# 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
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 ZSMALLOC
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 ""
config ZSMALLOC
tristate
menu "Zsmalloc allocator options"
depends on ZSMALLOC
comment "Zsmalloc is a common backend allocator for zswap & zram"
config ZSMALLOC_STAT
bool "Export zsmalloc statistics"
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
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.
endmenu
menu "Slab allocator options"
config SLUB
def_bool y
select IRQ_WORK
config KVFREE_RCU_BATCHED
def_bool y
depends on !SLUB_TINY && !TINY_RCU
depends on !RCU_STRICT_GRACE_PERIOD
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 KMALLOC_PARTITION_CACHES
depends on !SLUB_TINY
bool "Partitioned slab caches for normal kmalloc"
default RANDOM_KMALLOC_CACHES
help
A hardening feature that creates multiple isolated copies of slab
caches for normal kmalloc allocations. This makes it more difficult
to exploit memory-safety vulnerabilities by attacking vulnerable
co-located memory objects. Several modes are provided.
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.
choice
prompt "Partitioned slab cache mode"
depends on KMALLOC_PARTITION_CACHES
default KMALLOC_PARTITION_TYPED if CC_HAS_ALLOC_TOKEN
default KMALLOC_PARTITION_RANDOM
help
Selects the slab cache partitioning mode.
config KMALLOC_PARTITION_RANDOM
bool "Randomize slab caches for normal kmalloc"
help
Randomly pick a slab cache based on code address and a per-boot
random seed.
This makes it harder for attackers to predict object co-location.
The placement is random: while attackers don't know which kmalloc
cache an object will be allocated from, they might circumvent
the randomization by retrying attacks across multiple machines until
the target objects are co-located.
config KMALLOC_PARTITION_TYPED
bool "Type based slab cache selection for normal kmalloc"
depends on CC_HAS_ALLOC_TOKEN
help
Rely on Clang's allocation tokens to choose a slab cache, where token
IDs are derived from the allocated type.
Unlike KMALLOC_PARTITION_RANDOM, cache assignment is deterministic based
on type, which guarantees that objects of certain types are not
placed in the same cache. This effectively mitigates certain classes
of exploits that probabilistic defenses like KMALLOC_PARTITION_RANDOM
only make harder but not impossible. However, this also means the
cache assignment is predictable.
Clang's default token ID calculation returns a bounded hash with
disjoint ranges for pointer-containing and pointerless objects: when
used as the slab cache index, this prevents buffer overflows on
primitive buffers from directly corrupting pointer-containing
objects.
The current effectiveness of Clang's type inference can be judged by
-Rpass=alloc-token, which provides diagnostics where (after dead-code
elimination) type inference failed.
Requires Clang 22 or later.
endchoice
config RANDOM_KMALLOC_CACHES
bool
transitional
help
Transitional config for migration to KMALLOC_PARTITION_CACHES.
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 !NUMA
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 !NUMA
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
def_bool y
depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
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
config ARCH_ENABLE_MEMORY_HOTPLUG
bool
# eventually, we can have this option just 'select SPARSEMEM'
menuconfig MEMORY_HOTPLUG
bool "Memory hotplug"
select MEMORY_ISOLATION
depends on SPARSEMEM_VMEMMAP
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 MIGRATION
config MHP_MEMMAP_ON_MEMORY
def_bool y
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
depends on !UML
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 BALLOON
bool
#
# support for memory balloon page migration
config BALLOON_MIGRATION
bool "Allow for balloon memory migration"
default y
depends on MIGRATION && BALLOON
help
Allow for migration of pages inflated in a memory balloon such that
they can be allocated from memory areas only available for movable
allocations (e.g., ZONE_MOVABLE, CMA) and such that they can be
migrated for memory defragmentation purposes by memory compaction.
#
# 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.
config NUMA_MIGRATION
bool "NUMA page migration"
default y
depends on NUMA && MMU
select MIGRATION
help
Support the migration of pages to other NUMA nodes, available to
user space through interfaces like migrate_pages(), move_pages(),
and mbind(). Selecting this option also enables support for page
demotion for memory tiering.
config MIGRATION
bool
depends on MMU
config DEVICE_MIGRATION
def_bool MIGRATION && ZONE_DEVICE
config ARCH_ENABLE_HUGEPAGE_MIGRATION
bool
config ARCH_HAS_PMD_SOFTLEAVES
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 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 INTERVAL_TREE
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 PERSISTENT_HUGE_ZERO_FOLIO
bool "Allocate a PMD sized folio for zeroing"
depends on TRANSPARENT_HUGEPAGE
help
Enable this option to reduce the runtime refcounting overhead
of the huge zero folio and expand the places in the kernel
that can use huge zero folios. For instance, block I/O benefits
from access to large folios for zeroing memory.
With this option enabled, the huge zero folio is allocated
once and never freed. One full huge page's worth of memory shall
be used.
Say Y if your system has lots of memory. Say N if you are
memory constrained.
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"
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
choice
prompt "Shmem hugepage allocation defaults"
default TRANSPARENT_HUGEPAGE_SHMEM_HUGE_NEVER
help
Selects the hugepage allocation policy defaults for
the internal shmem mount.
The selection made here can be overridden by using the kernel
command line 'transparent_hugepage_shmem=' option.
config TRANSPARENT_HUGEPAGE_SHMEM_HUGE_NEVER
bool "never"
help
Disable hugepage allocation for shmem mount by default. It can
still be enabled with the kernel command line
'transparent_hugepage_shmem=' option or at runtime via sysfs
knob. Note that madvise(MADV_COLLAPSE) can still cause
transparent huge pages to be obtained even if this mode is
specified.
config TRANSPARENT_HUGEPAGE_SHMEM_HUGE_ALWAYS
bool "always"
help
Always attempt to allocate hugepage for shmem mount, can
increase the memory footprint of applications without a
guaranteed benefit but it will work automatically for all
applications.
config TRANSPARENT_HUGEPAGE_SHMEM_HUGE_WITHIN_SIZE
bool "within_size"
help
Enable hugepage allocation for shmem mount if the allocation
will be fully within the i_size. This configuration also takes
into account any madvise(MADV_HUGEPAGE) hints that may be
provided by the applications.
config TRANSPARENT_HUGEPAGE_SHMEM_HUGE_ADVISE
bool "advise"
help
Enable hugepage allocation for the shmem mount exclusively when
applications supply the madvise(MADV_HUGEPAGE) hint.
This ensures that hugepages are used only in response to explicit
requests from applications.
endchoice
choice
prompt "Tmpfs hugepage allocation defaults"
default TRANSPARENT_HUGEPAGE_TMPFS_HUGE_NEVER
help
Selects the hugepage allocation policy defaults for
the tmpfs mount.
The selection made here can be overridden by using the kernel
command line 'transparent_hugepage_tmpfs=' option.
config TRANSPARENT_HUGEPAGE_TMPFS_HUGE_NEVER
bool "never"
help
Disable hugepage allocation for tmpfs mount by default. It can
still be enabled with the kernel command line
'transparent_hugepage_tmpfs=' option. Note that
madvise(MADV_COLLAPSE) can still cause transparent huge pages
to be obtained even if this mode is specified.
config TRANSPARENT_HUGEPAGE_TMPFS_HUGE_ALWAYS
bool "always"
help
Always attempt to allocate hugepage for tmpfs mount, can
increase the memory footprint of applications without a
guaranteed benefit but it will work automatically for all
applications.
config TRANSPARENT_HUGEPAGE_TMPFS_HUGE_WITHIN_SIZE
bool "within_size"
help
Enable hugepage allocation for tmpfs mount if the allocation
will be fully within the i_size. This configuration also takes
into account any madvise(MADV_HUGEPAGE) hints that may be
provided by the applications.
config TRANSPARENT_HUGEPAGE_TMPFS_HUGE_ADVISE
bool "advise"
help
Enable hugepage allocation for the tmpfs mount exclusively when
applications supply the madvise(MADV_HUGEPAGE) hint.
This ensures that hugepages are used only in response to explicit
requests from applications.
endchoice
config THP_SWAP
def_bool y
depends on 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 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
#
# We can end up creating gigantic folio.
#
config HAVE_GIGANTIC_FOLIOS
def_bool (HUGETLB_PAGE && ARCH_HAS_GIGANTIC_PAGE) || \
(ZONE_DEVICE && HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
config ASYNC_KERNEL_PGTABLE_FREE
def_bool n
# 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
#
# Architectures that always use weak definitions for percpu
# variables in modules should set this.
#
config ARCH_MODULE_NEEDS_WEAK_PER_CPU
bool
#
# 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_MAX_ORDER
int "Page Block Order Upper Limit"
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 at least limited by
ARCH_FORCE_MAX_ORDER/MAX_PAGE_ORDER.
This config adds a new upper limit of default page block
order when the page block order is required to be smaller than
ARCH_FORCE_MAX_ORDER/MAX_PAGE_ORDER or other limits
(see include/linux/pageblock-flags.h for details).
Reducing pageblock order can negatively impact THP generation
success rate. If your workloads use 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_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_HOTREMOVE
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 DAX, PCI_P2PDMA, and
DEVICE_PRIVATE features among others.
Enabling this option will reduce the entropy of x86 KASLR memory
regions. For example - on a 46 bit system, the entropy goes down
from 16 bits to 15 bits. The actual reduction in entropy depends
on the physical address bits, on processor features, kernel config
(5 level page table) and physical memory present on the system.
#
# Helpers to mirror range of the CPU page tables of a process into device page
# tables.
#
config HMM_MIRROR
bool
depends on MMU
select MMU_NOTIFIER
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
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
config USERFAULTFD_RWP
def_bool y
depends on 64BIT && ARCH_HAS_PTE_PROTNONE && HAVE_ARCH_USERFAULTFD_WP
help
Userfaultfd read-write protection (UFFDIO_RWPROTECT) delivers a
userfaultfd notification on every access -- read or write -- to a
protected range, letting userspace observe the working set of a
process.
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.
config PTE_MARKER_UFFD_WP
bool "Userfaultfd write protection support for shmem/hugetlbfs"
default y
depends on USERFAULTFD && 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.
# 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 GENERIC_ARCH_NUMA
bool
select NUMA_MEMBLKS
help
Enable support for generic NUMA implementation. Currently, RISC-V
and ARM64 use it.
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 HAVE_ARCH_TLB_REMOVE_TABLE
def_bool n
config PT_RECLAIM
def_bool y
depends on MMU_GATHER_RCU_TABLE_FREE && !HAVE_ARCH_TLB_REMOVE_TABLE
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.
config FIND_NORMAL_PAGE
def_bool n
config ARCH_HAS_LAZY_MMU_MODE
bool
help
The architecture uses the lazy MMU mode. This allows changes to
MMU-related architectural state to be deferred until the mode is
exited. See <linux/pgtable.h> for details.
config LAZY_MMU_MODE_KUNIT_TEST
tristate "KUnit tests for the lazy MMU mode" if !KUNIT_ALL_TESTS
depends on ARCH_HAS_LAZY_MMU_MODE
depends on KUNIT
default KUNIT_ALL_TESTS
help
Enable this option to check that the lazy MMU mode interface behaves
as expected. Only tests for the generic interface are included (not
architecture-specific behaviours).
If unsure, say N.
source "mm/damon/Kconfig"
endmenu
