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.