slabinfo(5) File Formats Manual slabinfo(5)
NAME
slabinfo - kernel slab allocator statistics
SYNOPSIS
cat /proc/slabinfo
DESCRIPTION
Frequently used objects in the Linux kernel (buffer heads, inodes, den-
tries, etc.) have their own cache. The file /proc/slabinfo gives sta-
tistics 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 ap-
plication 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 corre-
sponding 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 tun-
ables for a particular cache can be set by writing lines of the follow-
ing 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 set-
tings 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 sta-
tistics fields in each line, and the first line of the file will contain
the string "(statistics)". The statistics field include : the high wa-
ter mark of active objects; the number of times objects have been allo-
cated; 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 re-
moved from this cache); and the number of times there was an error allo-
cating new pages to this cache.
VERSIONS
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 dif-
ferent 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.
NOTES
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.
SEE ALSO
slabtop(1)
The kernel source file Documentation/vm/slub.txt and
tools/vm/slabinfo.c.
Linux man-pages 6.9.1 2024-05-02 slabinfo(5)
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