895 lines
33 KiB
Plaintext
895 lines
33 KiB
Plaintext
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 2.6.29.
|
|
|
|
The files in this directory can be used to tune the operation
|
|
of the virtual memory (VM) subsystem of the Linux kernel and
|
|
the writeout of dirty data to disk.
|
|
|
|
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:
|
|
|
|
- admin_reserve_kbytes
|
|
- block_dump
|
|
- compact_memory
|
|
- compact_unevictable_allowed
|
|
- dirty_background_bytes
|
|
- dirty_background_ratio
|
|
- dirty_bytes
|
|
- dirty_expire_centisecs
|
|
- dirty_ratio
|
|
- dirty_writeback_centisecs
|
|
- drop_caches
|
|
- extfrag_threshold
|
|
- extra_free_kbytes
|
|
- hugepages_treat_as_movable
|
|
- hugetlb_shm_group
|
|
- laptop_mode
|
|
- legacy_va_layout
|
|
- lowmem_reserve_ratio
|
|
- max_map_count
|
|
- memory_failure_early_kill
|
|
- memory_failure_recovery
|
|
- min_free_kbytes
|
|
- min_slab_ratio
|
|
- min_unmapped_ratio
|
|
- mmap_min_addr
|
|
- mmap_rnd_bits
|
|
- mmap_rnd_compat_bits
|
|
- nr_hugepages
|
|
- nr_overcommit_hugepages
|
|
- nr_trim_pages (only if CONFIG_MMU=n)
|
|
- numa_zonelist_order
|
|
- oom_dump_tasks
|
|
- oom_kill_allocating_task
|
|
- overcommit_kbytes
|
|
- overcommit_memory
|
|
- overcommit_ratio
|
|
- page-cluster
|
|
- panic_on_oom
|
|
- percpu_pagelist_fraction
|
|
- stat_interval
|
|
- stat_refresh
|
|
- swappiness
|
|
- user_reserve_kbytes
|
|
- vfs_cache_pressure
|
|
- watermark_scale_factor
|
|
- zone_reclaim_mode
|
|
|
|
==============================================================
|
|
|
|
admin_reserve_kbytes
|
|
|
|
The amount of free memory in the system that should be reserved for users
|
|
with the capability cap_sys_admin.
|
|
|
|
admin_reserve_kbytes defaults to min(3% of free pages, 8MB)
|
|
|
|
That should provide enough for the admin to log in and kill a process,
|
|
if necessary, under the default overcommit 'guess' mode.
|
|
|
|
Systems running under overcommit 'never' should increase this to account
|
|
for the full Virtual Memory Size of programs used to recover. Otherwise,
|
|
root may not be able to log in to recover the system.
|
|
|
|
How do you calculate a minimum useful reserve?
|
|
|
|
sshd or login + bash (or some other shell) + top (or ps, kill, etc.)
|
|
|
|
For overcommit 'guess', we can sum resident set sizes (RSS).
|
|
On x86_64 this is about 8MB.
|
|
|
|
For overcommit 'never', we can take the max of their virtual sizes (VSZ)
|
|
and add the sum of their RSS.
|
|
On x86_64 this is about 128MB.
|
|
|
|
Changing this takes effect whenever an application requests memory.
|
|
|
|
==============================================================
|
|
|
|
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.
|
|
|
|
==============================================================
|
|
|
|
compact_memory
|
|
|
|
Available only when CONFIG_COMPACTION is set. When 1 is written to the file,
|
|
all zones are compacted such that free memory is available in contiguous
|
|
blocks where possible. This can be important for example in the allocation of
|
|
huge pages although processes will also directly compact memory as required.
|
|
|
|
==============================================================
|
|
|
|
compact_unevictable_allowed
|
|
|
|
Available only when CONFIG_COMPACTION is set. When set to 1, compaction is
|
|
allowed to examine the unevictable lru (mlocked pages) for pages to compact.
|
|
This should be used on systems where stalls for minor page faults are an
|
|
acceptable trade for large contiguous free memory. Set to 0 to prevent
|
|
compaction from moving pages that are unevictable. Default value is 1.
|
|
|
|
==============================================================
|
|
|
|
dirty_background_bytes
|
|
|
|
Contains the amount of dirty memory at which the background kernel
|
|
flusher threads will start writeback.
|
|
|
|
Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only
|
|
one of them may be specified at a time. When one sysctl is written it is
|
|
immediately taken into account to evaluate the dirty memory limits and the
|
|
other appears as 0 when read.
|
|
|
|
==============================================================
|
|
|
|
dirty_background_ratio
|
|
|
|
Contains, as a percentage of total available memory that contains free pages
|
|
and reclaimable pages, the number of pages at which the background kernel
|
|
flusher threads will start writing out dirty data.
|
|
|
|
The total available memory is not equal to total system memory.
|
|
|
|
==============================================================
|
|
|
|
dirty_bytes
|
|
|
|
Contains the amount of dirty memory at which a process generating disk writes
|
|
will itself start writeback.
|
|
|
|
Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be
|
|
specified at a time. When one sysctl is written it is immediately taken into
|
|
account to evaluate the dirty memory limits and the other appears as 0 when
|
|
read.
|
|
|
|
Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
|
|
value lower than this limit will be ignored and the old configuration will be
|
|
retained.
|
|
|
|
==============================================================
|
|
|
|
dirty_expire_centisecs
|
|
|
|
This tunable is used to define when dirty data is old enough to be eligible
|
|
for writeout by the kernel flusher threads. 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 flusher thread wakes up.
|
|
|
|
==============================================================
|
|
|
|
dirty_ratio
|
|
|
|
Contains, as a percentage of total available memory that contains free pages
|
|
and reclaimable pages, the number of pages at which a process which is
|
|
generating disk writes will itself start writing out dirty data.
|
|
|
|
The total available memory is not equal to total system memory.
|
|
|
|
==============================================================
|
|
|
|
dirty_writeback_centisecs
|
|
|
|
The kernel flusher threads 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.
|
|
|
|
==============================================================
|
|
|
|
drop_caches
|
|
|
|
Writing to this will cause the kernel to drop clean caches, as well as
|
|
reclaimable slab objects like dentries and inodes. Once dropped, their
|
|
memory becomes free.
|
|
|
|
To free pagecache:
|
|
echo 1 > /proc/sys/vm/drop_caches
|
|
To free reclaimable slab objects (includes dentries and inodes):
|
|
echo 2 > /proc/sys/vm/drop_caches
|
|
To free slab objects and pagecache:
|
|
echo 3 > /proc/sys/vm/drop_caches
|
|
|
|
This is a non-destructive operation and will not free any dirty objects.
|
|
To increase the number of objects freed by this operation, the user may run
|
|
`sync' prior to writing to /proc/sys/vm/drop_caches. This will minimize the
|
|
number of dirty objects on the system and create more candidates to be
|
|
dropped.
|
|
|
|
This file is not a means to control the growth of the various kernel caches
|
|
(inodes, dentries, pagecache, etc...) These objects are automatically
|
|
reclaimed by the kernel when memory is needed elsewhere on the system.
|
|
|
|
Use of this file can cause performance problems. Since it discards cached
|
|
objects, it may cost a significant amount of I/O and CPU to recreate the
|
|
dropped objects, especially if they were under heavy use. Because of this,
|
|
use outside of a testing or debugging environment is not recommended.
|
|
|
|
You may see informational messages in your kernel log when this file is
|
|
used:
|
|
|
|
cat (1234): drop_caches: 3
|
|
|
|
These are informational only. They do not mean that anything is wrong
|
|
with your system. To disable them, echo 4 (bit 3) into drop_caches.
|
|
|
|
==============================================================
|
|
|
|
extfrag_threshold
|
|
|
|
This parameter affects whether the kernel will compact memory or direct
|
|
reclaim to satisfy a high-order allocation. The extfrag/extfrag_index file in
|
|
debugfs shows what the fragmentation index for each order is in each zone in
|
|
the system. Values tending towards 0 imply allocations would fail due to lack
|
|
of memory, values towards 1000 imply failures are due to fragmentation and -1
|
|
implies that the allocation will succeed as long as watermarks are met.
|
|
|
|
The kernel will not compact memory in a zone if the
|
|
fragmentation index is <= extfrag_threshold. The default value is 500.
|
|
|
|
==============================================================
|
|
|
|
extra_free_kbytes
|
|
|
|
This parameter tells the VM to keep extra free memory between the threshold
|
|
where background reclaim (kswapd) kicks in, and the threshold where direct
|
|
reclaim (by allocating processes) kicks in.
|
|
|
|
This is useful for workloads that require low latency memory allocations
|
|
and have a bounded burstiness in memory allocations, for example a
|
|
realtime application that receives and transmits network traffic
|
|
(causing in-kernel memory allocations) with a maximum total message burst
|
|
size of 200MB may need 200MB of extra free memory to avoid direct reclaim
|
|
related latencies.
|
|
|
|
==============================================================
|
|
|
|
hugepages_treat_as_movable
|
|
|
|
This parameter controls whether we can allocate hugepages from ZONE_MOVABLE
|
|
or not. If set to non-zero, hugepages can be allocated from ZONE_MOVABLE.
|
|
ZONE_MOVABLE is created when kernel boot parameter kernelcore= is specified,
|
|
so this parameter has no effect if used without kernelcore=.
|
|
|
|
Hugepage migration is now available in some situations which depend on the
|
|
architecture and/or the hugepage size. If a hugepage supports migration,
|
|
allocation from ZONE_MOVABLE is always enabled for the hugepage regardless
|
|
of the value of this parameter.
|
|
IOW, this parameter affects only non-migratable hugepages.
|
|
|
|
Assuming that hugepages are not migratable in your system, one usecase of
|
|
this parameter is that users can make hugepage pool more extensible by
|
|
enabling the allocation from ZONE_MOVABLE. This is because on ZONE_MOVABLE
|
|
page reclaim/migration/compaction work more and you can get contiguous
|
|
memory more likely. Note that using ZONE_MOVABLE for non-migratable
|
|
hugepages can do harm to other features like memory hotremove (because
|
|
memory hotremove expects that memory blocks on ZONE_MOVABLE are always
|
|
removable,) so it's a trade-off responsible for the users.
|
|
|
|
==============================================================
|
|
|
|
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 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
|
|
watermark[WMARK_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 managed_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 managed
|
|
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%).
|
|
|
|
==============================================================
|
|
|
|
max_map_count:
|
|
|
|
This file contains the maximum number of memory map areas a process
|
|
may have. Memory map areas are used as a side-effect of calling
|
|
malloc, directly by mmap and mprotect, and also when loading shared
|
|
libraries.
|
|
|
|
While most applications need less than a thousand maps, certain
|
|
programs, particularly malloc debuggers, may consume lots of them,
|
|
e.g., up to one or two maps per allocation.
|
|
|
|
The default value is 65536.
|
|
|
|
=============================================================
|
|
|
|
memory_failure_early_kill:
|
|
|
|
Control how to kill processes when uncorrected memory error (typically
|
|
a 2bit error in a memory module) is detected in the background by hardware
|
|
that cannot be handled by the kernel. In some cases (like the page
|
|
still having a valid copy on disk) the kernel will handle the failure
|
|
transparently without affecting any applications. But if there is
|
|
no other uptodate copy of the data it will kill to prevent any data
|
|
corruptions from propagating.
|
|
|
|
1: Kill all processes that have the corrupted and not reloadable page mapped
|
|
as soon as the corruption is detected. Note this is not supported
|
|
for a few types of pages, like kernel internally allocated data or
|
|
the swap cache, but works for the majority of user pages.
|
|
|
|
0: Only unmap the corrupted page from all processes and only kill a process
|
|
who tries to access it.
|
|
|
|
The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can
|
|
handle this if they want to.
|
|
|
|
This is only active on architectures/platforms with advanced machine
|
|
check handling and depends on the hardware capabilities.
|
|
|
|
Applications can override this setting individually with the PR_MCE_KILL prctl
|
|
|
|
==============================================================
|
|
|
|
memory_failure_recovery
|
|
|
|
Enable memory failure recovery (when supported by the platform)
|
|
|
|
1: Attempt recovery.
|
|
|
|
0: Always panic on a memory failure.
|
|
|
|
==============================================================
|
|
|
|
min_free_kbytes:
|
|
|
|
This is used to force the Linux VM to keep a minimum number
|
|
of kilobytes free. The VM uses this number to compute a
|
|
watermark[WMARK_MIN] value for each lowmem zone in the system.
|
|
Each lowmem zone gets a number of reserved free pages based
|
|
proportionally on its size.
|
|
|
|
Some minimal amount of memory is needed to satisfy PF_MEMALLOC
|
|
allocations; if you set this to lower than 1024KB, your system will
|
|
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.
|
|
|
|
This is a percentage of the total pages in each zone. Zone reclaim will
|
|
only occur if more than this percentage of pages are in a state that
|
|
zone_reclaim_mode allows to be reclaimed.
|
|
|
|
If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared
|
|
against all file-backed unmapped pages including swapcache pages and tmpfs
|
|
files. Otherwise, only unmapped pages backed by normal files but not tmpfs
|
|
files and similar are considered.
|
|
|
|
The default is 1 percent.
|
|
|
|
==============================================================
|
|
|
|
mmap_min_addr
|
|
|
|
This file indicates the amount of address space which a user process will
|
|
be restricted from mmapping. 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.
|
|
|
|
==============================================================
|
|
|
|
mmap_rnd_bits:
|
|
|
|
This value can be used to select the number of bits to use to
|
|
determine the random offset to the base address of vma regions
|
|
resulting from mmap allocations on architectures which support
|
|
tuning address space randomization. This value will be bounded
|
|
by the architecture's minimum and maximum supported values.
|
|
|
|
This value can be changed after boot using the
|
|
/proc/sys/vm/mmap_rnd_bits tunable
|
|
|
|
==============================================================
|
|
|
|
mmap_rnd_compat_bits:
|
|
|
|
This value can be used to select the number of bits to use to
|
|
determine the random offset to the base address of vma regions
|
|
resulting from mmap allocations for applications run in
|
|
compatibility mode on architectures which support tuning address
|
|
space randomization. This value will be bounded by the
|
|
architecture's minimum and maximum supported values.
|
|
|
|
This value can be changed after boot using the
|
|
/proc/sys/vm/mmap_rnd_compat_bits tunable
|
|
|
|
==============================================================
|
|
|
|
nr_hugepages
|
|
|
|
Change the minimum size of the hugepage pool.
|
|
|
|
See Documentation/vm/hugetlbpage.txt
|
|
|
|
==============================================================
|
|
|
|
nr_overcommit_hugepages
|
|
|
|
Change the maximum size of the hugepage pool. The maximum is
|
|
nr_hugepages + nr_overcommit_hugepages.
|
|
|
|
See Documentation/vm/hugetlbpage.txt
|
|
|
|
==============================================================
|
|
|
|
nr_trim_pages
|
|
|
|
This is available only on NOMMU kernels.
|
|
|
|
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.
|
|
|
|
The default value is 1.
|
|
|
|
See Documentation/nommu-mmap.txt for more information.
|
|
|
|
==============================================================
|
|
|
|
numa_zonelist_order
|
|
|
|
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.
|
|
|
|
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
|
|
|
|
(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.
|
|
|
|
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.
|
|
|
|
Type(B) cannot offer the best locality but is more robust against OOM of
|
|
the DMA zone.
|
|
|
|
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 node order
|
|
|
|
"Zone Order" orders the zonelists by zone type, then by node within each
|
|
zone. Specify "[Zz]one" for zone order.
|
|
|
|
Specify "[Dd]efault" to request automatic configuration.
|
|
|
|
On 32-bit, the Normal zone needs to be preserved for allocations accessible
|
|
by the kernel, so "zone" order will be selected.
|
|
|
|
On 64-bit, devices that require DMA32/DMA are relatively rare, so "node"
|
|
order will be selected.
|
|
|
|
Default order is recommended unless this is causing problems for your
|
|
system/application.
|
|
|
|
==============================================================
|
|
|
|
oom_dump_tasks
|
|
|
|
Enables a system-wide task dump (excluding kernel threads) to be produced
|
|
when the kernel performs an OOM-killing and includes such information as
|
|
pid, uid, tgid, vm size, rss, nr_ptes, nr_pmds, swapents, oom_score_adj
|
|
score, and name. This is helpful to determine why the OOM killer was
|
|
invoked, to identify the rogue task that caused it, and to determine why
|
|
the OOM killer chose the task it did to kill.
|
|
|
|
If this is set to zero, this information is suppressed. On very
|
|
large systems with thousands of tasks it may not be feasible to dump
|
|
the memory state information for each one. Such systems should not
|
|
be forced to incur a performance penalty in OOM conditions when the
|
|
information may not be desired.
|
|
|
|
If this is set to non-zero, this information is shown whenever the
|
|
OOM killer actually kills a memory-hogging task.
|
|
|
|
The default value is 1 (enabled).
|
|
|
|
==============================================================
|
|
|
|
oom_kill_allocating_task
|
|
|
|
This enables or disables killing the OOM-triggering task in
|
|
out-of-memory situations.
|
|
|
|
If this is set to zero, the OOM killer will scan through the entire
|
|
tasklist and select a task based on heuristics to kill. This normally
|
|
selects a rogue memory-hogging task that frees up a large amount of
|
|
memory when killed.
|
|
|
|
If this is set to non-zero, the OOM killer simply kills the task that
|
|
triggered the out-of-memory condition. This avoids the expensive
|
|
tasklist scan.
|
|
|
|
If panic_on_oom is selected, it takes precedence over whatever value
|
|
is used in oom_kill_allocating_task.
|
|
|
|
The default value is 0.
|
|
|
|
==============================================================
|
|
|
|
overcommit_kbytes:
|
|
|
|
When overcommit_memory is set to 2, the committed address space is not
|
|
permitted to exceed swap plus this amount of physical RAM. See below.
|
|
|
|
Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one
|
|
of them may be specified at a time. Setting one disables the other (which
|
|
then appears as 0 when read).
|
|
|
|
==============================================================
|
|
|
|
overcommit_memory:
|
|
|
|
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.
|
|
Note that user_reserve_kbytes affects this policy.
|
|
|
|
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
|
|
mm/mmap.c::__vm_enough_memory() for more information.
|
|
|
|
==============================================================
|
|
|
|
overcommit_ratio:
|
|
|
|
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.
|
|
|
|
==============================================================
|
|
|
|
page-cluster
|
|
|
|
page-cluster controls the number of pages up to which consecutive pages
|
|
are read in from swap in a single attempt. This is the swap counterpart
|
|
to page cache readahead.
|
|
The mentioned consecutivity is not in terms of virtual/physical addresses,
|
|
but consecutive on swap space - that means they were swapped out together.
|
|
|
|
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.
|
|
Zero disables swap readahead completely.
|
|
|
|
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.
|
|
|
|
Lower values mean lower latencies for initial faults, but at the same time
|
|
extra faults and I/O delays for following faults if they would have been part of
|
|
that consecutive pages readahead would have brought in.
|
|
|
|
=============================================================
|
|
|
|
panic_on_oom
|
|
|
|
This enables or disables panic on out-of-memory feature.
|
|
|
|
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.
|
|
|
|
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. Even oom happens under memory cgroup, the whole
|
|
system panics.
|
|
|
|
The default value is 0.
|
|
1 and 2 are for failover of clustering. Please select either
|
|
according to your policy of failover.
|
|
panic_on_oom=2+kdump gives you very strong tool to investigate
|
|
why oom happens. You can get snapshot.
|
|
|
|
=============================================================
|
|
|
|
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. If the user writes '0' to this
|
|
sysctl, it will revert to this default behavior.
|
|
|
|
==============================================================
|
|
|
|
stat_interval
|
|
|
|
The time interval between which vm statistics are updated. The default
|
|
is 1 second.
|
|
|
|
==============================================================
|
|
|
|
stat_refresh
|
|
|
|
Any read or write (by root only) flushes all the per-cpu vm statistics
|
|
into their global totals, for more accurate reports when testing
|
|
e.g. cat /proc/sys/vm/stat_refresh /proc/meminfo
|
|
|
|
As a side-effect, it also checks for negative totals (elsewhere reported
|
|
as 0) and "fails" with EINVAL if any are found, with a warning in dmesg.
|
|
(At time of writing, a few stats are known sometimes to be found negative,
|
|
with no ill effects: errors and warnings on these stats are suppressed.)
|
|
|
|
==============================================================
|
|
|
|
swappiness
|
|
|
|
This control is used to define how aggressive the kernel will swap
|
|
memory pages. Higher values will increase agressiveness, lower values
|
|
decrease the amount of swap. A value of 0 instructs the kernel not to
|
|
initiate swap until the amount of free and file-backed pages is less
|
|
than the high water mark in a zone.
|
|
|
|
The default value is 60.
|
|
|
|
==============================================================
|
|
|
|
- user_reserve_kbytes
|
|
|
|
When overcommit_memory is set to 2, "never overcommit" mode, reserve
|
|
min(3% of current process size, user_reserve_kbytes) of free memory.
|
|
This is intended to prevent a user from starting a single memory hogging
|
|
process, such that they cannot recover (kill the hog).
|
|
|
|
user_reserve_kbytes defaults to min(3% of the current process size, 128MB).
|
|
|
|
If this is reduced to zero, then the user will be allowed to allocate
|
|
all free memory with a single process, minus admin_reserve_kbytes.
|
|
Any subsequent attempts to execute a command will result in
|
|
"fork: Cannot allocate memory".
|
|
|
|
Changing this takes effect whenever an application requests memory.
|
|
|
|
==============================================================
|
|
|
|
vfs_cache_pressure
|
|
------------------
|
|
|
|
This percentage value 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. When vfs_cache_pressure=0, the kernel will
|
|
never reclaim dentries and inodes due to memory pressure and this can easily
|
|
lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100
|
|
causes the kernel to prefer to reclaim dentries and inodes.
|
|
|
|
Increasing vfs_cache_pressure significantly beyond 100 may have negative
|
|
performance impact. Reclaim code needs to take various locks to find freeable
|
|
directory and inode objects. With vfs_cache_pressure=1000, it will look for
|
|
ten times more freeable objects than there are.
|
|
|
|
=============================================================
|
|
|
|
watermark_scale_factor:
|
|
|
|
This factor controls the aggressiveness of kswapd. It defines the
|
|
amount of memory left in a node/system before kswapd is woken up and
|
|
how much memory needs to be free before kswapd goes back to sleep.
|
|
|
|
The unit is in fractions of 10,000. The default value of 10 means the
|
|
distances between watermarks are 0.1% of the available memory in the
|
|
node/system. The maximum value is 1000, or 10% of memory.
|
|
|
|
A high rate of threads entering direct reclaim (allocstall) or kswapd
|
|
going to sleep prematurely (kswapd_low_wmark_hit_quickly) can indicate
|
|
that the number of free pages kswapd maintains for latency reasons is
|
|
too small for the allocation bursts occurring in the system. This knob
|
|
can then be used to tune kswapd aggressiveness accordingly.
|
|
|
|
==============================================================
|
|
|
|
zone_reclaim_mode:
|
|
|
|
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
|
|
|
|
1 = Zone reclaim on
|
|
2 = Zone reclaim writes dirty pages out
|
|
4 = Zone reclaim swaps pages
|
|
|
|
zone_reclaim_mode is disabled by default. For file servers or workloads
|
|
that benefit from having their data cached, zone_reclaim_mode should be
|
|
left disabled as the caching effect is likely to be more important than
|
|
data locality.
|
|
|
|
zone_reclaim may be enabled if it's known that the workload is partitioned
|
|
such that each partition fits within a NUMA node and that accessing remote
|
|
memory would 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.
|
|
|
|
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 =================================
|