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 FRONTSWAP
	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.

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_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
	bool "z3fold"
	select Z3FOLD
	help
	  Use the z3fold allocator as the default allocator.

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
       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
	tristate "3:1 compression allocator (z3fold)"
	depends on ZSWAP
	help
	  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 ZSMALLOC
	tristate
	prompt "N:1 compression allocator (zsmalloc)" if ZSWAP
	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.

menu "SLAB allocator options"

choice
	prompt "Choose SLAB allocator"
	default SLUB
	help
	   This option allows to select a slab allocator.

config SLAB
	bool "SLAB"
	depends on !PREEMPT_RT
	select HAVE_HARDENED_USERCOPY_ALLOCATOR
	help
	  The regular slab allocator that is established and known to work
	  well in all environments. It organizes cache hot objects in
	  per cpu and per node queues.

config SLUB
	bool "SLUB (Unqueued Allocator)"
	select HAVE_HARDENED_USERCOPY_ALLOCATOR
	help
	   SLUB is a slab allocator that minimizes cache line usage
	   instead of managing queues of cached objects (SLAB approach).
	   Per cpu caching is realized using slabs of objects instead
	   of queues of objects. SLUB can use memory efficiently
	   and has enhanced diagnostics. SLUB is the default choice for
	   a slab allocator.

config SLOB_DEPRECATED
	depends on EXPERT
	bool "SLOB (Simple Allocator - DEPRECATED)"
	depends on !PREEMPT_RT
	help
	   Deprecated and scheduled for removal in a few cycles. SLUB
	   recommended as replacement. CONFIG_SLUB_TINY can be considered
	   on systems with 16MB or less RAM.

	   If you need SLOB to stay, please contact linux-mm@kvack.org and
	   people listed in the SLAB ALLOCATOR section of MAINTAINERS file,
	   with your use case.

	   SLOB replaces the stock allocator with a drastically simpler
	   allocator. SLOB is generally more space efficient but
	   does not perform as well on large systems.

endchoice

config SLOB
	bool
	default y
	depends on SLOB_DEPRECATED

config SLUB_TINY
	bool "Configure SLUB for minimal memory footprint"
	depends on SLUB && EXPERT
	select SLAB_MERGE_DEFAULT
	help
	   Configures the SLUB 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
	depends on SLAB || SLUB
	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 SLAB || (SLUB && !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