linux-yocto/mm/Kconfig

SPDX-License-Identifier: GPL-2.0-only

menu "Memory Management options"

For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can

add proper SWAP support to them, in which case this can be remove.

config ARCH_NO_SWAP bool

config ZPOOL bool

menuconfig SWAP bool "Support for paging of anonymous memory (swap)" depends on MMU && BLOCK && !ARCH_NO_SWAP default y help This option allows you to choose whether you want to have support for so called swap devices or swap files in your kernel that are used to provide more virtual memory than the actual RAM present in your computer. If unsure say Y.

config ZSWAP bool "Compressed cache for swap pages" depends on SWAP select CRYPTO select ZPOOL 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 than swap device reads, can also improve workload performance.

config ZSWAP_DEFAULT_ON bool "Enable the compressed cache for swap pages by default" depends on ZSWAP help If selected, the compressed cache for swap pages will be enabled at boot, otherwise it will be disabled.

  The selection made here can be overridden by using the kernel
  command line 'zswap.enabled=' option.

config ZSWAP_SHRINKER_DEFAULT_ON bool "Shrink the zswap pool on memory pressure" depends on ZSWAP default n help If selected, the zswap shrinker will be enabled, and the pages stored in the zswap pool will become available for reclaim (i.e written back to the backing swap device) on memory pressure.

  This means that zswap writeback could happen even if the pool is
  not yet full, or the cgroup zswap limit has not been reached,
  reducing the chance that cold pages will reside in the zswap pool
  and consume memory indefinitely.

choice prompt "Default compressor" depends on ZSWAP default ZSWAP_COMPRESSOR_DEFAULT_LZO help Selects the default compression algorithm for the compressed cache for swap pages.

  For an overview what kind of performance can be expected from
  a particular compression algorithm please refer to the benchmarks
  available at the following LWN page:
  https://lwn.net/Articles/751795/

  If in doubt, select 'LZO'.

  The selection made here can be overridden by using the kernel
  command line 'zswap.compressor=' option.

config ZSWAP_COMPRESSOR_DEFAULT_DEFLATE bool "Deflate" select CRYPTO_DEFLATE help Use the Deflate algorithm as the default compression algorithm.

config ZSWAP_COMPRESSOR_DEFAULT_LZO bool "LZO" select CRYPTO_LZO help Use the LZO algorithm as the default compression algorithm.

config ZSWAP_COMPRESSOR_DEFAULT_842 bool "842" select CRYPTO_842 help Use the 842 algorithm as the default compression algorithm.

config ZSWAP_COMPRESSOR_DEFAULT_LZ4 bool "LZ4" select CRYPTO_LZ4 help Use the LZ4 algorithm as the default compression algorithm.

config ZSWAP_COMPRESSOR_DEFAULT_LZ4HC bool "LZ4HC" select CRYPTO_LZ4HC help Use the LZ4HC algorithm as the default compression algorithm.

config ZSWAP_COMPRESSOR_DEFAULT_ZSTD bool "zstd" select CRYPTO_ZSTD help Use the zstd algorithm as the default compression algorithm. endchoice

config ZSWAP_COMPRESSOR_DEFAULT string depends on ZSWAP default "deflate" if ZSWAP_COMPRESSOR_DEFAULT_DEFLATE default "lzo" if ZSWAP_COMPRESSOR_DEFAULT_LZO default "842" if ZSWAP_COMPRESSOR_DEFAULT_842 default "lz4" if ZSWAP_COMPRESSOR_DEFAULT_LZ4 default "lz4hc" if ZSWAP_COMPRESSOR_DEFAULT_LZ4HC default "zstd" if ZSWAP_COMPRESSOR_DEFAULT_ZSTD default ""

choice prompt "Default allocator" depends on ZSWAP default ZSWAP_ZPOOL_DEFAULT_ZSMALLOC if MMU help Selects the default allocator for the compressed cache for swap pages. The default is 'zbud' for compatibility, however please do read the description of each of the allocators below before making a right choice.

  The selection made here can be overridden by using the kernel
  command line 'zswap.zpool=' option.

config ZSWAP_ZPOOL_DEFAULT_ZSMALLOC bool "zsmalloc" select ZSMALLOC help Use the zsmalloc allocator as the default allocator. endchoice

config ZSWAP_ZPOOL_DEFAULT string depends on ZSWAP default "zsmalloc" if ZSWAP_ZPOOL_DEFAULT_ZSMALLOC default ""

config ZSMALLOC tristate prompt "N:1 compression allocator (zsmalloc)" if (ZSWAP || ZRAM) depends on MMU help zsmalloc is a slab-based memory allocator designed to store pages of various compression levels efficiently. It achieves the highest storage density with the least amount of fragmentation.

config ZSMALLOC_STAT bool "Export zsmalloc statistics" depends on ZSMALLOC select DEBUG_FS help This option enables code in the zsmalloc to collect various statistics about what's happening in zsmalloc and exports that information to userspace via debugfs. If unsure, say N.

config ZSMALLOC_CHAIN_SIZE int "Maximum number of physical pages per-zspage" default 8 range 4 16 depends on ZSMALLOC help This option sets the upper limit on the number of physical pages that a zmalloc page (zspage) can consist of. The optimal zspage chain size is calculated for each size class during the initialization of the pool.

  Changing this option can alter the characteristics of size classes,
  such as the number of pages per zspage and the number of objects
  per zspage. This can also result in different configurations of
  the pool, as zsmalloc merges size classes with similar
  characteristics.

  For more information, see zsmalloc documentation.

menu "Slab allocator options"

config SLUB def_bool y

config KVFREE_RCU_BATCHED def_bool y depends on !SLUB_TINY && !TINY_RCU

config SLUB_TINY bool "Configure for minimal memory footprint" depends on EXPERT && !COMPILE_TEST select SLAB_MERGE_DEFAULT help Configures the slab allocator in a way to achieve minimal memory footprint, sacrificing scalability, debugging and other features. This is intended only for the smallest system that had used the SLOB allocator and is not recommended for systems with more than 16MB RAM.

   If unsure, say N.

config SLAB_MERGE_DEFAULT bool "Allow slab caches to be merged" default y help For reduced kernel memory fragmentation, slab caches can be merged when they share the same size and other characteristics. This carries a risk of kernel heap overflows being able to overwrite objects from merged caches (and more easily control cache layout), which makes such heap attacks easier to exploit by attackers. By keeping caches unmerged, these kinds of exploits can usually only damage objects in the same cache. To disable merging at runtime, "slab_nomerge" can be passed on the kernel command line.

config SLAB_FREELIST_RANDOM bool "Randomize slab freelist" depends on !SLUB_TINY help Randomizes the freelist order used on creating new pages. This security feature reduces the predictability of the kernel slab allocator against heap overflows.

config SLAB_FREELIST_HARDENED bool "Harden slab freelist metadata" depends on !SLUB_TINY help Many kernel heap attacks try to target slab cache metadata and other infrastructure. This options makes minor performance sacrifices to harden the kernel slab allocator against common freelist exploit methods.

config SLAB_BUCKETS bool "Support allocation from separate kmalloc buckets" depends on !SLUB_TINY default SLAB_FREELIST_HARDENED help Kernel heap attacks frequently depend on being able to create specifically-sized allocations with user-controlled contents that will be allocated into the same kmalloc bucket as a target object. To avoid sharing these allocation buckets, provide an explicitly separated set of buckets to be used for user-controlled allocations. This may very slightly increase memory fragmentation, though in practice it's only a handful of extra pages since the bulk of user-controlled allocations are relatively long-lived.

  If unsure, say Y.

config SLUB_STATS default n bool "Enable performance statistics" depends on SYSFS && !SLUB_TINY help The statistics are useful to debug slab allocation behavior in order find ways to optimize the allocator. This should never be enabled for production use since keeping statistics slows down the allocator by a few percentage points. The slabinfo command supports the determination of the most active slabs to figure out which slabs are relevant to a particular load. Try running: slabinfo -DA

config SLUB_CPU_PARTIAL default y depends on SMP && !SLUB_TINY bool "Enable per cpu partial caches" help Per cpu partial caches accelerate objects allocation and freeing that is local to a processor at the price of more indeterminism in the latency of the free. On overflow these caches will be cleared which requires the taking of locks that may cause latency spikes. Typically one would choose no for a realtime system.

config RANDOM_KMALLOC_CACHES default n depends on !SLUB_TINY bool "Randomize slab caches for normal kmalloc" help A hardening feature that creates multiple copies of slab caches for normal kmalloc allocation and makes kmalloc randomly pick one based on code address, which makes the attackers more difficult to spray vulnerable memory objects on the heap for the purpose of exploiting memory vulnerabilities.

  Currently the number of copies is set to 16, a reasonably large value
  that effectively diverges the memory objects allocated for different
  subsystems or modules into different caches, at the expense of a
  limited degree of memory and CPU overhead that relates to hardware and
  system workload.

endmenu # Slab allocator options

config SHUFFLE_PAGE_ALLOCATOR bool "Page allocator randomization" default SLAB_FREELIST_RANDOM && ACPI_NUMA help Randomization of the page allocator improves the average utilization of a direct-mapped memory-side-cache. See section 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI 6.2a specification for an example of how a platform advertises the presence of a memory-side-cache. There are also incidental security benefits as it reduces the predictability of page allocations to compliment SLAB_FREELIST_RANDOM, but the default granularity of shuffling on the MAX_PAGE_ORDER i.e, 10th order of pages is selected based on cache utilization benefits on x86.

  While the randomization improves cache utilization it may
  negatively impact workloads on platforms without a cache. For
  this reason, by default, the randomization is not enabled even
  if SHUFFLE_PAGE_ALLOCATOR=y. The randomization may be force enabled
  with the 'page_alloc.shuffle' kernel command line parameter.

  Say Y if unsure.

config COMPAT_BRK bool "Disable heap randomization" default y help Randomizing heap placement makes heap exploits harder, but it also breaks ancient binaries (including anything libc5 based). This option changes the bootup default to heap randomization disabled, and can be overridden at runtime by setting /proc/sys/kernel/randomize_va_space to 2.

  On non-ancient distros (post-2000 ones) N is usually a safe choice.

config MMAP_ALLOW_UNINITIALIZED bool "Allow mmapped anonymous memory to be uninitialized" depends on EXPERT && !MMU default n help Normally, and according to the Linux spec, anonymous memory obtained from mmap() has its contents cleared before it is passed to userspace. Enabling this config option allows you to request that mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus providing a huge performance boost. If this option is not enabled, then the flag will be ignored.

  This is taken advantage of by uClibc's malloc(), and also by
  ELF-FDPIC binfmt's brk and stack allocator.

  Because of the obvious security issues, this option should only be
  enabled on embedded devices where you control what is run in
  userspace.  Since that isn't generally a problem on no-MMU systems,
  it is normally safe to say Y here.

  See Documentation/admin-guide/mm/nommu-mmap.rst for more information.

config SELECT_MEMORY_MODEL def_bool y depends on ARCH_SELECT_MEMORY_MODEL

choice prompt "Memory model" depends on SELECT_MEMORY_MODEL default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT default FLATMEM_MANUAL 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 selected by the architecture configuration. This is normal.

config FLATMEM_MANUAL bool "Flat Memory" depends on !ARCH_SPARSEMEM_ENABLE || ARCH_FLATMEM_ENABLE help This option is best suited for non-NUMA systems with flat address space. The FLATMEM is the most efficient system in terms of performance and resource consumption and it is the best option for smaller systems.

  For systems that have holes in their physical address
  spaces and for features like NUMA and memory hotplug,
  choose "Sparse Memory".

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

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

  This option provides efficient support for systems with
  holes is their physical address space and allows memory
  hot-plug and hot-remove.

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

endchoice

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

config FLATMEM def_bool y depends on !SPARSEMEM || FLATMEM_MANUAL

SPARSEMEM_EXTREME (which is the default) does some bootmem

allocations when sparse_init() 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.

config SPARSEMEM_VMEMMAP_PREINIT bool

Select this config option from the architecture Kconfig, if it is preferred

to enable the feature of HugeTLB/dev_dax vmemmap optimization.

config ARCH_WANT_OPTIMIZE_DAX_VMEMMAP bool

config ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP bool

config ARCH_WANT_HUGETLB_VMEMMAP_PREINIT bool

config HAVE_MEMBLOCK_PHYS_MAP bool

config HAVE_GUP_FAST depends on MMU bool

Enable memblock support for scratch memory which is needed for kexec handover

config MEMBLOCK_KHO_SCRATCH bool

Don't discard allocated memory used to track "memory" and "reserved" memblocks

after early boot, so it can still be used to test for validity of memory.

Also, memblocks are updated with memory hot(un)plug.

config ARCH_KEEP_MEMBLOCK bool

Keep arch NUMA mapping infrastructure post-init.

config NUMA_KEEP_MEMINFO bool

config MEMORY_ISOLATION bool

IORESOURCE_SYSTEM_RAM regions in the kernel resource tree that are marked

IORESOURCE_EXCLUSIVE cannot be mapped to user space, for example, via

/dev/mem.

config EXCLUSIVE_SYSTEM_RAM def_bool y depends on !DEVMEM || STRICT_DEVMEM

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

config ARCH_ENABLE_MEMORY_HOTPLUG bool

config ARCH_ENABLE_MEMORY_HOTREMOVE bool

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

menuconfig MEMORY_HOTPLUG bool "Memory hotplug" select MEMORY_ISOLATION depends on SPARSEMEM depends on ARCH_ENABLE_MEMORY_HOTPLUG depends on 64BIT select NUMA_KEEP_MEMINFO if NUMA

if MEMORY_HOTPLUG

choice prompt "Memory Hotplug Default Online Type" default MHP_DEFAULT_ONLINE_TYPE_OFFLINE help Default memory type for hotplugged memory.

  This option sets the default policy setting for memory hotplug
  onlining policy (/sys/devices/system/memory/auto_online_blocks) which
  determines what happens to newly added memory regions. Policy setting
  can always be changed at runtime.

  The default is 'offline'.

  Select offline to defer onlining to drivers and user policy.
  Select auto to let the kernel choose what zones to utilize.
  Select online_kernel to generally allow kernel usage of this memory.
  Select online_movable to generally disallow kernel usage of this memory.

  Example kernel usage would be page structs and page tables.

  See Documentation/admin-guide/mm/memory-hotplug.rst for more information.

config MHP_DEFAULT_ONLINE_TYPE_OFFLINE bool "offline" help Hotplugged memory will not be onlined by default. Choose this for systems with drivers and user policy that handle onlining of hotplug memory policy.

config MHP_DEFAULT_ONLINE_TYPE_ONLINE_AUTO bool "auto" help Select this if you want the kernel to automatically online hotplugged memory into the zone it thinks is reasonable. This memory may be utilized for kernel data.

config MHP_DEFAULT_ONLINE_TYPE_ONLINE_KERNEL bool "kernel" help Select this if you want the kernel to automatically online hotplugged memory into a zone capable of being used for kernel data. This typically means ZONE_NORMAL.

config MHP_DEFAULT_ONLINE_TYPE_ONLINE_MOVABLE bool "movable" help Select this if you want the kernel to automatically online hotplug memory into ZONE_MOVABLE. This memory will generally not be utilized for kernel data.

  This should only be used when the admin knows sufficient
  ZONE_NORMAL memory is available to describe hotplug memory,
  otherwise hotplug memory may fail to online. For example,
  sufficient kernel-capable memory (ZONE_NORMAL) must be
  available to allocate page structs to describe ZONE_MOVABLE.

endchoice

config MEMORY_HOTREMOVE bool "Allow for memory hot remove" select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64) depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE depends on MIGRATION

config MHP_MEMMAP_ON_MEMORY def_bool y depends on MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP depends on ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE

endif # MEMORY_HOTPLUG

config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE bool

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.

SPARC32 allocates multiple pte tables within a single page, and therefore

a per-page lock leads to problems when multiple tables need to be locked

at the same time (e.g. copy_page_range()).

DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.

config SPLIT_PTE_PTLOCKS def_bool y depends on MMU depends on SMP depends on NR_CPUS >= 4 depends on !ARM || CPU_CACHE_VIPT depends on !PARISC || PA20 depends on !SPARC32

config ARCH_ENABLE_SPLIT_PMD_PTLOCK bool

config SPLIT_PMD_PTLOCKS def_bool y depends on SPLIT_PTE_PTLOCKS && ARCH_ENABLE_SPLIT_PMD_PTLOCK

support for memory balloon

config MEMORY_BALLOON bool

support for memory balloon compaction

config BALLOON_COMPACTION bool "Allow for balloon memory compaction/migration" default y depends on COMPACTION && MEMORY_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" default y select MIGRATION depends on MMU help Compaction is the only memory management component to form high order (larger physically contiguous) memory blocks reliably. The page allocator relies on compaction heavily and the lack of the feature can lead to unexpected OOM killer invocations for high order memory requests. You shouldn't disable this option unless there really is a strong reason for it and then we would be really interested to hear about that at linux-mm@kvack.org.

config COMPACT_UNEVICTABLE_DEFAULT int depends on COMPACTION default 0 if PREEMPT_RT default 1

support for free page reporting

config PAGE_REPORTING bool "Free page reporting" help Free page reporting allows for the incremental acquisition of free pages from the buddy allocator for the purpose of reporting those pages to another entity, such as a hypervisor, so that the memory can be freed within the host for other uses.

support for page migration

config MIGRATION bool "Page migration" default 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 DEVICE_MIGRATION def_bool MIGRATION && ZONE_DEVICE

config ARCH_ENABLE_HUGEPAGE_MIGRATION bool

config ARCH_ENABLE_THP_MIGRATION bool

config HUGETLB_PAGE_SIZE_VARIABLE def_bool n help Allows the pageblock_order value to be dynamic instead of just standard HUGETLB_PAGE_ORDER when there are multiple HugeTLB page sizes available on a platform.

  Note that the pageblock_order cannot exceed MAX_PAGE_ORDER and will be
  clamped down to MAX_PAGE_ORDER.

config CONTIG_ALLOC def_bool (MEMORY_ISOLATION && COMPACTION) || CMA

config PCP_BATCH_SCALE_MAX int "Maximum scale factor of PCP (Per-CPU pageset) batch allocate/free" default 5 range 0 6 help In page allocator, PCP (Per-CPU pageset) is refilled and drained in batches. The batch number is scaled automatically to improve page allocation/free throughput. But too large scale factor may hurt latency. This option sets the upper limit of scale factor to limit the maximum latency.

config PHYS_ADDR_T_64BIT def_bool 64BIT

config BOUNCE bool "Enable bounce buffers" default y depends on BLOCK && MMU && HIGHMEM help Enable bounce buffers for devices that cannot access the full range of memory available to the CPU. Enabled by default when HIGHMEM is selected, but you may say n to override this.

config MMU_NOTIFIER bool select INTERVAL_TREE

config KSM bool "Enable KSM for page merging" depends on MMU select XXHASH 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/mm/ksm.rst 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 arm64, 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 select RAS 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/admin-guide/mm/nommu-mmap.rst for more information.

config ARCH_WANT_GENERAL_HUGETLB bool

config ARCH_WANTS_THP_SWAP def_bool n

config MM_ID def_bool n

menuconfig TRANSPARENT_HUGEPAGE bool "Transparent Hugepage Support" depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE && !PREEMPT_RT select COMPACTION select XARRAY_MULTI select MM_ID 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.

if TRANSPARENT_HUGEPAGE

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.

config TRANSPARENT_HUGEPAGE_NEVER
	bool "never"
help
  Disable Transparent Hugepage by default. It can still be
  enabled at runtime via sysfs.

endchoice

config THP_SWAP def_bool y depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP && 64BIT help Swap transparent huge pages in one piece, without splitting. XXX: For now, swap cluster backing transparent huge page will be split after swapout.

  For selection by architectures with reasonable THP sizes.

config READ_ONLY_THP_FOR_FS bool "Read-only THP for filesystems (EXPERIMENTAL)" depends on TRANSPARENT_HUGEPAGE

help
  Allow khugepaged to put read-only file-backed pages in THP.

  This is marked experimental because it is a new feature. Write
  support of file THPs will be developed in the next few release
  cycles.

config NO_PAGE_MAPCOUNT bool "No per-page mapcount (EXPERIMENTAL)" help Do not maintain per-page mapcounts for pages part of larger allocations, such as transparent huge pages.

  When this config option is enabled, some interfaces that relied on
  this information will rely on less-precise per-allocation information
  instead: for example, using the average per-page mapcount in such
  a large allocation instead of the per-page mapcount.

  EXPERIMENTAL because the impact of some changes is still unclear.

endif # TRANSPARENT_HUGEPAGE

simple helper to make the code a bit easier to read

config PAGE_MAPCOUNT def_bool !NO_PAGE_MAPCOUNT

The architecture supports pgtable leaves that is larger than PAGE_SIZE

config PGTABLE_HAS_HUGE_LEAVES def_bool TRANSPARENT_HUGEPAGE || HUGETLB_PAGE

TODO: Allow to be enabled without THP

config ARCH_SUPPORTS_HUGE_PFNMAP def_bool n depends on TRANSPARENT_HUGEPAGE

config ARCH_SUPPORTS_PMD_PFNMAP def_bool y depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE

config ARCH_SUPPORTS_PUD_PFNMAP def_bool y depends on ARCH_SUPPORTS_HUGE_PFNMAP && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD

UP and nommu archs use km based percpu allocator

config NEED_PER_CPU_KM depends on !SMP || !MMU bool default y

config NEED_PER_CPU_EMBED_FIRST_CHUNK bool

config NEED_PER_CPU_PAGE_FIRST_CHUNK bool

config USE_PERCPU_NUMA_NODE_ID bool

config HAVE_SETUP_PER_CPU_AREA bool

config CMA bool "Contiguous Memory Allocator" depends on 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_DEBUGFS bool "CMA debugfs interface" depends on CMA && DEBUG_FS help Turns on the DebugFS interface for CMA.

config CMA_SYSFS bool "CMA information through sysfs interface" depends on CMA && SYSFS help This option exposes some sysfs attributes to get information from CMA.

config CMA_AREAS int "Maximum count of the CMA areas" depends on CMA default 20 if NUMA default 8 help CMA allows to create CMA areas for particular purpose, mainly, used as device private area. This parameter sets the maximum number of CMA area in the system.

  If unsure, leave the default value "8" in UMA and "20" in NUMA.

Select this config option from the architecture Kconfig, if available, to set

the max page order for physically contiguous allocations.

config ARCH_FORCE_MAX_ORDER int

When ARCH_FORCE_MAX_ORDER is not defined,

the default page block order is MAX_PAGE_ORDER (10) as per

include/linux/mmzone.h.

config PAGE_BLOCK_ORDER int "Page Block Order" range 1 10 if ARCH_FORCE_MAX_ORDER = 0 default 10 if ARCH_FORCE_MAX_ORDER = 0 range 1 ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER != 0 default ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER != 0 help The page block order refers to the power of two number of pages that are physically contiguous and can have a migrate type associated to them. The maximum size of the page block order is limited by ARCH_FORCE_MAX_ORDER.

  This config allows overriding the default page block order when the
  page block order is required to be smaller than ARCH_FORCE_MAX_ORDER
  or MAX_PAGE_ORDER.

  Reducing pageblock order can negatively impact THP generation
  success rate. If your workloads uses THP heavily, please use this
  option with caution.

  Don't change if unsure.

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/admin-guide/mm/soft-dirty.rst for more details.

config GENERIC_EARLY_IOREMAP bool

config STACK_MAX_DEFAULT_SIZE_MB int "Default maximum user stack size for 32-bit processes (MB)" default 100 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 arch) when the RLIMIT_STACK hard limit is unlimited.

  A sane initial value is 100 MB.

config DEFERRED_STRUCT_PAGE_INIT bool "Defer initialisation of struct pages to kthreads" depends on SPARSEMEM depends on !NEED_PER_CPU_KM depends on 64BIT depends on !KMSAN select PADATA help Ordinarily all struct pages are initialised during early boot in a single thread. On very large machines this can take a considerable amount of time. If this option is set, large machines will bring up a subset of memmap at boot and then initialise the rest in parallel. This has a potential performance impact on tasks running early in the lifetime of the system until these kthreads finish the initialisation.

config PAGE_IDLE_FLAG bool select PAGE_EXTENSION if !64BIT help This adds PG_idle and PG_young flags to 'struct page'. PTE Accessed bit writers can set the state of the bit in the flags so that PTE Accessed bit readers may avoid disturbance.

config IDLE_PAGE_TRACKING bool "Enable idle page tracking" depends on SYSFS && MMU select PAGE_IDLE_FLAG help This feature allows to estimate the amount of user pages that have not been touched during a given period of time. This information can be useful to tune memory cgroup limits and/or for job placement within a compute cluster.

  See Documentation/admin-guide/mm/idle_page_tracking.rst for
  more details.

Architectures which implement cpu_dcache_is_aliasing() to query

whether the data caches are aliased (VIVT or VIPT with dcache

aliasing) need to select this.

config ARCH_HAS_CPU_CACHE_ALIASING bool

config ARCH_HAS_CACHE_LINE_SIZE bool

config ARCH_HAS_CURRENT_STACK_POINTER bool help In support of HARDENED_USERCOPY performing stack variable lifetime checking, an architecture-agnostic way to find the stack pointer is needed. Once an architecture defines an unsigned long global register alias named "current_stack_pointer", this config can be selected.

config ARCH_HAS_PTE_DEVMAP bool

config ARCH_HAS_ZONE_DMA_SET bool

config ZONE_DMA bool "Support DMA zone" if ARCH_HAS_ZONE_DMA_SET default y if ARM64 || X86

config ZONE_DMA32 bool "Support DMA32 zone" if ARCH_HAS_ZONE_DMA_SET depends on !X86_32 default y if ARM64

config ZONE_DEVICE bool "Device memory (pmem, HMM, etc...) hotplug support" depends on MEMORY_HOTPLUG depends on MEMORY_HOTREMOVE depends on SPARSEMEM_VMEMMAP depends on ARCH_HAS_PTE_DEVMAP select XARRAY_MULTI

help
  Device memory hotplug support allows for establishing pmem,
  or other device driver discovered memory regions, in the
  memmap. This allows pfn_to_page() lookups of otherwise
  "device-physical" addresses which is needed for using a DAX
  mapping in an O_DIRECT operation, among other things.

  If FS_DAX is enabled, then say Y.

Helpers to mirror range of the CPU page tables of a process into device page

tables.

config HMM_MIRROR bool depends on MMU

config GET_FREE_REGION bool

config DEVICE_PRIVATE bool "Unaddressable device memory (GPU memory, ...)" depends on ZONE_DEVICE select GET_FREE_REGION

help
  Allows creation of struct pages to represent unaddressable device
  memory; i.e., memory that is only accessible from the device (or
  group of devices). You likely also want to select HMM_MIRROR.

config VMAP_PFN bool

config ARCH_USES_HIGH_VMA_FLAGS bool config ARCH_HAS_PKEYS bool

config ARCH_USES_PG_ARCH_2 bool config ARCH_USES_PG_ARCH_3 bool

config VM_EVENT_COUNTERS default y bool "Enable VM event counters for /proc/vmstat" if EXPERT help VM event counters are needed for event counts to be shown. This option allows the disabling of the VM event counters on EXPERT systems. /proc/vmstat will only show page counts if VM event counters are disabled.

config PERCPU_STATS bool "Collect percpu memory statistics" help This feature collects and exposes statistics via debugfs. The information includes global and per chunk statistics, which can be used to help understand percpu memory usage.

config GUP_TEST bool "Enable infrastructure for get_user_pages()-related unit tests" depends on DEBUG_FS help Provides /sys/kernel/debug/gup_test, which in turn provides a way to make ioctl calls that can launch kernel-based unit tests for the get_user_pages*() and pin_user_pages*() family of API calls.

  These tests include benchmark testing of the _fast variants of
  get_user_pages*() and pin_user_pages*(), as well as smoke tests of
  the non-_fast variants.

  There is also a sub-test that allows running dump_page() on any
  of up to eight pages (selected by command line args) within the
  range of user-space addresses. These pages are either pinned via
  pin_user_pages*(), or pinned via get_user_pages*(), as specified
  by other command line arguments.

  See tools/testing/selftests/mm/gup_test.c

comment "GUP_TEST needs to have DEBUG_FS enabled" depends on !GUP_TEST && !DEBUG_FS

config GUP_GET_PXX_LOW_HIGH bool

config DMAPOOL_TEST tristate "Enable a module to run time tests on dma_pool" depends on HAS_DMA help Provides a test module that will allocate and free many blocks of various sizes and report how long it takes. This is intended to provide a consistent way to measure how changes to the dma_pool_alloc/free routines affect performance.

config ARCH_HAS_PTE_SPECIAL bool

config MAPPING_DIRTY_HELPERS bool

config KMAP_LOCAL bool

config KMAP_LOCAL_NON_LINEAR_PTE_ARRAY bool

struct io_mapping based helper. Selected by drivers that need them

config IO_MAPPING bool

config MEMFD_CREATE bool "Enable memfd_create() system call" if EXPERT

config SECRETMEM default y bool "Enable memfd_secret() system call" if EXPERT depends on ARCH_HAS_SET_DIRECT_MAP help Enable the memfd_secret() system call with the ability to create memory areas visible only in the context of the owning process and not mapped to other processes and other kernel page tables.

config ANON_VMA_NAME bool "Anonymous VMA name support" depends on PROC_FS && ADVISE_SYSCALLS && MMU

help
  Allow naming anonymous virtual memory areas.

  This feature allows assigning names to virtual memory areas. Assigned
  names can be later retrieved from /proc/pid/maps and /proc/pid/smaps
  and help identifying individual anonymous memory areas.
  Assigning a name to anonymous virtual memory area might prevent that
  area from being merged with adjacent virtual memory areas due to the
  difference in their name.

config HAVE_ARCH_USERFAULTFD_WP bool help Arch has userfaultfd write protection support

config HAVE_ARCH_USERFAULTFD_MINOR bool help Arch has userfaultfd minor fault support

menuconfig USERFAULTFD bool "Enable userfaultfd() system call" depends on MMU help Enable the userfaultfd() system call that allows to intercept and handle page faults in userland.

if USERFAULTFD config PTE_MARKER_UFFD_WP bool "Userfaultfd write protection support for shmem/hugetlbfs" default y depends on HAVE_ARCH_USERFAULTFD_WP

help
  Allows to create marker PTEs for userfaultfd write protection
  purposes.  It is required to enable userfaultfd write protection on
  file-backed memory types like shmem and hugetlbfs.

endif # USERFAULTFD

multi-gen LRU {

config LRU_GEN bool "Multi-Gen LRU" depends on MMU # make sure folio->flags has enough spare bits depends on 64BIT || !SPARSEMEM || SPARSEMEM_VMEMMAP help A high performance LRU implementation to overcommit memory. See Documentation/admin-guide/mm/multigen_lru.rst for details.

config LRU_GEN_ENABLED bool "Enable by default" depends on LRU_GEN help This option enables the multi-gen LRU by default.

config LRU_GEN_STATS bool "Full stats for debugging" depends on LRU_GEN help Do not enable this option unless you plan to look at historical stats from evicted generations for debugging purpose.

  This option has a per-memcg and per-node memory overhead.

config LRU_GEN_WALKS_MMU def_bool y depends on LRU_GEN && ARCH_HAS_HW_PTE_YOUNG

}

config ARCH_SUPPORTS_PER_VMA_LOCK def_bool n

config PER_VMA_LOCK def_bool y depends on ARCH_SUPPORTS_PER_VMA_LOCK && MMU && SMP help Allow per-vma locking during page fault handling.

  This feature allows locking each virtual memory area separately when
  handling page faults instead of taking mmap_lock.

config LOCK_MM_AND_FIND_VMA bool depends on !STACK_GROWSUP

config IOMMU_MM_DATA bool

config EXECMEM bool

config NUMA_MEMBLKS bool

config NUMA_EMU bool "NUMA emulation" depends on NUMA_MEMBLKS depends on X86 || GENERIC_ARCH_NUMA help Enable NUMA emulation. A flat machine will be split into virtual nodes when booted with "numa=fake=N", where N is the number of nodes. This is only useful for debugging.

config ARCH_HAS_USER_SHADOW_STACK bool help The architecture has hardware support for userspace shadow call stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss).

config ARCH_SUPPORTS_PT_RECLAIM def_bool n

config PT_RECLAIM bool "reclaim empty user page table pages" default y depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP select MMU_GATHER_RCU_TABLE_FREE help Try to reclaim empty user page table pages in paths other than munmap and exit_mmap path.

  Note: now only empty user PTE page table pages will be reclaimed.

source "mm/damon/Kconfig"

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