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[thirdparty/man-pages.git] / man5 / slabinfo.5

.\" Copyright (c) 2001 Andreas Dilger (adilger@turbolinux.com)
.\"
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.\"
.\" FIXME Over time, the slabinfo format has gone through
.\" version changes. These should be documented:
.\"
.\"     slabinfo 1.0 - Linux 2.2 (precisely: 2.1.23)
.\"     slabinfo 1.1 - Linux 2.4 (precisely: 2.4.0-test3)
.\"     slabinfo 1.2 - Linux 2.5.45
.\"     slabinfo 2.0 - Linux 2.6 (precisely: 2.5.71)
.\"     slabinfo 2.1 - Linux 2.6.10
.\"
.TH SLABINFO 5 2007-09-30 "" "Linux Programmer's Manual"
.SH NAME
/proc/slabinfo \- kernel slab allocator statistics
.SH SYNOPSIS
.B cat /proc/slabinfo
.SH DESCRIPTION
Frequently used objects in the Linux kernel
(buffer heads, inodes, dentries, etc.)
have their own cache.
The file
.I /proc/slabinfo
gives statistics.
For example:
.LP
.in +4n
.nf
% 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
\&...
.fi
.in
.LP
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:

.in +4n
.nf
echo "\fIcache_name limit batchcount\fP" > /proc/slabinfo
.fi
.in
.SH FILES
.I <linux/slab.h>
.SH VERSIONS
.I /proc/slabinfo
exists since Linux 2.1.23.
SMP per-CPU caches exist since Linux 2.4.0-test3.
.SH NOTES
Since Linux 2.6.16 the file
.I /proc/slabinfo
is only present if the
.B CONFIG_SLAB
kernel configuration option is enabled.