linux-imx/mm/Kconfig

config SELECT_MEMORY_MODEL def_bool y depends on EXPERIMENTAL || ARCH_SELECT_MEMORY_MODEL

choice prompt "Memory model" depends on SELECT_MEMORY_MODEL default DISCONTIGMEM_MANUAL if ARCH_DISCONTIGMEM_DEFAULT default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT default FLATMEM_MANUAL

config FLATMEM_MANUAL bool "Flat Memory" depends on !(ARCH_DISCONTIGMEM_ENABLE || ARCH_SPARSEMEM_ENABLE) || ARCH_FLATMEM_ENABLE help This option allows you to change some of the ways that Linux manages its memory internally. Most users will only have one option here: FLATMEM. This is normal and a correct option.

  Some users of more advanced features like NUMA and
  memory hotplug may have different options here.
  DISCONTIGMEM is an more mature, better tested system,
  but is incompatible with memory hotplug and may suffer
  decreased performance over SPARSEMEM.  If unsure between
  "Sparse Memory" and "Discontiguous Memory", choose
  "Discontiguous Memory".

  If unsure, choose this option (Flat Memory) over any other.

config DISCONTIGMEM_MANUAL bool "Discontiguous Memory" depends on ARCH_DISCONTIGMEM_ENABLE help This option provides enhanced support for discontiguous memory systems, over FLATMEM. These systems have holes in their physical address spaces, and this option provides more efficient handling of these holes. However, the vast majority of hardware has quite flat address spaces, and can have degraded performance from the extra overhead that this option imposes.

  Many NUMA configurations will have this as the only option.

  If unsure, choose "Flat Memory" over this option.

config SPARSEMEM_MANUAL bool "Sparse Memory" depends on ARCH_SPARSEMEM_ENABLE help This will be the only option for some systems, including memory hotplug systems. This is normal.

  For many other systems, this will be an alternative to
  "Discontiguous Memory".  This option provides some potential
  performance benefits, along with decreased code complexity,
  but it is newer, and more experimental.

  If unsure, choose "Discontiguous Memory" or "Flat Memory"
  over this option.

endchoice

config DISCONTIGMEM def_bool y depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL

config SPARSEMEM def_bool y depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL

config FLATMEM def_bool y depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL

config FLAT_NODE_MEM_MAP def_bool y depends on !SPARSEMEM

Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's

to represent different areas of memory. This variable allows

those dependencies to exist individually.

config NEED_MULTIPLE_NODES def_bool y depends on DISCONTIGMEM || NUMA

config HAVE_MEMORY_PRESENT def_bool y depends on ARCH_HAVE_MEMORY_PRESENT || SPARSEMEM

SPARSEMEM_EXTREME (which is the default) does some bootmem

allocations when memory_present() is called. If this cannot

be done on your architecture, select this option. However,

statically allocating the mem_section[] array can potentially

consume vast quantities of .bss, so be careful.

This option will also potentially produce smaller runtime code

with gcc 3.4 and later.

config SPARSEMEM_STATIC bool

Architecture platforms which require a two level mem_section in SPARSEMEM

must select this option. This is usually for architecture platforms with

an extremely sparse physical address space.

config SPARSEMEM_EXTREME def_bool y depends on SPARSEMEM && !SPARSEMEM_STATIC

config SPARSEMEM_VMEMMAP_ENABLE bool

config SPARSEMEM_ALLOC_MEM_MAP_TOGETHER def_bool y depends on SPARSEMEM && X86_64

config SPARSEMEM_VMEMMAP bool "Sparse Memory virtual memmap" depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE default y help SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise pfn_to_page and page_to_pfn operations. This is the most efficient option when sufficient kernel resources are available.

config HAVE_MEMBLOCK boolean

eventually, we can have this option just 'select SPARSEMEM'

config MEMORY_HOTPLUG bool "Allow for memory hot-add" depends on SPARSEMEM || X86_64_ACPI_NUMA depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)

config MEMORY_HOTPLUG_SPARSE def_bool y depends on SPARSEMEM && MEMORY_HOTPLUG

config MEMORY_HOTREMOVE bool "Allow for memory hot remove" depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE depends on MIGRATION

If we have space for more page flags then we can enable additional

optimizations and functionality.

Regular Sparsemem takes page flag bits for the sectionid if it does not

use a virtual memmap. Disable extended page flags for 32 bit platforms

that require the use of a sectionid in the page flags.

config PAGEFLAGS_EXTENDED def_bool y depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM

Heavily threaded applications may benefit from splitting the mm-wide

page_table_lock, so that faults on different parts of the user address

space can be handled with less contention: split it at this NR_CPUS.

Default to 4 for wider testing, though 8 might be more appropriate.

ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.

PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.

DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.

config SPLIT_PTLOCK_CPUS int default "999999" if ARM && !CPU_CACHE_VIPT default "999999" if PARISC && !PA20 default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC default "4"

support for memory compaction

config COMPACTION bool "Allow for memory compaction" select MIGRATION depends on EXPERIMENTAL && HUGETLB_PAGE && MMU help Allows the compaction of memory for the allocation of huge pages.

support for page migration

config MIGRATION bool "Page migration" def_bool y depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE help Allows the migration of the physical location of pages of processes while the virtual addresses are not changed. This is useful in two situations. The first is on NUMA systems to put pages nearer to the processors accessing. The second is when allocating huge pages as migration can relocate pages to satisfy a huge page allocation instead of reclaiming.

config PHYS_ADDR_T_64BIT def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT

config ZONE_DMA_FLAG int default "0" if !ZONE_DMA default "1"

config BOUNCE def_bool y depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)

config NR_QUICK int depends on QUICKLIST default "2" if AVR32 default "1"

config VIRT_TO_BUS def_bool y depends on !ARCH_NO_VIRT_TO_BUS

config MMU_NOTIFIER bool

config KSM bool "Enable KSM for page merging" depends on MMU help Enable Kernel Samepage Merging: KSM periodically scans those areas of an application's address space that an app has advised may be mergeable. When it finds pages of identical content, it replaces the many instances by a single page with that content, so saving memory until one or another app needs to modify the content. Recommended for use with KVM, or with other duplicative applications. See Documentation/vm/ksm.txt for more information: KSM is inactive until a program has madvised that an area is MADV_MERGEABLE, and root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).

config DEFAULT_MMAP_MIN_ADDR int "Low address space to protect from user allocation" depends on MMU default 4096 help This is the portion of low virtual memory which should be protected from userspace allocation. Keeping a user from writing to low pages can help reduce the impact of kernel NULL pointer bugs.

  For most ia64, ppc64 and x86 users with lots of address space
  a value of 65536 is reasonable and should cause no problems.
  On arm and other archs it should not be higher than 32768.
  Programs which use vm86 functionality or have some need to map
  this low address space will need CAP_SYS_RAWIO or disable this
  protection by setting the value to 0.

  This value can be changed after boot using the
  /proc/sys/vm/mmap_min_addr tunable.

config ARCH_SUPPORTS_MEMORY_FAILURE bool

config MEMORY_FAILURE depends on MMU depends on ARCH_SUPPORTS_MEMORY_FAILURE bool "Enable recovery from hardware memory errors" help Enables code to recover from some memory failures on systems with MCA recovery. This allows a system to continue running even when some of its memory has uncorrected errors. This requires special hardware support and typically ECC memory.

config HWPOISON_INJECT tristate "HWPoison pages injector" depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS select PROC_PAGE_MONITOR

config NOMMU_INITIAL_TRIM_EXCESS int "Turn on mmap() excess space trimming before booting" depends on !MMU default 1 help The NOMMU mmap() frequently needs to allocate large contiguous chunks of memory on which to store mappings, but it can only ask the system allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently more than it requires. To deal with this, mmap() is able to trim off the excess and return it to the allocator.

  If trimming is enabled, the excess is trimmed off and returned to the
  system allocator, which can cause extra fragmentation, particularly
  if there are a lot of transient processes.

  If trimming is disabled, the excess is kept, but not used, which for
  long-term mappings means that the space is wasted.

  Trimming can be dynamically controlled through a sysctl option
  (/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
  excess pages there must be before trimming should occur, or zero if
  no trimming is to occur.

  This option specifies the initial value of this option.  The default
  of 1 says that all excess pages should be trimmed.

  See Documentation/nommu-mmap.txt for more information.