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linux-next/Documentation/ABI/testing/sysfs-kernel-slab
Waiman Long 04f768a39d mm, slab: extend slab/shrink to shrink all memcg caches 
Currently, a value of '1" is written to /sys/kernel/slab/<slab>/shrink
file to shrink the slab by flushing out all the per-cpu slabs and free
slabs in partial lists.  This can be useful to squeeze out a bit more
memory under extreme condition as well as making the active object counts
in /proc/slabinfo more accurate.

This usually applies only to the root caches, as the SLUB_MEMCG_SYSFS_ON
option is usually not enabled and "slub_memcg_sysfs=1" not set.  Even if
memcg sysfs is turned on, it is too cumbersome and impractical to manage
all those per-memcg sysfs files in a real production system.

So there is no practical way to shrink memcg caches.  Fix this by enabling
a proper write to the shrink sysfs file of the root cache to scan all the
available memcg caches and shrink them as well.  For a non-root memcg
cache (when SLUB_MEMCG_SYSFS_ON or slub_memcg_sysfs is on), only that
cache will be shrunk when written.

On a 2-socket 64-core 256-thread arm64 system with 64k page after
a parallel kernel build, the the amount of memory occupied by slabs
before shrinking slabs were:

 # grep task_struct /proc/slabinfo
 task_struct        53137  53192   4288   61    4 : tunables    0    0
 0 : slabdata    872    872      0
 # grep "^S[lRU]" /proc/meminfo
 Slab:            3936832 kB
 SReclaimable:     399104 kB
 SUnreclaim:      3537728 kB

After shrinking slabs (by echoing "1" to all shrink files):

 # grep "^S[lRU]" /proc/meminfo
 Slab:            1356288 kB
 SReclaimable:     263296 kB
 SUnreclaim:      1092992 kB
 # grep task_struct /proc/slabinfo
 task_struct         2764   6832   4288   61    4 : tunables    0    0
 0 : slabdata    112    112      0

Link: http://lkml.kernel.org/r/20190723151445.7385-1-longman@redhat.com
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-24 15:54:07 -07:00

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What: /sys/kernel/slab
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The /sys/kernel/slab directory contains a snapshot of the
internal state of the SLUB allocator for each cache. Certain
files may be modified to change the behavior of the cache (and
any cache it aliases, if any).
Users: kernel memory tuning tools
What: /sys/kernel/slab/cache/aliases
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The aliases file is read-only and specifies how many caches
have merged into this cache.
What: /sys/kernel/slab/cache/align
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The align file is read-only and specifies the cache's object
alignment in bytes.
What: /sys/kernel/slab/cache/alloc_calls
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The alloc_calls file is read-only and lists the kernel code
locations from which allocations for this cache were performed.
The alloc_calls file only contains information if debugging is
enabled for that cache (see Documentation/vm/slub.rst).
What: /sys/kernel/slab/cache/alloc_fastpath
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The alloc_fastpath file shows how many objects have been
allocated using the fast path. It can be written to clear the
current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/alloc_from_partial
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The alloc_from_partial file shows how many times a cpu slab has
been full and it has been refilled by using a slab from the list
of partially used slabs. It can be written to clear the current
count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/alloc_refill
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The alloc_refill file shows how many times the per-cpu freelist
was empty but there were objects available as the result of
remote cpu frees. It can be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/alloc_slab
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The alloc_slab file is shows how many times a new slab had to
be allocated from the page allocator. It can be written to
clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/alloc_slowpath
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The alloc_slowpath file shows how many objects have been
allocated using the slow path because of a refill or
allocation from a partial or new slab. It can be written to
clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/cache_dma
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The cache_dma file is read-only and specifies whether objects
are from ZONE_DMA.
Available when CONFIG_ZONE_DMA is enabled.
What: /sys/kernel/slab/cache/cpu_slabs
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The cpu_slabs file is read-only and displays how many cpu slabs
are active and their NUMA locality.
What: /sys/kernel/slab/cache/cpuslab_flush
Date: April 2009
KernelVersion: 2.6.31
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The file cpuslab_flush shows how many times a cache's cpu slabs
have been flushed as the result of destroying or shrinking a
cache, a cpu going offline, or as the result of forcing an
allocation from a certain node. It can be written to clear the
current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/ctor
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The ctor file is read-only and specifies the cache's object
constructor function, which is invoked for each object when a
new slab is allocated.
What: /sys/kernel/slab/cache/deactivate_empty
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The deactivate_empty file shows how many times an empty cpu slab
was deactivated. It can be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/deactivate_full
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The deactivate_full file shows how many times a full cpu slab
was deactivated. It can be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/deactivate_remote_frees
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The deactivate_remote_frees file shows how many times a cpu slab
has been deactivated and contained free objects that were freed
remotely. It can be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/deactivate_to_head
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The deactivate_to_head file shows how many times a partial cpu
slab was deactivated and added to the head of its node's partial
list. It can be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/deactivate_to_tail
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The deactivate_to_tail file shows how many times a partial cpu
slab was deactivated and added to the tail of its node's partial
list. It can be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/destroy_by_rcu
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The destroy_by_rcu file is read-only and specifies whether
slabs (not objects) are freed by rcu.
What: /sys/kernel/slab/cache/free_add_partial
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The free_add_partial file shows how many times an object has
been freed in a full slab so that it had to added to its node's
partial list. It can be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/free_calls
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The free_calls file is read-only and lists the locations of
object frees if slab debugging is enabled (see
Documentation/vm/slub.rst).
What: /sys/kernel/slab/cache/free_fastpath
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The free_fastpath file shows how many objects have been freed
using the fast path because it was an object from the cpu slab.
It can be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/free_frozen
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The free_frozen file shows how many objects have been freed to
a frozen slab (i.e. a remote cpu slab). It can be written to
clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/free_remove_partial
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The free_remove_partial file shows how many times an object has
been freed to a now-empty slab so that it had to be removed from
its node's partial list. It can be written to clear the current
count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/free_slab
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The free_slab file shows how many times an empty slab has been
freed back to the page allocator. It can be written to clear
the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/free_slowpath
Date: February 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The free_slowpath file shows how many objects have been freed
using the slow path (i.e. to a full or partial slab). It can
be written to clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/hwcache_align
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The hwcache_align file is read-only and specifies whether
objects are aligned on cachelines.
What: /sys/kernel/slab/cache/min_partial
Date: February 2009
KernelVersion: 2.6.30
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
David Rientjes <rientjes@google.com>
Description:
The min_partial file specifies how many empty slabs shall
remain on a node's partial list to avoid the overhead of
allocating new slabs. Such slabs may be reclaimed by utilizing
the shrink file.
What: /sys/kernel/slab/cache/object_size
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The object_size file is read-only and specifies the cache's
object size.
What: /sys/kernel/slab/cache/objects
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The objects file is read-only and displays how many objects are
active and from which nodes they are from.
What: /sys/kernel/slab/cache/objects_partial
Date: April 2008
KernelVersion: 2.6.26
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The objects_partial file is read-only and displays how many
objects are on partial slabs and from which nodes they are
from.
What: /sys/kernel/slab/cache/objs_per_slab
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The file objs_per_slab is read-only and specifies how many
objects may be allocated from a single slab of the order
specified in /sys/kernel/slab/cache/order.
What: /sys/kernel/slab/cache/order
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The order file specifies the page order at which new slabs are
allocated. It is writable and can be changed to increase the
number of objects per slab. If a slab cannot be allocated
because of fragmentation, SLUB will retry with the minimum order
possible depending on its characteristics.
When debug_guardpage_minorder=N (N > 0) parameter is specified
(see Documentation/admin-guide/kernel-parameters.rst), the minimum possible
order is used and this sysfs entry can not be used to change
the order at run time.
What: /sys/kernel/slab/cache/order_fallback
Date: April 2008
KernelVersion: 2.6.26
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The order_fallback file shows how many times an allocation of a
new slab has not been possible at the cache's order and instead
fallen back to its minimum possible order. It can be written to
clear the current count.
Available when CONFIG_SLUB_STATS is enabled.
What: /sys/kernel/slab/cache/partial
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The partial file is read-only and displays how long many
partial slabs there are and how long each node's list is.
What: /sys/kernel/slab/cache/poison
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The poison file specifies whether objects should be poisoned
when a new slab is allocated.
What: /sys/kernel/slab/cache/reclaim_account
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The reclaim_account file specifies whether the cache's objects
are reclaimable (and grouped by their mobility).
What: /sys/kernel/slab/cache/red_zone
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The red_zone file specifies whether the cache's objects are red
zoned.
What: /sys/kernel/slab/cache/remote_node_defrag_ratio
Date: January 2008
KernelVersion: 2.6.25
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The file remote_node_defrag_ratio specifies the percentage of
times SLUB will attempt to refill the cpu slab with a partial
slab from a remote node as opposed to allocating a new slab on
the local node. This reduces the amount of wasted memory over
the entire system but can be expensive.
Available when CONFIG_NUMA is enabled.
What: /sys/kernel/slab/cache/sanity_checks
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The sanity_checks file specifies whether expensive checks
should be performed on free and, at minimum, enables double free
checks. Caches that enable sanity_checks cannot be merged with
caches that do not.
What: /sys/kernel/slab/cache/shrink
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The shrink file is used to reclaim unused slab cache
memory from a cache. Empty per-cpu or partial slabs
are freed and the partial list is sorted so the slabs
with the fewest available objects are used first.
It only accepts a value of "1" on write for shrinking
the cache. Other input values are considered invalid.
Shrinking slab caches might be expensive and can
adversely impact other running applications. So it
should be used with care.
What: /sys/kernel/slab/cache/slab_size
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The slab_size file is read-only and specifies the object size
with metadata (debugging information and alignment) in bytes.
What: /sys/kernel/slab/cache/slabs
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The slabs file is read-only and displays how long many slabs
there are (both cpu and partial) and from which nodes they are
from.
What: /sys/kernel/slab/cache/store_user
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The store_user file specifies whether the location of
allocation or free should be tracked for a cache.
What: /sys/kernel/slab/cache/total_objects
Date: April 2008
KernelVersion: 2.6.26
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The total_objects file is read-only and displays how many total
objects a cache has and from which nodes they are from.
What: /sys/kernel/slab/cache/trace
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
The trace file specifies whether object allocations and frees
should be traced.
What: /sys/kernel/slab/cache/validate
Date: May 2007
KernelVersion: 2.6.22
Contact: Pekka Enberg <penberg@cs.helsinki.fi>,
Christoph Lameter <cl@linux-foundation.org>
Description:
Writing to the validate file causes SLUB to traverse all of its
cache's objects and check the validity of metadata.
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