NAME

       slabinfo - kernel slab allocator statistics

SYNOPSIS

       cat /proc/slabinfo

DESCRIPTION

       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

       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

       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.