NAME
/proc/slabinfo - Kernel slab allocator statistics
SYNOPSIS
cat /proc/slabinfo
DESCRIPTION
Frequently used objects in the Linux kernel (buffer heads, inodes,
dentries, etc.) have their own cache. The file /proc/slabinfo gives
statistics. For example:
% cat /proc/slabinfo
slabinfo - version: 1.1
kmem_cache 60 78 100 2 2 1
blkdev_requests 5120 5120 96 128 128 1
mnt_cache 20 40 96 1 1 1
inode_cache 7005 14792 480 1598 1849 1
dentry_cache 5469 5880 128 183 196 1
filp 726 760 96 19 19 1
buffer_head 67131 71240 96 1776 1781 1
vm_area_struct 1204 1652 64 23 28 1
...
size-8192 1 17 8192 1 17 2
size-4096 41 73 4096 41 73 1
...
For each slab cache, the cache name, the number of currently active
objects, the total number of available objects, the size of each object
in bytes, the number of pages with at least one active object, the
total number of allocated pages, and the number of pages per slab are
given.
Note that because of object alignment and slab cache overhead, objects
are not normally packed tightly into pages. Pages with even one in-use
object are considered in-use and cannot be freed.
Kernels compiled with slab cache statistics will also have
"(statistics)" in the first line of output, and will have 5 additional
columns, namely: the high water mark of active objects; the number of
times objects have been allocated; the number of times the cache has
grown (new pages added to this cache); the number of times the cache
has been reaped (unused pages removed from this cache); and the number
of times there was an error allocating new pages to this cache. If
slab cache statistics are not enabled for this kernel, these columns
will not be shown.
SMP systems will also have "(SMP)" in the first line of output, and
will have two additional columns for each slab, reporting the slab
allocation policy for the CPU-local cache (to reduce the need for
inter-CPU synchronization when allocating objects from the cache). The
first column is the per-CPU limit: the maximum number of objects that
will be cached for each CPU. The second column is the batchcount: the
maximum number of free objects in the global cache that will be
transferred to the per-CPU cache if it is empty, or the number of
objects to be returned to the global cache if the per-CPU cache is
full.
If both slab cache statistics and SMP are defined, there will be four
additional columns, reporting the per-CPU cache statistics. The first
two are the per-CPU cache allocation hit and miss counts: the number of
times an object was or was not available in the per-CPU cache for
allocation. The next two are the per-CPU cache free hit and miss
counts: the number of times a freed object could or could not fit
within the per-CPU cache limit, before flushing objects to the global
cache.
It is possible to tune the SMP per-CPU slab cache limit and batchcount
via:
echo "cache_name limit batchcount" > /proc/slabinfo
FILES
<linux/slab.h>
VERSIONS
/proc/slabinfo exists since Linux 2.1.23. SMP per-CPU caches exist
since Linux 2.4.0-test3.
NOTES
Since Linux 2.6.16 the file /proc/slabinfo is only present if the
CONFIG_SLAB kernel configuration option is enabled.
COLOPHON
This page is part of release 3.24 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2007-09-30