slabinfo — kernel slab allocator statistics
cat /proc/slabinfo
Frequently used objects in the Linux kernel (buffer heads,
inodes, dentries, etc.) have their own cache. The file
/proc/slabinfo gives statistics
on these caches. The following (edited) output shows an
example of the contents of this file:
$ sudo cat /proc/slabinfo
slabinfo − version: 2.1
# name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> ...
sigqueue 100 100 160 25 1 : tunables 0 0 0 : slabdata 4 4 0
sighand_cache 355 405 2112 15 8 : tunables 0 0 0 : slabdata 27 27 0
kmalloc−8192 96 96 8192 4 8 : tunables 0 0 0 : slabdata 24 24 0
...
The first line of output includes a version number, which allows an application that is reading the file to handle changes in the file format. (See VERSIONS, below.) The next line lists the names of the columns in the remaining lines.
Each of the remaining lines displays information about a specified cache. Following the cache name, the output shown in each line shows three components for each cache:
statistics
tunables
slabdata
The statistics are as follows:
active_objsThe number of objects that are currently active (i.e., in use).
num_objsThe total number of allocated objects (i.e., objects that are both in use and not in use).
objsizeThe size of objects in this slab, in bytes.
objperslabThe number of objects stored in each slab.
pagesperslabThe number of pages allocated for each slab.
The tunables
entries in each line show tunable parameters for the
corresponding cache. When using the default SLUB allocator,
there are no tunables, the /proc/slabinfo file is not writable, and
the value 0 is shown in these fields. When using the older
SLAB allocator, the tunables for a particular cache can be
set by writing lines of the following form to /proc/slabinfo:
# echo 'name limit batchcount sharedfactor' > /proc/slabinfo
Here, name is
the cache name, and limit, batchcount, and sharedfactor are integers
defining new values for the corresponding tunables. The
limit value should
be a positive value, batchcount should be a
positive value that is less than or equal to limit, and sharedfactor should be
nonnegative. If any of the specified values is invalid, the
cache settings are left unchanged.
The tunables
entries in each line contain the following fields:
limitThe maximum number of objects that will be cached.
batchcountOn SMP systems, this specifies the number of objects to transfer at one time when refilling the available object list.
sharedfactor[To be documented]
The slabdata
entries in each line contain the following fields:
active_slabsThe number of active slabs.
nums_slabsThe total number of slabs.
sharedavail[To be documented]
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 configured with CONFIG_DEBUG_SLAB will also have additional
statistics fields in each line, and the first line of the
file will contain the string "(statistics)". The statistics
field include : 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.
The /proc/slabinfo file
first appeared in Linux 2.1.23. The file is versioned, and
over time there have been a number of versions with different
layouts:
Present throughout the Linux 2.2.x kernel series.
Present in the Linux 2.4.x kernel series.
A format that was briefly present in the Linux 2.5 development series.
Present in Linux 2.6.x kernels up to and including Linux 2.6.9.
The current format, which first appeared in Linux 2.6.10.
Only root can read and (if the kernel was configured with
CONFIG_SLAB) write the
/proc/slabinfo file.
The total amount of memory allocated to the SLAB/SLUB
cache is shown in the Slab field of /proc/meminfo.
This page is part of release 5.11 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
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Copyright (c) 2001 Andreas Dilger (adilgerturbolinux.com) and Copyright (c) 2017 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |