path: root/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
	default ZSWAP_ZPOOL_DEFAULT_ZBUD
	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_ZBUD
	bool "zbud"
	select ZBUD
	help
	  Use the zbud allocator as the default allocator.

config ZSWAP_ZPOOL_DEFAULT_Z3FOLD_DEPRECATED
	bool "z3foldi (DEPRECATED)"
	select Z3FOLD_DEPRECATED
	help
	  Use the z3fold allocator as the default allocator.

	  Deprecated and scheduled for removal in a few cycles,
	  see CONFIG_Z3FOLD_DEPRECATED.

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 "zbud" if ZSWAP_ZPOOL_DEFAULT_ZBUD
       default "z3fold" if ZSWAP_ZPOOL_DEFAULT_Z3FOLD_DEPRECATED
       default "zsmalloc" if ZSWAP_ZPOOL_DEFAULT_ZSMALLOC
       default ""

config ZBUD
	tristate "2:1 compression allocator (zbud)"
	depends on ZSWAP
	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 Z3FOLD_DEPRECATED
	tristate "3:1 compression allocator (z3fold) (DEPRECATED)"
	depends on ZSWAP
	help
	  Deprecated and scheduled for removal in a few cycles. If you have
	  a good reason for using Z3FOLD over ZSMALLOC, please contact
	  linux-mm@kvack.org and the zswap maintainers.

	  A special purpose allocator for storing compressed pages.
	  It is designed to store up to three compressed pages per physical
	  page. It is a ZBUD derivative so the simplicity and determinism are
	  still there.

config Z3FOLD
	tristate
	default y if Z3FOLD_DEPRECATED=y
	default m if Z3FOLD_DEPRECATED=m
	depends on Z3FOLD_DEPRECATED

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 SLUB_TINY
	bool "Configure for minimal memory footprint"
	depends on EXPERT
	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.
#
# 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 HAVE_MEMBLOCK_PHYS_MAP
	bool