man5/slabinfo.5

   1 .\" Copyright (c) 2001 Andreas Dilger (adilger@turbolinux.com)
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  23 .TH SLABINFO 5 2001-06-19 "" "Linux manual"
  24 .SH NAME
  25 /proc/slabinfo \- Kernel slab allocator statistics
  26 .SH SYNOPSIS
  27 .B cat /proc/slabinfo
  28 .SH DESCRIPTION
  29 Frequently used objects in the Linux kernel
  30 (buffer heads, inodes, dentries, etc.)
  31 have their own cache.
  32 The file
  33 .I /proc/slabinfo
  34 gives statistics.
  35 For example:
  36 .LP
  37 .RS
  38 .nf
  39 % cat /proc/slabinfo
  40 slabinfo \- version: 1.1
  41 kmem_cache            60     78    100    2    2    1
  42 blkdev_requests     5120   5120     96  128  128    1
  43 mnt_cache             20     40     96    1    1    1
  44 inode_cache         7005  14792    480 1598 1849    1
  45 dentry_cache        5469   5880    128  183  196    1
  46 filp                 726    760     96   19   19    1
  47 buffer_head        67131  71240     96 1776 1781    1
  48 vm_area_struct      1204   1652     64   23   28    1
  49 \&...
  50 size-8192              1     17   8192    1   17    2
  51 size-4096             41     73   4096   41   73    1
  52 \&...
  53 .fi
  54 .RE
  55 .LP
  56 For each slab cache, the cache name, the number of currently
  57 active objects, the total number of available objects, the
  58 size of each object in bytes, the number of pages with at
  59 least one active object, the total number of allocated pages,
  60 and the number of pages per slab are given.
  61
  62 Note that because of object alignment and slab cache overhead,
  63 objects are not normally packed tightly into pages.
  64 Pages with
  65 even one in-use object are considered in-use and cannot be
  66 freed.
  67
  68 Kernels compiled with slab cache statistics will also have
  69 "(statistics)" in the first line of output, and will have 5
  70 additional columns, namely: the high water mark of active
  71 objects; the number of times objects have been allocated;
  72 the number of times the cache has grown (new pages added
  73 to this cache); the number of times the cache has been
  74 reaped (unused pages removed from this cache); and the
  75 number of times there was an error allocating new pages
  76 to this cache.
  77 If slab cache statistics are not enabled
  78 for this kernel, these columns will not be shown.
  79
  80 SMP systems will also have "(SMP)" in the first line of
  81 output, and will have two additional columns for each slab,
  82 reporting the slab allocation policy for the CPU-local
  83 cache (to reduce the need for inter-CPU synchronization
  84 when allocating objects from the cache).
  85 The first column is the per-CPU limit: the maximum number of objects that
  86 will be cached for each CPU.
  87 The second column is the
  88 batchcount: the maximum number of free objects in the
  89 global cache that will be transferred to the per-CPU cache
  90 if it is empty, or the number of objects to be returned
  91 to the global cache if the per-CPU cache is full.
  92
  93 If both slab cache statistics and SMP are defined, there
  94 will be four additional columns, reporting the per-CPU
  95 cache statistics.
  96 The first two are the per-CPU cache
  97 allocation hit and miss counts: the number of times an
  98 object was or was not available in the per-CPU cache
  99 for allocation.
 100 The next two are the per-CPU cache free
 101 hit and miss counts: the number of times a freed object
 102 could or could not fit within the per-CPU cache limit,
 103 before flushing objects to the global cache.
 104
 105 It is possible to tune the SMP per-CPU slab cache limit
 106 and batchcount via:
 107
 108 .nf
 109 echo "\fIcache_name limit batchcount\fP" > /proc/slabinfo
 110 .fi
 111 .SH VERSIONS
 112 .I /proc/slabinfo
 113 exists since Linux 2.1.23.
 114 SMP per-CPU caches exist since Linux 2.4.0-test3.
 115 .SH FILES
 116 .I <linux/slab.h>