        help
 319          Transparent Hugepages allows the kernel to use huge pages and
 320          huge tlb transparently to the applications whenever possible.
 321          This feature can improve computing performance to certain
 322          applications by speeding up page faults during memory
 323          allocation, by reducing the number of tlb misses and by speeding
 324          up the pagetable walking.
 325
 326          If memory constrained on embedded, you may want to say N.
 327
 328choice
 329        prompt "Transparent Hugepage Support sysfs defaults"
 330        depends on TRANSPARENT_HUGEPAGE
 331        default TRANSPARENT_HUGEPAGE_ALWAYS
 332        help
 333          Selects the sysfs defaults for Transparent Hugepage Support.
 334
 335        config TRANSPARENT_HUGEPAGE_ALWAYS
 336                bool "always"
 337        help
 338          Enabling Transparent Hugepage always, can increase the
 339          memory footprint of applications without a guaranteed
 340          benefit but it will work automatically for all applications.
 341
 342        config TRANSPARENT_HUGEPAGE_MADVISE
 343                bool "madvise"
 344        help
 345          Enabling Transparent Hugepage madvise, will only provide a
 346          performance improvement benefit to the applications using
 347          madvise(MADV_HUGEPAGE) but it won't risk to increase the
 348          memory footprint of applications without a guaranteed
 349          benefit.
 350endchoice
 351
 352config CROSS_MEMORY_ATTACH
 353        bool "Cross Memory Support"
 354        depends on MMU
 355        default y
 356        help
 357          Enabling this option adds the system calls process_vm_readv and
 358          process_vm_writev which allow a process with the correct privileges
 359          to directly read from or write to to another process's address space.
 360          See the man page for more details.
 361
 362#
 363# UP and nommu archs use km based percpu allocator
 364#
 365config NEED_PER_CPU_KM
 366        depends on !SMP
 367        bool
 368        default y
 369
 370config CLEANCACHE
 371        bool "Enable cleancache driver to cache clean pages if tmem is present"
 372        default n
 373        help
 374          Cleancache can be thought of as a page-granularity victim cache
 375          for clean pages that the kernel's pageframe replacement algorithm
 376          (PFRA) would like to keep around, but can't since there isn't enough
 377          memory.  So when the PFRA "evicts" a page, it first attempts to use
 378          cleancache code to put the data contained in that page into
 379          "transcendent memory", memory that is not directly accessible or
 380          addressable by the kernel and is of unknown and possibly
 381          time-varying size.  And when a cleancache-enabled
 382          filesystem wishes to access a page in a file on disk, it first
 383          checks cleancache to see if it already contains it; if it does,
 384          the page is copied into the kernel and a disk access is avoided.
 385          When a transcendent memory driver is available (such as zcache or
 386          Xen transcendent memory), a significant I/O reduction
 387          may be achieved.  When none is available, all cleancache calls
 388          are reduced to a single pointer-compare-against-NULL resulting
 389          in a negligible performance hit.
 390
 391          If unsure, say Y to enable cleancache
 392
 393config FRONTSWAP
 394        bool "Enable frontswap to cache swap pages if tmem is present"
 395        depends on SWAP
 396        default n
 397        help
 398          Frontswap is so named because it can be thought of as the opposite
 399          of a "backing" store for a swap device.  The data is stored into
 400          "transcendent memory", memory that is not directly accessible or
 401          addressable by the kernel and is of unknown and possibly
 402          time-varying size.  When space in transcendent memory is available,
 403          a significant swap I/O reduction may be achieved.  When none is
 404          available, all frontswap calls are reduced to a single pointer-
 405          compare-against-NULL resulting in a negligible performance hit
 406          and swap data is stored as normal on the matching swap device.
 407
 408          If unsure, say Y to enable frontswap.
 409
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.