slabinfo

SLABINFO(5)                Linux Programmer's 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 exam-
       ple 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 for-
       mat.  (See VERSIONS, below.)  The next line lists the names of the col-
       umns 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  cor-
       responding  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
       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
       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.

COLOPHON
       This page is part of release 5.05 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/.

                                  2017-09-15                       SLABINFO(5)