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config SELECT_MEMORY_MODEL
def_bool y
depends on EXPERIMENTAL || 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 an 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

# eventually, we can have this option just 'select SPARSEMEM'
config MEMORY_HOTPLUG
bool "Allow for memory hot-add"
select MEMORY_ISOLATION
depends on SPARSEMEM || X86_64_ACPI_NUMA
depends on HOTPLUG && 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"
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 ARM && !CPU_CACHE_VIPT
default "999999" if PARISC && !PA20
default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
default "4"

#
# 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
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
def_bool y
depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)

config NR_QUICK
int
depends on QUICKLIST
default "2" if AVR32
default "1"

config VIRT_TO_BUS
def_bool y
depends on !ARCH_NO_VIRT_TO_BUS

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.
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