slabinfo(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | VERSIONS | NOTES | SEE ALSO | COLOPHON

SLABINFO(5)             Linux Programmer's Manual            SLABINFO(5)

NAME         top

       slabinfo - kernel slab allocator statistics

SYNOPSIS         top

       cat /proc/slabinfo

DESCRIPTION         top

       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.

VERSIONS         top

       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.

NOTES         top

       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         top

       slabtop(1)

       The kernel source file Documentation/vm/slub.txt and
       tools/vm/slabinfo.c.

COLOPHON         top

       This page is part of release 5.12 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/.

                               2021-03-22                    SLABINFO(5)

Pages that refer to this page: proc(5)