slabinfo(5)

1SLABINFO(5)                Linux Programmer's Manual               SLABINFO(5)
2
3
4

NAME

6       slabinfo - kernel slab allocator statistics
7

SYNOPSIS

9       cat /proc/slabinfo
10

DESCRIPTION

12       Frequently used objects in the Linux kernel (buffer heads, inodes, den‐
13       tries, etc.)  have their own cache.  The file /proc/slabinfo gives sta‐
14       tistics  on these caches.  The following (edited) output shows an exam‐
15       ple of the contents of this file:
16
17$ sudo cat /proc/slabinfo
18slabinfo - version: 2.1
19# name    <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> ...
20sigqueue      100  100  160   25  1 : tunables  0  0  0 : slabdata   4   4  0
21sighand_cache 355   405 2112  15  8 : tunables  0  0  0 : slabdata  27  27  0
22kmalloc-8192   96   96  8192   4  8 : tunables  0  0  0 : slabdata  24  24  0
23...
24
25       The first line of output includes a version  number,  which  allows  an
26       application that is reading the file to handle changes in the file for‐
27       mat.  (See VERSIONS, below.)  The next line lists the names of the col‐
28       umns in the remaining lines.
29
30       Each  of  the  remaining  lines  displays information about a specified
31       cache.  Following the cache name, the output shown in each  line  shows
32       three components for each cache:
33
34       *  statistics
35
36       *  tunables
37
38       *  slabdata
39
40       The statistics are as follows:
41
42       active_objs
43              The number of objects that are currently active (i.e., in use).
44
45       num_objs
46              The  total  number  of allocated objects (i.e., objects that are
47              both in use and not in use).
48
49       objsize
50              The size of objects in this slab, in bytes.
51
52       objperslab
53              The number of objects stored in each slab.
54
55       pagesperslab
56              The number of pages allocated for each slab.
57
58       The tunables entries in each line show tunable parameters for the  cor‐
59       responding  cache.  When using the default SLUB allocator, there are no
60       tunables, the /proc/slabinfo file is not writable, and the value  0  is
61       shown  in  these fields.  When using the older SLAB allocator, the tun‐
62       ables for a particular cache can be set by writing lines of the follow‐
63       ing form to /proc/slabinfo:
64
65           # echo 'name limit batchcount sharedfactor' > /proc/slabinfo
66
67       Here,  name  is the cache name, and limit, batchcount, and sharedfactor
68       are integers defining new values for the corresponding  tunables.   The
69       limit value should be a positive value, batchcount should be a positive
70       value that is less than or equal to limit, and sharedfactor  should  be
71       nonnegative.  If any of the specified values is invalid, the cache set‐
72       tings are left unchanged.
73
74       The tunables entries in each line contain the following fields:
75
76       limit  The maximum number of objects that will be cached.
77
78       batchcount
79              On SMP systems, this specifies the number of objects to transfer
80              at one time when refilling the available object list.
81
82       sharedfactor
83              [To be documented]
84
85       The slabdata entries in each line contain the following fields:
86
87       active_slabs
88              The number of active slabs.
89
90       nums_slabs
91              The total number of slabs.
92
93       sharedavail
94              [To be documented]
95
96       Note  that because of object alignment and slab cache overhead, objects
97       are not normally packed tightly into pages.  Pages with even one in-use
98       object are considered in-use and cannot be freed.
99
100       Kernels  configured  with  CONFIG_DEBUG_SLAB  will also have additional
101       statistics fields in each line, and the first line  of  the  file  will
102       contain  the string "(statistics)".  The statistics field include : the
103       high water mark of active objects; the number  of  times  objects  have
104       been  allocated;  the  number  of  times the cache has grown (new pages
105       added to this cache); the number of times the  cache  has  been  reaped
106       (unused  pages  removed from this cache); and the number of times there
107       was an error allocating new pages to this cache.
108

VERSIONS

110       The /proc/slabinfo file first appeared in Linux 2.1.23.   The  file  is
111       versioned, and over time there have been a number of versions with dif‐
112       ferent layouts:
113
114       1.0    Present throughout the Linux 2.2.x kernel series.
115
116       1.1    Present in the Linux 2.4.x kernel series.
117
118       1.2    A format that was briefly present in the Linux  2.5  development
119              series.
120
121       2.0    Present in Linux 2.6.x kernels up to and including Linux 2.6.9.
122
123       2.1    The current format, which first appeared in Linux 2.6.10.
124

NOTES

126       Only  root can read and (if the kernel was configured with CONFIG_SLAB)
127       write the /proc/slabinfo file.
128
129       The total amount of memory allocated to the SLAB/SLUB cache is shown in
130       the Slab field of /proc/meminfo.
131

COLOPHON

139       This page is part of release 5.07 of the Linux  man-pages  project.   A
140       description  of  the project, information about reporting bugs, and the
141       latest    version    of    this    page,    can     be     found     at
142       https://www.kernel.org/doc/man-pages/.
143
144
145
146                                  2017-09-15                       SLABINFO(5)

NAME

SYNOPSIS

DESCRIPTION

VERSIONS

NOTES

SEE ALSO

COLOPHON