config SELECT_MEMORY_MODEL
def_bool y
depends on ARCH_SELECT_MEMORY_MODEL
choice
prompt "Memory model"
depends on SELECT_MEMORY_MODEL
default DISCONTIGMEM_MANUAL if ARCH_DISCONTIGMEM_DEFAULT
default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
default FLATMEM_MANUAL
config FLATMEM_MANUAL
bool "Flat Memory"
depends on !(ARCH_DISCONTIGMEM_ENABLE || ARCH_SPARSEMEM_ENABLE) || ARCH_FLATMEM_ENABLE
help
This option allows you to change some of the ways that
Linux manages its memory internally. Most users will
only have one option here: FLATMEM. This is normal
and a correct option.
Some users of more advanced features like NUMA and
memory hotplug may have different options here.
DISCONTIGMEM is a more mature, better tested system,
but is incompatible with memory hotplug and may suffer
decreased performance over SPARSEMEM. If unsure between
"Sparse Memory" and "Discontiguous Memory", choose
"Discontiguous Memory".
If unsure, choose this option (Flat Memory) over any other.
config DISCONTIGMEM_MANUAL
bool "Discontiguous Memory"
depends on ARCH_DISCONTIGMEM_ENABLE
help
This option provides enhanced support for discontiguous
memory systems, over FLATMEM. These systems have holes
in their physical address spaces, and this option provides
more efficient handling of these holes. However, the vast
majority of hardware has quite flat address spaces, and
can have degraded performance from the extra overhead that
this option imposes.
Many NUMA configurations will have this as the only option.
If unsure, choose "Flat Memory" over this option.
config SPARSEMEM_MANUAL
bool "Sparse Memory"
depends on ARCH_SPARSEMEM_ENABLE
help
This will be the only option for some systems, including
memory hotplug systems. This is normal.
For many other systems, this will be an alternative to
"Discontiguous Memory". This option provides some potential
performance benefits, along with decreased code complexity,
but it is newer, and more experimental.
If unsure, choose "Discontiguous Memory" or "Flat Memory"
over this option.
endchoice
config DISCONTIGMEM
def_bool y
depends on (!SELECT_MEMORY_MODEL && ARCH_DISCONTIGMEM_ENABLE) || DISCONTIGMEM_MANUAL
config SPARSEMEM
def_bool y
depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL
config FLATMEM
def_bool y
depends on (!DISCONTIGMEM && !SPARSEMEM) || FLATMEM_MANUAL
config FLAT_NODE_MEM_MAP
def_bool y
depends on !SPARSEMEM
#
# Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's
# to represent different areas of memory. This variable allows
# those dependencies to exist individually.
#
config NEED_MULTIPLE_NODES
def_bool y
depends on DISCONTIGMEM || NUMA
config HAVE_MEMORY_PRESENT
def_bool y
depends on ARCH_HAVE_MEMORY_PRESENT || SPARSEMEM
#
# SPARSEMEM_EXTREME (which is the default) does some bootmem
# allocations when memory_present() is called. If this cannot
# be done on your architecture, select this option. However,
# statically allocating the mem_section[] array can potentially
# consume vast quantities of .bss, so be careful.
#
# This option will also potentially produce smaller runtime code
# with gcc 3.4 and later.
#
config SPARSEMEM_STATIC
bool
#
# Architecture platforms which require a two level mem_section in SPARSEMEM
# must select this option. This is usually for architecture platforms with
# an extremely sparse physical address space.
#
config SPARSEMEM_EXTREME
def_bool y
depends on SPARSEMEM && !SPARSEMEM_STATIC
config SPARSEMEM_VMEMMAP_ENABLE
bool
config SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
def_bool y
depends on SPARSEMEM && X86_64
config SPARSEMEM_VMEMMAP
bool "Sparse Memory virtual memmap"
depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
default y
help
SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
pfn_to_page and page_to_pfn operations. This is the most
efficient option when sufficient kernel resources are available.
config HAVE_MEMBLOCK
boolean
config HAVE_MEMBLOCK_NODE_MAP
boolean
config ARCH_DISCARD_MEMBLOCK
boolean
config NO_BOOTMEM
boolean
config MEMORY_ISOLATION
boolean
config MOVABLE_NODE
boolean "Enable to assign a node which has only movable memory"
depends on HAVE_MEMBLOCK
depends on NO_BOOTMEM
depends on X86_64
depends on NUMA
default n
help
Allow a node to have only movable memory. Pages used by the kernel,
such as direct mapping pages cannot be migrated. So the corresponding
memory device cannot be hotplugged. This option allows the following
two things:
- When the system is booting, node full of hotpluggable memory can
be arranged to have only movable memory so that the whole node can
be hot-removed. (need movable_node boot option specified).
- After the system is up, the option allows users to online all the
memory of a node as movable memory so that the whole node can be
hot-removed.
Users who don't use the memory hotplug feature are fine with this
option on since they don't specify movable_node boot option or they
don't online memory as movable.
Say Y here if you want to hotplug a whole node.
Say N here if you want kernel to use memory on all nodes evenly.
#
# Only be set on architectures that have completely implemented memory hotplug
# feature. If you are not sure, don't touch it.
#
config HAVE_BOOTMEM_INFO_NODE
def_bool n
# eventually, we can have this option just 'select SPARSEMEM'
config MEMORY_HOTPLUG
bool "Allow for memory hot-add"
depends on SPARSEMEM || X86_64_ACPI_NUMA
depends on ARCH_ENABLE_MEMORY_HOTPLUG
depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
config MEMORY_HOTPLUG_SPARSE
def_bool y
depends on SPARSEMEM && MEMORY_HOTPLUG
config MEMORY_HOTREMOVE
bool "Allow for memory hot remove"
select MEMORY_ISOLATION
select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
depends on MIGRATION
#
# If we have space for more page flags then we can enable additional
# optimizations and functionality.
#
# Regular Sparsemem takes page flag bits for the sectionid if it does not
# use a virtual memmap. Disable extended page flags for 32 bit platforms
# that require the use of a sectionid in the page flags.
#
config PAGEFLAGS_EXTENDED
def_bool y
depends on 64BIT || SPARSEMEM_VMEMMAP || !SPARSEMEM
# Heavily threaded applications may benefit from splitting the mm-wide
# page_table_lock, so that faults on different parts of the user address
# space can be handled with less contention: split it at this NR_CPUS.
# Default to 4 for wider testing, though 8 might be more appropriate.
# ARM's adjust_pte (unused if VIPT) depends on mm-wide page_table_lock.
# PA-RISC 7xxx's spinlock_t would enlarge struct page from 32 to 44 bytes.
# DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
#
config SPLIT_PTLOCK_CPUS
int
default "999999" if !MMU
default "999999" if ARM && !CPU_CACHE_VIPT
default "999999" if PARISC && !PA20
default "4"
config ARCH_ENABLE_SPLIT_PMD_PTLOCK
boolean
#
# support for memory balloon compaction
config BALLOON_COMPACTION
bool "Allow for balloon memory compaction/migration"
def_bool y
depends on COMPACTION && VIRTIO_BALLOON
help
Memory fragmentation introduced by ballooning might reduce
significantly the number of 2MB contiguous memory blocks that can be
used within a guest, thus imposing performance penalties associated
with the reduced number of transparent huge pages that could be used
by the guest workload. Allowing the compaction & migration for memory
pages enlisted as being part of memory balloon devices avoids the
scenario aforementioned and helps improving memory defragmentation.
#
# support for memory compaction
config COMPACTION
bool "Allow for memory compaction"
def_bool y
select MIGRATION
depends on MMU
help
Allows the compaction of memory for the allocation of huge pages.
#
# support for page migration
#
config MIGRATION
bool "Page migration"
def_bool y
depends on (NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
help
Allows the migration of the physical location of pages of processes
while the virtual addresses are not changed. This is useful in
two situations. The first is on NUMA systems to put pages nearer
to the processors accessing. The second is when allocating huge
pages as migration can relocate pages to satisfy a huge page
allocation instead of reclaiming.
config PHYS_ADDR_T_64BIT
def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
config ZONE_DMA_FLAG
int
default "0" if !ZONE_DMA
default "1"
config BOUNCE
bool "Enable bounce buffers"
default y
depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
help
Enable bounce buffers for devices that cannot access
the full range of memory available to the CPU. Enabled
by default when ZONE_DMA or HIGHMEM is selected, but you
may say n to override this.
# On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
# have more than 4GB of memory, but we don't currently use the IOTLB to present
# a 32-bit address to OHCI. So we need to use a bounce pool instead.
#
# We also use the bounce pool to provide stable page writes for jbd. jbd
# initiates buffer writeback without locking the page or setting PG_writeback,
# and fixing that behavior (a second time; jbd2 doesn't have this problem) is
# a major rework effort. Instead, use the bounce buffer to snapshot pages
# (until jbd goes away). The only jbd user is ext3.
config NEED_BOUNCE_POOL
bool
default y if (TILE && USB_OHCI_HCD) || (BLK_DEV_INTEGRITY && JBD)
config NR_QUICK
int
depends on QUICKLIST
default "2" if AVR32
default "1"
config VIRT_TO_BUS
bool
help
An architecture should select this if it implements the
deprecated interface virt_to_bus(). All new architectures
should probably not select this.
config MMU_NOTIFIER
bool
config KSM
bool "Enable KSM for page merging"
depends on MMU
help
Enable Kernel Samepage Merging: KSM periodically scans those areas
of an application's address space that an app has advised may be
mergeable. When it finds pages of identical content, it replaces
the many instances by a single page with that content, so
saving memory until one or another app needs to modify the content.
Recommended for use with KVM, or with other duplicative applications.
See Documentation/vm/ksm.txt for more information: KSM is inactive
until a program has madvised that an area is MADV_MERGEABLE, and
root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
config DEFAULT_MMAP_MIN_ADDR
int "Low address space to protect from user allocation"
depends on MMU
default 4096
help
This is the portion of low virtual memory which should be protected
from userspace allocation. Keeping a user from writing to low pages
can help reduce the impact of kernel NULL pointer bugs.
For most ia64, ppc64 and x86 users with lots of address space
a value of 65536 is reasonable and should cause no problems.
On arm and other archs it should not be higher than 32768.
Programs which use vm86 functionality or have some need to map
this low address space will need CAP_SYS_RAWIO or disable this
protection by setting the value to 0.
This value can be changed after boot using the
/proc/sys/vm/mmap_min_addr tunable.
config ARCH_SUPPORTS_MEMORY_FAILURE
bool
config MEMORY_FAILURE
depends on MMU
depends on ARCH_SUPPORTS_MEMORY_FAILURE
bool "Enable recovery from hardware memory errors"
select MEMORY_ISOLATION
help
Enables code to recover from some memory failures on systems
with MCA recovery. This allows a system to continue running
even when some of its memory has uncorrected errors. This requires
special hardware support and typically ECC memory.
config HWPOISON_INJECT
tristate "HWPoison pages injector"
depends on MEMORY_FAILURE && DEBUG_KERNEL && PROC_FS
select PROC_PAGE_MONITOR
config NOMMU_INITIAL_TRIM_EXCESS
int "Turn on mmap() excess space trimming before booting"
depends on !MMU
default 1
help
The NOMMU mmap() frequently needs to allocate large contiguous chunks
of memory on which to store mappings, but it can only ask the system
allocator for chunks in 2^N*PAGE_SIZE amounts - which is frequently
more than it requires. To deal with this, mmap() is able to trim off
the excess and return it to the allocator.
If trimming is enabled, the excess is trimmed off and returned to the
system allocator, which can cause extra fragmentation, particularly
if there are a lot of transient processes.
If trimming is disabled, the excess is kept, but not used, which for
long-term mappings means that the space is wasted.
Trimming can be dynamically controlled through a sysctl option
(/proc/sys/vm/nr_trim_pages) which specifies the minimum number of
excess pages there must be before trimming should occur, or zero if
no trimming is to occur.
This option specifies the initial value of this option. The default
of 1 says that all excess pages should be trimmed.
See Documentation/nommu-mmap.txt for more information.
config TRANSPARENT_HUGEPAGE
bool "Transparent Hugepage Support"
depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
select COMPACTION
help
Transparent Hugepages allows the kernel to use huge pages and
huge tlb transparently to the applications whenever possible.
This feature can improve computing performance to certain
applications by speeding up page faults during memory
allocation, by reducing the number of tlb misses and by speeding
up the pagetable walking.
If memory constrained on embedded, you may want to say N.
choice
prompt "Transparent Hugepage Support sysfs defaults"
depends on TRANSPARENT_HUGEPAGE
default TRANSPARENT_HUGEPAGE_ALWAYS
help
Selects the sysfs defaults for Transparent Hugepage Support.
config TRANSPARENT_HUGEPAGE_ALWAYS
bool "always"
help
Enabling Transparent Hugepage always, can increase the
memory footprint of applications without a guaranteed
benefit but it will work automatically for all applications.
config TRANSPARENT_HUGEPAGE_MADVISE
bool "madvise"
help
Enabling Transparent Hugepage madvise, will only provide a
performance improvement benefit to the applications using
madvise(MADV_HUGEPAGE) but it won't risk to increase the
memory footprint of applications without a guaranteed
benefit.
endchoice
config CROSS_MEMORY_ATTACH
bool "Cross Memory Support"
depends on MMU
default y
help
Enabling this option adds the system calls process_vm_readv and
process_vm_writev which allow a process with the correct privileges
to directly read from or write to to another process's address space.
See the man page for more details.
#
# UP and nommu archs use km based percpu allocator
#
config NEED_PER_CPU_KM
depends on !SMP
bool
default y
config CLEANCACHE
bool "Enable cleancache driver to cache clean pages if tmem is present"
default n
help
Cleancache can be thought of as a page-granularity victim cache
for clean pages that the kernel's pageframe replacement algorithm
(PFRA) would like to keep around, but can't since there isn't enough
memory. So when the PFRA "evicts" a page, it first attempts to use
cleancache code to put the data contained in that page into
"transcendent memory", memory that is not directly accessible or
addressable by the kernel and is of unknown and possibly
time-varying size. And when a cleancache-enabled
filesystem wishes to access a page in a file on disk, it first
checks cleancache to see if it already contains it; if it does,
the page is copied into the kernel and a disk access is avoided.
When a transcendent memory driver is available (such as zcache or
Xen transcendent memory), a significant I/O reduction
may be achieved. When none is available, all cleancache calls
are reduced to a single pointer-compare-against-NULL resulting
in a negligible performance hit.
If unsure, say Y to enable cleancache
config FRONTSWAP
bool "Enable frontswap to cache swap pages if tmem is present"
depends on SWAP
default n
help
Frontswap is so named because it can be thought of as the opposite
of a "backing" store for a swap device. The data is stored into
"transcendent memory", memory that is not directly accessible or
addressable by the kernel and is of unknown and possibly
time-varying size. When space in transcendent memory is available,
a significant swap I/O reduction may be achieved. When none is
available, all frontswap calls are reduced to a single pointer-
compare-against-NULL resulting in a negligible performance hit
and swap data is stored as normal on the matching swap device.
If unsure, say Y to enable frontswap.
config CMA
bool "Contiguous Memory Allocator"
depends on HAVE_MEMBLOCK && MMU
select MIGRATION
select MEMORY_ISOLATION
help
This enables the Contiguous Memory Allocator which allows other
subsystems to allocate big physically-contiguous blocks of memory.
CMA reserves a region of memory and allows only movable pages to
be allocated from it. This way, the kernel can use the memory for
pagecache and when a subsystem requests for contiguous area, the
allocated pages are migrated away to serve the contiguous request.
If unsure, say "n".
config CMA_DEBUG
bool "CMA debug messages (DEVELOPMENT)"
depends on DEBUG_KERNEL && CMA
help
Turns on debug messages in CMA. This produces KERN_DEBUG
messages for every CMA call as well as various messages while
processing calls such as dma_alloc_from_contiguous().
This option does not affect warning and error messages.
config ZBUD
tristate
default n
help
A special purpose allocator for storing compressed pages.
It is designed to store up to two compressed pages per physical
page. While this design limits storage density, it has simple and
deterministic reclaim properties that make it preferable to a higher
density approach when reclaim will be used.
config ZSWAP
bool "Compressed cache for swap pages (EXPERIMENTAL)"
depends on FRONTSWAP && CRYPTO=y
select CRYPTO_LZO
select ZBUD
default n
help
A lightweight compressed cache for swap pages. It takes
pages that are in the process of being swapped out and attempts to
compress them into a dynamically allocated RAM-based memory pool.
This can result in a significant I/O reduction on swap device and,
in the case where decompressing from RAM is faster that swap device
reads, can also improve workload performance.
This is marked experimental because it is a new feature (as of
v3.11) that interacts heavily with memory reclaim. While these
interactions don't cause any known issues on simple memory setups,
they have not be fully explored on the large set of potential
configurations and workloads that exist.
config MEM_SOFT_DIRTY
bool "Track memory changes"
depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY && PROC_FS
select PROC_PAGE_MONITOR
help
This option enables memory changes tracking by introducing a
soft-dirty bit on pte-s. This bit it set when someone writes
into a page just as regular dirty bit, but unlike the latter
it can be cleared by hands.
See Documentation/vm/soft-dirty.txt for more details.
config ZSMALLOC
bool "Memory allocator for compressed pages"
depends on MMU
default n
help
zsmalloc is a slab-based memory allocator designed to store
compressed RAM pages. zsmalloc uses virtual memory mapping
in order to reduce fragmentation. However, this results in a
non-standard allocator interface where a handle, not a pointer, is
returned by an alloc(). This handle must be mapped in order to
access the allocated space.
config PGTABLE_MAPPING
bool "Use page table mapping to access object in zsmalloc"
depends on ZSMALLOC
help
By default, zsmalloc uses a copy-based object mapping method to
access allocations that span two pages. However, if a particular
architecture (ex, ARM) performs VM mapping faster than copying,
then you should select this. This causes zsmalloc to use page table
mapping rather than copying for object mapping.
You can check speed with zsmalloc benchmark:
https://github.com/spartacus06/zsmapbench
