mm/Kconfig

   1 config SELECT_MEMORY_MODEL
   2         def_bool y
   3         depends on EXPERIMENTAL || ARCH_SELECT_MEMORY_MODEL
   4
   5 choice
   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
  12 config 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
  31 config 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
  47 config 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
  62 endchoice
  63
  64 config DISCONTIGMEM
  65         def_bool y
  66         depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
  67
  68 config SPARSEMEM
  69         def_bool y
  70         depends on SPARSEMEM_MANUAL
  71
  72 config FLATMEM
  73         def_bool y
  74         depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
  75
  76 config 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 #
  85 config NEED_MULTIPLE_NODES
  86         def_bool y
  87         depends on DISCONTIGMEM || NUMA
  88
  89 config 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 #
 103 config 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 #
 111 config SPARSEMEM_EXTREME
 112         def_bool y
 113         depends on SPARSEMEM && !SPARSEMEM_STATIC
 114
 115 config SPARSEMEM_VMEMMAP_ENABLE
 116         bool
 117
 118 config 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'
 128 config MEMORY_HOTPLUG
 129         bool "Allow for memory hot-add"
 130         depends on SPARSEMEM || X86_64_ACPI_NUMA
 131         depends on HOTPLUG && !(HIBERNATION && !S390) && ARCH_ENABLE_MEMORY_HOTPLUG
 132         depends on (IA64 || X86 || PPC64 || SUPERH || S390)
 133
 134 comment "Memory hotplug is currently incompatible with Software Suspend"
 135         depends on SPARSEMEM && HOTPLUG && HIBERNATION && !S390
 136
 137 config MEMORY_HOTPLUG_SPARSE
 138         def_bool y
 139         depends on SPARSEMEM && MEMORY_HOTPLUG
 140
 141 config MEMORY_HOTREMOVE
 142         bool "Allow for memory hot remove"
 143         depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 144         depends on MIGRATION
 145
 146 #
 147 # If we have space for more page flags then we can enable additional
 148 # optimizations and functionality.
 149 #
 150 # Regular Sparsemem takes page flag bits for the sectionid if it does not
 151 # use a virtual memmap. Disable extended page flags for 32 bit platforms
 152 # that require the use of a sectionid in the page flags.
 153 #
 154 config PAGEFLAGS_EXTENDED
 155         def_bool y
 156         depends on 64BIT || SPARSEMEM_VMEMMAP || !NUMA || !SPARSEMEM
 157
 158 # Heavily threaded applications may benefit from splitting the mm-wide
 159 # page_table_lock, so that faults on different parts of the user address
 160 # space can be handled with less contention: split it at this NR_CPUS.
 161 # Default to 4 for wider testing, though 8 might be more appropriate.
 162 # ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
 163 # PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
 164 #
 165 config SPLIT_PTLOCK_CPUS
 166         int
 167         default "4096" if ARM && !CPU_CACHE_VIPT
 168         default "4096" if PARISC && !PA20
 169         default "4"
 170
 171 #
 172 # support for page migration
 173 #
 174 config MIGRATION
 175         bool "Page migration"
 176         def_bool y
 177         depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE
 178         help
 179           Allows the migration of the physical location of pages of processes
 180           while the virtual addresses are not changed. This is useful for
 181           example on NUMA systems to put pages nearer to the processors accessing
 182           the page.
 183
 184 config PHYS_ADDR_T_64BIT
 185         def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
 186
 187 config ZONE_DMA_FLAG
 188         int
 189         default "0" if !ZONE_DMA
 190         default "1"
 191
 192 config BOUNCE
 193         def_bool y
 194         depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
 195
 196 config NR_QUICK
 197         int
 198         depends on QUICKLIST
 199         default "2" if SUPERH || AVR32
 200         default "1"
 201
 202 config VIRT_TO_BUS
 203         def_bool y
 204         depends on !ARCH_NO_VIRT_TO_BUS
 205
 206 config HAVE_MLOCK
 207         bool
 208         default y if MMU=y
 209
 210 config HAVE_MLOCKED_PAGE_BIT
 211         bool
 212         default y if HAVE_MLOCK=y
 213
 214 config MMU_NOTIFIER
 215         bool
 216
 217 config DEFAULT_MMAP_MIN_ADDR
 218         int "Low address space to protect from user allocation"
 219         default 4096
 220         help
 221           This is the portion of low virtual memory which should be protected
 222           from userspace allocation.  Keeping a user from writing to low pages
 223           can help reduce the impact of kernel NULL pointer bugs.
 224
 225           For most ia64, ppc64 and x86 users with lots of address space
 226           a value of 65536 is reasonable and should cause no problems.
 227           On arm and other archs it should not be higher than 32768.
 228           Programs which use vm86 functionality would either need additional
 229           permissions from either the LSM or the capabilities module or have
 230           this protection disabled.
 231
 232           This value can be changed after boot using the
 233           /proc/sys/vm/mmap_min_addr tunable.
 234
 235
 236 config NOMMU_INITIAL_TRIM_EXCESS
 237         int "Turn on mmap() excess space trimming before booting"
 238         depends on !MMU
 239         default 1
 240         help
 241           The NOMMU mmap() frequently needs to allocate large contiguous chunks
 242           of memory on which to store mappings, but it can only ask the system
 243           allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
 244           more than it requires.  To deal with this, mmap() is able to trim off
 245           the excess and return it to the allocator.
 246
 247           If trimming is enabled, the excess is trimmed off and returned to the
 248           system allocator, which can cause extra fragmentation, particularly
 249           if there are a lot of transient processes.
 250
 251           If trimming is disabled, the excess is kept, but not used, which for
 252           long-term mappings means that the space is wasted.
 253
 254           Trimming can be dynamically controlled through a sysctl option
 255           (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
 256           excess pages there must be before trimming should occur, or zero if
 257           no trimming is to occur.
 258
 259           This option specifies the initial value of this option.  The default
 260           of 1 says that all excess pages should be trimmed.
 261
 262           See Documentation/nommu-mmap.txt for more information.