config SELECT_MEMORY_MODEL def_bool y depends on 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 a 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 config HAVE_MEMBLOCK_NODE_MAP boolean config HAVE_MEMBLOCK_PHYS_MAP boolean config ARCH_DISCARD_MEMBLOCK boolean config NO_BOOTMEM boolean config MEMORY_ISOLATION boolean config MOVABLE_NODE boolean "Enable to assign a node which has only movable memory" depends on HAVE_MEMBLOCK depends on NO_BOOTMEM depends on X86_64 depends on NUMA default n help Allow a node to have only movable memory. Pages used by the kernel, such as direct mapping pages cannot be migrated. So the corresponding memory device cannot be hotplugged. This option allows the following two things: - When the system is booting, node full of hotpluggable memory can be arranged to have only movable memory so that the whole node can be hot-removed. (need movable_node boot option specified). - After the system is up, the option allows users to online all the memory of a node as movable memory so that the whole node can be hot-removed. Users who don't use the memory hotplug feature are fine with this option on since they don't specify movable_node boot option or they don't online memory as movable. Say Y here if you want to hotplug a whole node. Say N here if you want kernel to use memory on all nodes evenly. # # Only be set on architectures that have completely implemented memory hotplug # feature. If you are not sure, don't touch it. # config HAVE_BOOTMEM_INFO_NODE def_bool n # 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 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" select MEMORY_ISOLATION select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64) 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 !MMU default "999999" if ARM && !CPU_CACHE_VIPT default "999999" if PARISC && !PA20 default "4" config ARCH_ENABLE_SPLIT_PMD_PTLOCK boolean # # support for memory balloon compaction config BALLOON_COMPACTION bool "Allow for balloon memory compaction/migration" def_bool y depends on COMPACTION && VIRTIO_BALLOON help Memory fragmentation introduced by ballooning might reduce significantly the number of 2MB contiguous memory blocks that can be used within a guest, thus imposing performance penalties associated with the reduced number of transparent huge pages that could be used by the guest workload. Allowing the compaction & migration for memory pages enlisted as being part of memory balloon devices avoids the scenario aforementioned and helps improving memory defragmentation. # # support for memory compaction config COMPACTION bool "Allow for memory compaction" def_bool y select MIGRATION depends on 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 || COMPACTION || CMA) && MMU 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 ARCH_ENABLE_HUGEPAGE_MIGRATION boolean 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 bool "Enable bounce buffers" default y depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM) help Enable bounce buffers for devices that cannot access the full range of memory available to the CPU. Enabled by default when ZONE_DMA or HIGHMEM is selected, but you may say n to override this. # On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often # have more than 4GB of memory, but we don't currently use the IOTLB to present # a 32-bit address to OHCI. So we need to use a bounce pool instead. # # We also use the bounce pool to provide stable page writes for jbd. jbd # initiates buffer writeback without locking the page or setting PG_writeback, # and fixing that behavior (a second time; jbd2 doesn't have this problem) is # a major rework effort. Instead, use the bounce buffer to snapshot pages # (until jbd goes away). The only jbd user is ext3. config NEED_BOUNCE_POOL bool default y if (TILE && USB_OHCI_HCD) || (BLK_DEV_INTEGRITY && JBD) config NR_QUICK int depends on QUICKLIST default "2" if AVR32 default "1" config VIRT_TO_BUS bool help An architecture should select this if it implements the deprecated interface virt_to_bus(). All new architectures should probably not select this. 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" select MEMORY_ISOLATION 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. config TRANSPARENT_HUGEPAGE bool "Transparent Hugepage Support" depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE select COMPACTION help Transparent Hugepages allows the kernel to use huge pages and huge tlb transparently to the applications whenever possible. This feature can improve computing performance to certain applications by speeding up page faults during memory allocation, by reducing the number of tlb misses and by speeding up the pagetable walking. If memory constrained on embedded, you may want to say N. choice prompt "Transparent Hugepage Support sysfs defaults" depends on TRANSPARENT_HUGEPAGE default TRANSPARENT_HUGEPAGE_ALWAYS help Selects the sysfs defaults for Transparent Hugepage Support. config TRANSPARENT_HUGEPAGE_ALWAYS bool "always" help Enabling Transparent Hugepage always, can increase the memory footprint of applications without a guaranteed benefit but it will work automatically for all applications. config TRANSPARENT_HUGEPAGE_MADVISE bool "madvise" help Enabling Transparent Hugepage madvise, will only provide a performance improvement benefit to the applications using madvise(MADV_HUGEPAGE) but it won't risk to increase the memory footprint of applications without a guaranteed benefit. endchoice # # UP and nommu archs use km based percpu allocator # config NEED_PER_CPU_KM depends on !SMP bool default y config CLEANCACHE bool "Enable cleancache driver to cache clean pages if tmem is present" default n help Cleancache can be thought of as a page-granularity victim cache for clean pages that the kernel's pageframe replacement algorithm (PFRA) would like to keep around, but can't since there isn't enough memory. So when the PFRA "evicts" a page, it first attempts to use cleancache code to put the data contained in that page into "transcendent memory", memory that is not directly accessible or addressable by the kernel and is of unknown and possibly time-varying size. And when a cleancache-enabled filesystem wishes to access a page in a file on disk, it first checks cleancache to see if it already contains it; if it does, the page is copied into the kernel and a disk access is avoided. When a transcendent memory driver is available (such as zcache or Xen transcendent memory), a significant I/O reduction may be achieved. When none is available, all cleancache calls are reduced to a single pointer-compare-against-NULL resulting in a negligible performance hit. If unsure, say Y to enable cleancache config FRONTSWAP bool "Enable frontswap to cache swap pages if tmem is present" depends on SWAP default n help Frontswap is so named because it can be thought of as the opposite of a "backing" store for a swap device. The data is stored into "transcendent memory", memory that is not directly accessible or addressable by the kernel and is of unknown and possibly time-varying size. When space in transcendent memory is available, a significant swap I/O reduction may be achieved. When none is available, all frontswap calls are reduced to a single pointer- compare-against-NULL resulting in a negligible performance hit and swap data is stored as normal on the matching swap device. If unsure, say Y to enable frontswap. config CMA bool "Contiguous Memory Allocator" depends on HAVE_MEMBLOCK && MMU select MIGRATION select MEMORY_ISOLATION help This enables the Contiguous Memory Allocator which allows other subsystems to allocate big physically-contiguous blocks of memory. CMA reserves a region of memory and allows only movable pages to be allocated from it. This way, the kernel can use the memory for pagecache and when a subsystem requests for contiguous area, the allocated pages are migrated away to serve the contiguous request. If unsure, say "n". config CMA_DEBUG bool "CMA debug messages (DEVELOPMENT)" depends on DEBUG_KERNEL && CMA help Turns on debug messages in CMA. This produces KERN_DEBUG messages for every CMA call as well as various messages while processing calls such as dma_alloc_from_contiguous(). This option does not affect warning and error messages. config ZBUD tristate default n help A special purpose allocator for storing compressed pages. It is designed to store up to two compressed pages per physical page. While this design limits storage density, it has simple and deterministic reclaim properties that make it preferable to a higher density approach when reclaim will be used. config ZSWAP bool "Compressed cache for swap pages (EXPERIMENTAL)" depends on FRONTSWAP && CRYPTO=y select CRYPTO_LZO select ZBUD default n help A lightweight compressed cache for swap pages. It takes pages that are in the process of being swapped out and attempts to compress them into a dynamically allocated RAM-based memory pool. This can result in a significant I/O reduction on swap device and, in the case where decompressing from RAM is faster that swap device reads, can also improve workload performance. This is marked experimental because it is a new feature (as of v3.11) that interacts heavily with memory reclaim. While these interactions don't cause any known issues on simple memory setups, they have not be fully explored on the large set of potential configurations and workloads that exist. config MEM_SOFT_DIRTY bool "Track memory changes" depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS select PROC_PAGE_MONITOR help This option enables memory changes tracking by introducing a soft-dirty bit on pte-s. This bit it set when someone writes into a page just as regular dirty bit, but unlike the latter it can be cleared by hands. See Documentation/vm/soft-dirty.txt for more details. config ZSMALLOC tristate "Memory allocator for compressed pages" depends on MMU default n help zsmalloc is a slab-based memory allocator designed to store compressed RAM pages. zsmalloc uses virtual memory mapping in order to reduce fragmentation. However, this results in a non-standard allocator interface where a handle, not a pointer, is returned by an alloc(). This handle must be mapped in order to access the allocated space. config PGTABLE_MAPPING bool "Use page table mapping to access object in zsmalloc" depends on ZSMALLOC help By default, zsmalloc uses a copy-based object mapping method to access allocations that span two pages. However, if a particular architecture (ex, ARM) performs VM mapping faster than copying, then you should select this. This causes zsmalloc to use page table mapping rather than copying for object mapping. You can check speed with zsmalloc benchmark: https://github.com/spartacus06/zsmapbench config GENERIC_EARLY_IOREMAP bool config MAX_STACK_SIZE_MB int "Maximum user stack size for 32-bit processes (MB)" default 80 range 8 256 if METAG range 8 2048 depends on STACK_GROWSUP && (!64BIT || COMPAT) help This is the maximum stack size in Megabytes in the VM layout of 32-bit user processes when the stack grows upwards (currently only on parisc and metag arch). The stack will be located at the highest memory address minus the given value, unless the RLIMIT_STACK hard limit is changed to a smaller value in which case that is used. A sane initial value is 80 MB.