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Commit db0fb184 authored by Peter W Morreale's avatar Peter W Morreale Committed by Linus Torvalds
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Update of Documentation: vm.txt and proc.txt 

Update Documentation/sysctl/vm.txt and Documentation/filesystems/proc.txt.
 More specifically, the section on /proc/sys/vm in
Documentation/filesystems/proc.txt was removed and a link to
Documentation/sysctl/vm.txt added.

Most of the verbiage from proc.txt was simply moved in vm.txt, with new
addtional text for "swappiness" and "stat_interval".
Signed-off-by: default avatarPeter W Morreale <pmorreale@novell.com>
Acked-by: default avatarRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b5db0e38
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Documentation/filesystems/proc.txt
View file @ db0fb184
......@@ -1371,292 +1371,8 @@ auto_msgmni default value is 1.
2.4 /proc/sys/vm - The virtual memory subsystem
-----------------------------------------------
The files in this directory can be used to tune the operation of the virtual
memory (VM) subsystem of the Linux kernel.
vfs_cache_pressure
------------------
Controls the tendency of the kernel to reclaim the memory which is used for
caching of directory and inode objects.
At the default value of vfs_cache_pressure=100 the kernel will attempt to
reclaim dentries and inodes at a "fair" rate with respect to pagecache and
swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
causes the kernel to prefer to reclaim dentries and inodes.
dirty_background_bytes
----------------------
Contains the amount of dirty memory at which the pdflush background writeback
daemon will start writeback.
If dirty_background_bytes is written, dirty_background_ratio becomes a function
of its value (dirty_background_bytes / the amount of dirtyable system memory).
dirty_background_ratio
----------------------
Contains, as a percentage of the dirtyable system memory (free pages + mapped
pages + file cache, not including locked pages and HugePages), the number of
pages at which the pdflush background writeback daemon will start writing out
dirty data.
If dirty_background_ratio is written, dirty_background_bytes becomes a function
of its value (dirty_background_ratio * the amount of dirtyable system memory).
dirty_bytes
-----------
Contains the amount of dirty memory at which a process generating disk writes
will itself start writeback.
If dirty_bytes is written, dirty_ratio becomes a function of its value
(dirty_bytes / the amount of dirtyable system memory).
dirty_ratio
-----------
Contains, as a percentage of the dirtyable system memory (free pages + mapped
pages + file cache, not including locked pages and HugePages), the number of
pages at which a process which is generating disk writes will itself start
writing out dirty data.
If dirty_ratio is written, dirty_bytes becomes a function of its value
(dirty_ratio * the amount of dirtyable system memory).
dirty_writeback_centisecs
-------------------------
The pdflush writeback daemons will periodically wake up and write `old' data
out to disk. This tunable expresses the interval between those wakeups, in
100'ths of a second.
Setting this to zero disables periodic writeback altogether.
dirty_expire_centisecs
----------------------
This tunable is used to define when dirty data is old enough to be eligible
for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
Data which has been dirty in-memory for longer than this interval will be
written out next time a pdflush daemon wakes up.
highmem_is_dirtyable
--------------------
Only present if CONFIG_HIGHMEM is set.
This defaults to 0 (false), meaning that the ratios set above are calculated
as a percentage of lowmem only. This protects against excessive scanning
in page reclaim, swapping and general VM distress.
Setting this to 1 can be useful on 32 bit machines where you want to make
random changes within an MMAPed file that is larger than your available
lowmem without causing large quantities of random IO. Is is safe if the
behavior of all programs running on the machine is known and memory will
not be otherwise stressed.
legacy_va_layout
----------------
If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
will use the legacy (2.4) layout for all processes.
lowmem_reserve_ratio
---------------------
For some specialised workloads on highmem machines it is dangerous for
the kernel to allow process memory to be allocated from the "lowmem"
zone. This is because that memory could then be pinned via the mlock()
system call, or by unavailability of swapspace.
And on large highmem machines this lack of reclaimable lowmem memory
can be fatal.
So the Linux page allocator has a mechanism which prevents allocations
which _could_ use highmem from using too much lowmem. This means that
a certain amount of lowmem is defended from the possibility of being
captured into pinned user memory.
(The same argument applies to the old 16 megabyte ISA DMA region. This
mechanism will also defend that region from allocations which could use
highmem or lowmem).
The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
in defending these lower zones.
If you have a machine which uses highmem or ISA DMA and your
applications are using mlock(), or if you are running with no swap then
you probably should change the lowmem_reserve_ratio setting.
The lowmem_reserve_ratio is an array. You can see them by reading this file.
-
% cat /proc/sys/vm/lowmem_reserve_ratio
256 256 32
-
Note: # of this elements is one fewer than number of zones. Because the highest
zone's value is not necessary for following calculation.
But, these values are not used directly. The kernel calculates # of protection
pages for each zones from them. These are shown as array of protection pages
in /proc/zoneinfo like followings. (This is an example of x86-64 box).
Each zone has an array of protection pages like this.
-
Node 0, zone DMA
pages free 1355
min 3
low 3
high 4
:
:
numa_other 0
protection: (0, 2004, 2004, 2004)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pagesets
cpu: 0 pcp: 0
:
-
These protections are added to score to judge whether this zone should be used
for page allocation or should be reclaimed.
In this example, if normal pages (index=2) are required to this DMA zone and
pages_high is used for watermark, the kernel judges this zone should not be
used because pages_free(1355) is smaller than watermark + protection[2]
(4 + 2004 = 2008). If this protection value is 0, this zone would be used for
normal page requirement. If requirement is DMA zone(index=0), protection[0]
(=0) is used.
zone[i]'s protection[j] is calculated by following expression.
(i < j):
zone[i]->protection[j]
= (total sums of present_pages from zone[i+1] to zone[j] on the node)
/ lowmem_reserve_ratio[i];
(i = j):
(should not be protected. = 0;
(i > j):
(not necessary, but looks 0)
The default values of lowmem_reserve_ratio[i] are
256 (if zone[i] means DMA or DMA32 zone)
32 (others).
As above expression, they are reciprocal number of ratio.
256 means 1/256. # of protection pages becomes about "0.39%" of total present
pages of higher zones on the node.
If you would like to protect more pages, smaller values are effective.
The minimum value is 1 (1/1 -> 100%).
page-cluster
------------
page-cluster controls the number of pages which are written to swap in
a single attempt. The swap I/O size.
It is a logarithmic value - setting it to zero means "1 page", setting
it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
The default value is three (eight pages at a time). There may be some
small benefits in tuning this to a different value if your workload is
swap-intensive.
overcommit_memory
-----------------
Controls overcommit of system memory, possibly allowing processes
to allocate (but not use) more memory than is actually available.
0 - Heuristic overcommit handling. Obvious overcommits of
address space are refused. Used for a typical system. It
ensures a seriously wild allocation fails while allowing
overcommit to reduce swap usage. root is allowed to
allocate slightly more memory in this mode. This is the
default.
1 - Always overcommit. Appropriate for some scientific
applications.
2 - Don't overcommit. The total address space commit
for the system is not permitted to exceed swap plus a
configurable percentage (default is 50) of physical RAM.
Depending on the percentage you use, in most situations
this means a process will not be killed while attempting
to use already-allocated memory but will receive errors
on memory allocation as appropriate.
overcommit_ratio
----------------
Percentage of physical memory size to include in overcommit calculations
(see above.)
Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)
swapspace = total size of all swap areas
physmem = size of physical memory in system
nr_hugepages and hugetlb_shm_group
----------------------------------
nr_hugepages configures number of hugetlb page reserved for the system.
hugetlb_shm_group contains group id that is allowed to create SysV shared
memory segment using hugetlb page.
hugepages_treat_as_movable
--------------------------
This parameter is only useful when kernelcore= is specified at boot time to
create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages
are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero
value written to hugepages_treat_as_movable allows huge pages to be allocated
from ZONE_MOVABLE.
Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge
pages pool can easily grow or shrink within. Assuming that applications are
not running that mlock() a lot of memory, it is likely the huge pages pool
can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value
into nr_hugepages and triggering page reclaim.
laptop_mode
-----------
laptop_mode is a knob that controls "laptop mode". All the things that are
controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt.
block_dump
----------
block_dump enables block I/O debugging when set to a nonzero value. More
information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
swap_token_timeout
------------------
This file contains valid hold time of swap out protection token. The Linux
VM has token based thrashing control mechanism and uses the token to prevent
unnecessary page faults in thrashing situation. The unit of the value is
second. The value would be useful to tune thrashing behavior.
drop_caches
-----------
Writing to this will cause the kernel to drop clean caches, dentries and
inodes from memory, causing that memory to become free.
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation and dirty objects are not freeable, the
user should run `sync' first.
Please see: Documentation/sysctls/vm.txt for a description of these
entries.
2.5 /proc/sys/dev - Device specific parameters
......
Documentation/sysctl/vm.txt
View file @ db0fb184
Documentation for /proc/sys/vm/* kernel version 2.2.10
Documentation for /proc/sys/vm/* kernel version 2.6.29
(c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
(c) 2008 Peter W. Morreale <pmorreale@novell.com>
For general info and legal blurb, please look in README.
==============================================================
This file contains the documentation for the sysctl files in
/proc/sys/vm and is valid for Linux kernel version 2.2.
/proc/sys/vm and is valid for Linux kernel version 2.6.29.
The files in this directory can be used to tune the operation
of the virtual memory (VM) subsystem of the Linux kernel and
......@@ -16,83 +17,244 @@ Default values and initialization routines for most of these
files can be found in mm/swap.c.
Currently, these files are in /proc/sys/vm:
- overcommit_memory
- page-cluster
- dirty_ratio
- block_dump
- dirty_background_bytes
- dirty_background_ratio
- dirty_bytes
- dirty_expire_centisecs
- dirty_ratio
- dirty_writeback_centisecs
- highmem_is_dirtyable (only if CONFIG_HIGHMEM set)
- drop_caches
- hugepages_treat_as_movable
- hugetlb_shm_group
- laptop_mode
- legacy_va_layout
- lowmem_reserve_ratio
- max_map_count
- min_free_kbytes
- laptop_mode
- block_dump
- drop-caches
- zone_reclaim_mode
- min_unmapped_ratio
- min_slab_ratio
- panic_on_oom
- oom_dump_tasks
- oom_kill_allocating_task
- mmap_min_address
- numa_zonelist_order
- min_unmapped_ratio
- mmap_min_addr
- nr_hugepages
- nr_overcommit_hugepages
- nr_pdflush_threads
- nr_trim_pages (only if CONFIG_MMU=n)
- numa_zonelist_order
- oom_dump_tasks
- oom_kill_allocating_task
- overcommit_memory
- overcommit_ratio
- page-cluster
- panic_on_oom
- percpu_pagelist_fraction
- stat_interval
- swappiness
- vfs_cache_pressure
- zone_reclaim_mode
==============================================================
dirty_bytes, dirty_ratio, dirty_background_bytes,
dirty_background_ratio, dirty_expire_centisecs,
dirty_writeback_centisecs, highmem_is_dirtyable,
vfs_cache_pressure, laptop_mode, block_dump, swap_token_timeout,
drop-caches, hugepages_treat_as_movable:
block_dump
See Documentation/filesystems/proc.txt
block_dump enables block I/O debugging when set to a nonzero value. More
information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
==============================================================
overcommit_memory:
dirty_background_bytes
This value contains a flag that enables memory overcommitment.
Contains the amount of dirty memory at which the pdflush background writeback
daemon will start writeback.
When this flag is 0, the kernel attempts to estimate the amount
of free memory left when userspace requests more memory.
If dirty_background_bytes is written, dirty_background_ratio becomes a function
of its value (dirty_background_bytes / the amount of dirtyable system memory).
When this flag is 1, the kernel pretends there is always enough
memory until it actually runs out.
==============================================================
When this flag is 2, the kernel uses a "never overcommit"
policy that attempts to prevent any overcommit of memory.
dirty_background_ratio
This feature can be very useful because there are a lot of
programs that malloc() huge amounts of memory "just-in-case"
and don't use much of it.
Contains, as a percentage of total system memory, the number of pages at which
the pdflush background writeback daemon will start writing out dirty data.
The default value is 0.
==============================================================
See Documentation/vm/overcommit-accounting and
security/commoncap.c::cap_vm_enough_memory() for more information.
dirty_bytes
Contains the amount of dirty memory at which a process generating disk writes
will itself start writeback.
If dirty_bytes is written, dirty_ratio becomes a function of its value
(dirty_bytes / the amount of dirtyable system memory).
==============================================================
overcommit_ratio:
dirty_expire_centisecs
When overcommit_memory is set to 2, the committed address
space is not permitted to exceed swap plus this percentage
of physical RAM. See above.
This tunable is used to define when dirty data is old enough to be eligible
for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
Data which has been dirty in-memory for longer than this interval will be
written out next time a pdflush daemon wakes up.
==============================================================
dirty_ratio
Contains, as a percentage of total system memory, the number of pages at which
a process which is generating disk writes will itself start writing out dirty
data.
==============================================================
page-cluster:
dirty_writeback_centisecs
The Linux VM subsystem avoids excessive disk seeks by reading
multiple pages on a page fault. The number of pages it reads
is dependent on the amount of memory in your machine.
The pdflush writeback daemons will periodically wake up and write `old' data
out to disk. This tunable expresses the interval between those wakeups, in
100'ths of a second.
The number of pages the kernel reads in at once is equal to
2 ^ page-cluster. Values above 2 ^ 5 don't make much sense
for swap because we only cluster swap data in 32-page groups.
Setting this to zero disables periodic writeback altogether.
==============================================================
drop_caches
Writing to this will cause the kernel to drop clean caches, dentries and
inodes from memory, causing that memory to become free.
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation and dirty objects are not freeable, the
user should run `sync' first.
==============================================================
hugepages_treat_as_movable
This parameter is only useful when kernelcore= is specified at boot time to
create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages
are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero
value written to hugepages_treat_as_movable allows huge pages to be allocated
from ZONE_MOVABLE.
Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge
pages pool can easily grow or shrink within. Assuming that applications are
not running that mlock() a lot of memory, it is likely the huge pages pool
can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value
into nr_hugepages and triggering page reclaim.
==============================================================
hugetlb_shm_group
hugetlb_shm_group contains group id that is allowed to create SysV
shared memory segment using hugetlb page.
==============================================================
laptop_mode
laptop_mode is a knob that controls "laptop mode". All the things that are
controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt.
==============================================================
legacy_va_layout
If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
will use the legacy (2.4) layout for all processes.
==============================================================
lowmem_reserve_ratio
For some specialised workloads on highmem machines it is dangerous for
the kernel to allow process memory to be allocated from the "lowmem"
zone. This is because that memory could then be pinned via the mlock()
system call, or by unavailability of swapspace.
And on large highmem machines this lack of reclaimable lowmem memory
can be fatal.
So the Linux page allocator has a mechanism which prevents allocations
which _could_ use highmem from using too much lowmem. This means that
a certain amount of lowmem is defended from the possibility of being
captured into pinned user memory.
(The same argument applies to the old 16 megabyte ISA DMA region. This
mechanism will also defend that region from allocations which could use
highmem or lowmem).
The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
in defending these lower zones.
If you have a machine which uses highmem or ISA DMA and your
applications are using mlock(), or if you are running with no swap then
you probably should change the lowmem_reserve_ratio setting.
The lowmem_reserve_ratio is an array. You can see them by reading this file.
-
% cat /proc/sys/vm/lowmem_reserve_ratio
256 256 32
-
Note: # of this elements is one fewer than number of zones. Because the highest
zone's value is not necessary for following calculation.
But, these values are not used directly. The kernel calculates # of protection
pages for each zones from them. These are shown as array of protection pages
in /proc/zoneinfo like followings. (This is an example of x86-64 box).
Each zone has an array of protection pages like this.
-
Node 0, zone DMA
pages free 1355
min 3
low 3
high 4
:
:
numa_other 0
protection: (0, 2004, 2004, 2004)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pagesets
cpu: 0 pcp: 0
:
-
These protections are added to score to judge whether this zone should be used
for page allocation or should be reclaimed.
In this example, if normal pages (index=2) are required to this DMA zone and
pages_high is used for watermark, the kernel judges this zone should not be
used because pages_free(1355) is smaller than watermark + protection[2]
(4 + 2004 = 2008). If this protection value is 0, this zone would be used for
normal page requirement. If requirement is DMA zone(index=0), protection[0]
(=0) is used.
zone[i]'s protection[j] is calculated by following expression.
(i < j):
zone[i]->protection[j]
= (total sums of present_pages from zone[i+1] to zone[j] on the node)
/ lowmem_reserve_ratio[i];
(i = j):
(should not be protected. = 0;
(i > j):
(not necessary, but looks 0)
The default values of lowmem_reserve_ratio[i] are
256 (if zone[i] means DMA or DMA32 zone)
32 (others).
As above expression, they are reciprocal number of ratio.
256 means 1/256. # of protection pages becomes about "0.39%" of total present
pages of higher zones on the node.
If you would like to protect more pages, smaller values are effective.
The minimum value is 1 (1/1 -> 100%).
==============================================================
......@@ -124,116 +286,140 @@ become subtly broken, and prone to deadlock under high loads.
Setting this too high will OOM your machine instantly.
=============================================================
min_slab_ratio:
This is available only on NUMA kernels.
A percentage of the total pages in each zone. On Zone reclaim
(fallback from the local zone occurs) slabs will be reclaimed if more
than this percentage of pages in a zone are reclaimable slab pages.
This insures that the slab growth stays under control even in NUMA
systems that rarely perform global reclaim.
The default is 5 percent.
Note that slab reclaim is triggered in a per zone / node fashion.
The process of reclaiming slab memory is currently not node specific
and may not be fast.
=============================================================
min_unmapped_ratio:
This is available only on NUMA kernels.
A percentage of the total pages in each zone. Zone reclaim will only
occur if more than this percentage of pages are file backed and unmapped.
This is to insure that a minimal amount of local pages is still available for
file I/O even if the node is overallocated.
The default is 1 percent.
==============================================================
percpu_pagelist_fraction
mmap_min_addr
This is the fraction of pages at most (high mark pcp->high) in each zone that
are allocated for each per cpu page list. The min value for this is 8. It
means that we don't allow more than 1/8th of pages in each zone to be
allocated in any single per_cpu_pagelist. This entry only changes the value
of hot per cpu pagelists. User can specify a number like 100 to allocate
1/100th of each zone to each per cpu page list.
This file indicates the amount of address space which a user process will
be restricted from mmaping. Since kernel null dereference bugs could
accidentally operate based on the information in the first couple of pages
of memory userspace processes should not be allowed to write to them. By
default this value is set to 0 and no protections will be enforced by the
security module. Setting this value to something like 64k will allow the
vast majority of applications to work correctly and provide defense in depth
against future potential kernel bugs.
The batch value of each per cpu pagelist is also updated as a result. It is
set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
==============================================================
The initial value is zero. Kernel does not use this value at boot time to set
the high water marks for each per cpu page list.
nr_hugepages
===============================================================
Change the minimum size of the hugepage pool.
zone_reclaim_mode:
See Documentation/vm/hugetlbpage.txt
Zone_reclaim_mode allows someone to set more or less aggressive approaches to
reclaim memory when a zone runs out of memory. If it is set to zero then no
zone reclaim occurs. Allocations will be satisfied from other zones / nodes
in the system.
==============================================================
This is value ORed together of
nr_overcommit_hugepages
1 = Zone reclaim on
2 = Zone reclaim writes dirty pages out
4 = Zone reclaim swaps pages
Change the maximum size of the hugepage pool. The maximum is
nr_hugepages + nr_overcommit_hugepages.
zone_reclaim_mode is set during bootup to 1 if it is determined that pages
from remote zones will cause a measurable performance reduction. The
page allocator will then reclaim easily reusable pages (those page
cache pages that are currently not used) before allocating off node pages.
See Documentation/vm/hugetlbpage.txt
It may be beneficial to switch off zone reclaim if the system is
used for a file server and all of memory should be used for caching files
from disk. In that case the caching effect is more important than
data locality.
==============================================================
Allowing zone reclaim to write out pages stops processes that are
writing large amounts of data from dirtying pages on other nodes. Zone
reclaim will write out dirty pages if a zone fills up and so effectively
throttle the process. This may decrease the performance of a single process
since it cannot use all of system memory to buffer the outgoing writes
anymore but it preserve the memory on other nodes so that the performance
of other processes running on other nodes will not be affected.
nr_pdflush_threads
Allowing regular swap effectively restricts allocations to the local
node unless explicitly overridden by memory policies or cpuset
configurations.
The current number of pdflush threads. This value is read-only.
The value changes according to the number of dirty pages in the system.
=============================================================
When neccessary, additional pdflush threads are created, one per second, up to
nr_pdflush_threads_max.
min_unmapped_ratio:
==============================================================
This is available only on NUMA kernels.
nr_trim_pages
A percentage of the total pages in each zone. Zone reclaim will only
occur if more than this percentage of pages are file backed and unmapped.
This is to insure that a minimal amount of local pages is still available for
file I/O even if the node is overallocated.
This is available only on NOMMU kernels.
The default is 1 percent.
This value adjusts the excess page trimming behaviour of power-of-2 aligned
NOMMU mmap allocations.
=============================================================
A value of 0 disables trimming of allocations entirely, while a value of 1
trims excess pages aggressively. Any value >= 1 acts as the watermark where
trimming of allocations is initiated.
min_slab_ratio:
The default value is 1.
This is available only on NUMA kernels.
See Documentation/nommu-mmap.txt for more information.
A percentage of the total pages in each zone. On Zone reclaim
(fallback from the local zone occurs) slabs will be reclaimed if more
than this percentage of pages in a zone are reclaimable slab pages.
This insures that the slab growth stays under control even in NUMA
systems that rarely perform global reclaim.
==============================================================
The default is 5 percent.
numa_zonelist_order
Note that slab reclaim is triggered in a per zone / node fashion.
The process of reclaiming slab memory is currently not node specific
and may not be fast.
This sysctl is only for NUMA.
'where the memory is allocated from' is controlled by zonelists.
(This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation.
you may be able to read ZONE_DMA as ZONE_DMA32...)
=============================================================
In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following.
ZONE_NORMAL -> ZONE_DMA
This means that a memory allocation request for GFP_KERNEL will
get memory from ZONE_DMA only when ZONE_NORMAL is not available.
panic_on_oom
In NUMA case, you can think of following 2 types of order.
Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL
This enables or disables panic on out-of-memory feature.
(A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL
(B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA.
If this is set to 0, the kernel will kill some rogue process,
called oom_killer. Usually, oom_killer can kill rogue processes and
system will survive.
Type(A) offers the best locality for processes on Node(0), but ZONE_DMA
will be used before ZONE_NORMAL exhaustion. This increases possibility of
out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small.
If this is set to 1, the kernel panics when out-of-memory happens.
However, if a process limits using nodes by mempolicy/cpusets,
and those nodes become memory exhaustion status, one process
may be killed by oom-killer. No panic occurs in this case.
Because other nodes' memory may be free. This means system total status
may be not fatal yet.
Type(B) cannot offer the best locality but is more robust against OOM of
the DMA zone.
If this is set to 2, the kernel panics compulsorily even on the
above-mentioned.
Type(A) is called as "Node" order. Type (B) is "Zone" order.
The default value is 0.
1 and 2 are for failover of clustering. Please select either
according to your policy of failover.
"Node order" orders the zonelists by node, then by zone within each node.
Specify "[Nn]ode" for zone order
=============================================================
"Zone Order" orders the zonelists by zone type, then by node within each
zone. Specify "[Zz]one"for zode order.
Specify "[Dd]efault" to request automatic configuration. Autoconfiguration
will select "node" order in following case.
(1) if the DMA zone does not exist or
(2) if the DMA zone comprises greater than 50% of the available memory or
(3) if any node's DMA zone comprises greater than 60% of its local memory and
the amount of local memory is big enough.
Otherwise, "zone" order will be selected. Default order is recommended unless
this is causing problems for your system/application.
==============================================================
oom_dump_tasks
......@@ -254,7 +440,7 @@ OOM killer actually kills a memory-hogging task.
The default value is 0.
=============================================================
==============================================================
oom_kill_allocating_task
......@@ -277,92 +463,157 @@ The default value is 0.
==============================================================
mmap_min_addr
overcommit_memory:
This file indicates the amount of address space which a user process will
be restricted from mmaping. Since kernel null dereference bugs could
accidentally operate based on the information in the first couple of pages
of memory userspace processes should not be allowed to write to them. By
default this value is set to 0 and no protections will be enforced by the
security module. Setting this value to something like 64k will allow the
vast majority of applications to work correctly and provide defense in depth
against future potential kernel bugs.
This value contains a flag that enables memory overcommitment.
When this flag is 0, the kernel attempts to estimate the amount
of free memory left when userspace requests more memory.
When this flag is 1, the kernel pretends there is always enough
memory until it actually runs out.
When this flag is 2, the kernel uses a "never overcommit"
policy that attempts to prevent any overcommit of memory.
This feature can be very useful because there are a lot of
programs that malloc() huge amounts of memory "just-in-case"
and don't use much of it.
The default value is 0.
See Documentation/vm/overcommit-accounting and
security/commoncap.c::cap_vm_enough_memory() for more information.
==============================================================
numa_zonelist_order
overcommit_ratio:
This sysctl is only for NUMA.
'where the memory is allocated from' is controlled by zonelists.
(This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation.
you may be able to read ZONE_DMA as ZONE_DMA32...)
When overcommit_memory is set to 2, the committed address
space is not permitted to exceed swap plus this percentage
of physical RAM. See above.
In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following.
ZONE_NORMAL -> ZONE_DMA
This means that a memory allocation request for GFP_KERNEL will
get memory from ZONE_DMA only when ZONE_NORMAL is not available.
==============================================================
In NUMA case, you can think of following 2 types of order.
Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL
page-cluster
(A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL
(B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA.
page-cluster controls the number of pages which are written to swap in
a single attempt. The swap I/O size.
Type(A) offers the best locality for processes on Node(0), but ZONE_DMA
will be used before ZONE_NORMAL exhaustion. This increases possibility of
out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small.
It is a logarithmic value - setting it to zero means "1 page", setting
it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
Type(B) cannot offer the best locality but is more robust against OOM of
the DMA zone.
The default value is three (eight pages at a time). There may be some
small benefits in tuning this to a different value if your workload is
swap-intensive.
Type(A) is called as "Node" order. Type (B) is "Zone" order.
=============================================================
"Node order" orders the zonelists by node, then by zone within each node.
Specify "[Nn]ode" for zone order
panic_on_oom
"Zone Order" orders the zonelists by zone type, then by node within each
zone. Specify "[Zz]one"for zode order.
This enables or disables panic on out-of-memory feature.
Specify "[Dd]efault" to request automatic configuration. Autoconfiguration
will select "node" order in following case.
(1) if the DMA zone does not exist or
(2) if the DMA zone comprises greater than 50% of the available memory or
(3) if any node's DMA zone comprises greater than 60% of its local memory and
the amount of local memory is big enough.
If this is set to 0, the kernel will kill some rogue process,
called oom_killer. Usually, oom_killer can kill rogue processes and
system will survive.
Otherwise, "zone" order will be selected. Default order is recommended unless
this is causing problems for your system/application.
If this is set to 1, the kernel panics when out-of-memory happens.
However, if a process limits using nodes by mempolicy/cpusets,
and those nodes become memory exhaustion status, one process
may be killed by oom-killer. No panic occurs in this case.
Because other nodes' memory may be free. This means system total status
may be not fatal yet.
If this is set to 2, the kernel panics compulsorily even on the
above-mentioned.
The default value is 0.
1 and 2 are for failover of clustering. Please select either
according to your policy of failover.
=============================================================
percpu_pagelist_fraction
This is the fraction of pages at most (high mark pcp->high) in each zone that
are allocated for each per cpu page list. The min value for this is 8. It
means that we don't allow more than 1/8th of pages in each zone to be
allocated in any single per_cpu_pagelist. This entry only changes the value
of hot per cpu pagelists. User can specify a number like 100 to allocate
1/100th of each zone to each per cpu page list.
The batch value of each per cpu pagelist is also updated as a result. It is
set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
The initial value is zero. Kernel does not use this value at boot time to set
the high water marks for each per cpu page list.
==============================================================
nr_hugepages
stat_interval
Change the minimum size of the hugepage pool.
The time interval between which vm statistics are updated. The default
is 1 second.
See Documentation/vm/hugetlbpage.txt
==============================================================
swappiness
This control is used to define how aggressive the kernel will swap
memory pages. Higher values will increase agressiveness, lower values
descrease the amount of swap.
The default value is 60.
==============================================================
nr_overcommit_hugepages
vfs_cache_pressure
------------------
Change the maximum size of the hugepage pool. The maximum is
nr_hugepages + nr_overcommit_hugepages.
Controls the tendency of the kernel to reclaim the memory which is used for
caching of directory and inode objects.
See Documentation/vm/hugetlbpage.txt
At the default value of vfs_cache_pressure=100 the kernel will attempt to
reclaim dentries and inodes at a "fair" rate with respect to pagecache and
swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
causes the kernel to prefer to reclaim dentries and inodes.
==============================================================
nr_trim_pages
zone_reclaim_mode:
This is available only on NOMMU kernels.
Zone_reclaim_mode allows someone to set more or less aggressive approaches to
reclaim memory when a zone runs out of memory. If it is set to zero then no
zone reclaim occurs. Allocations will be satisfied from other zones / nodes
in the system.
This value adjusts the excess page trimming behaviour of power-of-2 aligned
NOMMU mmap allocations.
This is value ORed together of
A value of 0 disables trimming of allocations entirely, while a value of 1
trims excess pages aggressively. Any value >= 1 acts as the watermark where
trimming of allocations is initiated.
1 = Zone reclaim on
2 = Zone reclaim writes dirty pages out
4 = Zone reclaim swaps pages
The default value is 1.
zone_reclaim_mode is set during bootup to 1 if it is determined that pages
from remote zones will cause a measurable performance reduction. The
page allocator will then reclaim easily reusable pages (those page
cache pages that are currently not used) before allocating off node pages.
See Documentation/nommu-mmap.txt for more information.
It may be beneficial to switch off zone reclaim if the system is
used for a file server and all of memory should be used for caching files
from disk. In that case the caching effect is more important than
data locality.
Allowing zone reclaim to write out pages stops processes that are
writing large amounts of data from dirtying pages on other nodes. Zone
reclaim will write out dirty pages if a zone fills up and so effectively
throttle the process. This may decrease the performance of a single process
since it cannot use all of system memory to buffer the outgoing writes
anymore but it preserve the memory on other nodes so that the performance
of other processes running on other nodes will not be affected.
Allowing regular swap effectively restricts allocations to the local
node unless explicitly overridden by memory policies or cpuset
configurations.
============ End of Document =================================
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