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 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_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. # 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 && !HIBERNATION && ARCH_ENABLE_MEMORY_HOTPLUG depends on (IA64 || X86 || PPC64 || SUPERH || S390) comment "Memory hotplug is currently incompatible with Software Suspend" depends on SPARSEMEM && HOTPLUG && HIBERNATION 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 || !NUMA || !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. # config SPLIT_PTLOCK_CPUS int default "4096" if ARM && !CPU_CACHE_VIPT default "4096" if PARISC && !PA20 default "4" # # 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 for example on NUMA systems to put pages nearer to the processors accessing the page. 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 SUPERH || AVR32 default "1" config VIRT_TO_BUS def_bool y depends on !ARCH_NO_VIRT_TO_BUS config UNEVICTABLE_LRU bool "Add LRU list to track non-evictable pages" default y help Keeps unevictable pages off of the active and inactive pageout lists, so kswapd will not waste CPU time or have its balancing algorithms thrown off by scanning these pages. Selecting this will use one page flag and increase the code size a little, say Y unless you know what you are doing. See Documentation/vm/unevictable-lru.txt for more information. config HAVE_MLOCK bool default y if MMU=y config HAVE_MLOCKED_PAGE_BIT bool default y if HAVE_MLOCK=y && UNEVICTABLE_LRU=y config MMU_NOTIFIER bool config DEFAULT_MMAP_MIN_ADDR int "Low address space to protect from user allocation" 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 would either need additional permissions from either the LSM or the capabilities module or have this protection disabled. This value can be changed after boot using the /proc/sys/vm/mmap_min_addr tunable. 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.