slabinfo

SLABINFO(5)                      Linux manual                      SLABINFO(5)



NAME
       /proc/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
       statistics. For example:

              % cat /proc/slabinfo
              slabinfo - version: 1.1
              kmem_cache            60     78    100    2    2    1
              blkdev_requests     5120   5120     96  128  128    1
              mnt_cache             20     40     96    1    1    1
              inode_cache         7005  14792    480 1598 1849    1
              dentry_cache        5469   5880    128  183  196    1
              filp                 726    760     96   19   19    1
              buffer_head        67131  71240     96 1776 1781    1
              vm_area_struct      1204   1652     64   23   28    1
              ...
              size-8192              1     17   8192    1   17    2
              size-4096             41     73   4096   41   73    1
              ...

       For  each  slab  cache,  the cache name, the number of currently active
       objects, the total number of available objects, the size of each object
       in  bytes,  the  number  of  pages with at least one active object, the
       total number of allocated pages, and the number of pages per  slab  are
       given.

       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  compiled  with  slab cache statistics will also have "(statis-
       tics)" in the first line of output, and will have 5 additional columns,
       namely:  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.  If slab cache
       statistics are not enabled for this kernel, these columns will  not  be
       shown.

       SMP  systems  will  also  have "(SMP)" in the first line of output, and
       will have two additional columns for  each  slab,  reporting  the  slab
       allocation  policy  for  the  CPU-local  cache  (to reduce the need for
       inter-CPU synchronization when allocating objects from the cache).  The
       first  column  is the per-CPU limit: the maximum number of objects that
       will be cached for each CPU.  The second column is the batchcount:  the
       maximum  number of free objects in the global cache that will be trans-
       ferred to the per-CPU cache if it is empty, or the number of objects to
       be returned to the global cache if the per-CPU cache is full.

       If  both  slab cache statistics and SMP are defined, there will be four
       additional columns, reporting the per-CPU cache statistics.  The  first
       two are the per-CPU cache allocation hit and miss counts: the number of
       times an object was or was not available in the per-CPU cache for allo-
       cation.   The  next two are the per-CPU cache free hit and miss counts:
       the number of times a freed object could or could not  fit  within  the
       per-CPU cache limit, before flushing objects to the global cache.

       It  is possible to tune the SMP per-CPU slab cache limit and batchcount
       via:

       echo "cache_name limit batchcount" > /proc/slabinfo


AVAILABILITY
       /proc/slabinfo exists since Linux 2.1.23.   SMP  per-CPU  caches  exist
       since Linux 2.4.0-test3.


FILES
       <linux/slab.h>



                                  2001-06-19                       SLABINFO(5)