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NAME | SYNOPSIS | DESCRIPTION | VERSIONS | NOTES | SEE ALSO | COLOPHON |
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slabinfo(5) File Formats Manual slabinfo(5)
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_objs
The number of objects that are currently active (i.e., in
use).
num_objs
The total number of allocated objects (i.e., objects that
are both in use and not in use).
objsize
The size of objects in this slab, in bytes.
objperslab
The number of objects stored in each slab.
pagesperslab
The 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:
limit The maximum number of objects that will be cached.
batchcount
On 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_slabs
The number of active slabs.
nums_slabs
The 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:
1.0 Present throughout the Linux 2.2.x kernel series.
1.1 Present in the Linux 2.4.x kernel series.
1.2 A format that was briefly present in the Linux 2.5
development series.
2.0 Present in Linux 2.6.x kernels up to and including Linux
2.6.9.
2.1 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.
slabtop(1)
The kernel source file Documentation/vm/slub.txt and
tools/vm/slabinfo.c.
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.9.1 2024-05-02 slabinfo(5)
Pages that refer to this page: proc(5), proc_meminfo(5), proc_slabinfo(5), vmstat(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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