man5/slabinfo.5

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  26 .TH SLABINFO 5 2017-09-15 "" "Linux Programmer's Manual"
  27 .SH NAME
  28 slabinfo \- kernel slab allocator statistics
  29 .SH SYNOPSIS
  30 .B cat /proc/slabinfo
  31 .SH DESCRIPTION
  32 Frequently used objects in the Linux kernel
  33 (buffer heads, inodes, dentries, etc.)
  34 have their own cache.
  35 The file
  36 .I /proc/slabinfo
  37 gives statistics on these caches.
  38 The following (edited) output shows an example of the
  39 contents of this file:
  40 .PP
  41 .in 0
  42 .EX
  43 $ \fBsudo cat /proc/slabinfo\fP
  44 slabinfo - version: 2.1
  45 # name    <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> ...
  46 sigqueue      100  100  160   25  1 : tunables  0  0  0 : slabdata   4   4  0
  47 sighand_cache 355   405 2112  15  8 : tunables  0  0  0 : slabdata  27  27  0
  48 kmalloc-8192   96   96  8192   4  8 : tunables  0  0  0 : slabdata  24  24  0
  49 \&...
  50 .EE
  51 .in
  52 .PP
  53 The first line of output includes a version number,
  54 which allows an application that is reading the file to handle changes
  55 in the file format.
  56 (See VERSIONS, below.)
  57 The next line lists the names of the columns in the remaining lines.
  58 .PP
  59 Each of the remaining lines displays information about a specified cache.
  60 Following the cache name,
  61 the output shown in each line shows three components for each cache:
  62 .IP * 3
  63 statistics
  64 .IP *
  65 tunables
  66 .IP *
  67 slabdata
  68 .PP
  69 The statistics are as follows:
  70 .TP
  71 .I active_objs
  72 The number of objects that are currently active (i.e., in use).
  73 .TP
  74 .I num_objs
  75 The total number of allocated objects
  76 (i.e., objects that are both in use and not in use).
  77 .TP
  78 .I objsize
  79 The size of objects in this slab, in bytes.
  80 .TP
  81 .I objperslab
  82 The number of objects stored in each slab.
  83 .TP
  84 .I pagesperslab
  85 The number of pages allocated for each slab.
  86 .PP
  87 The
  88 .I tunables
  89 entries in each line show tunable parameters for the corresponding cache.
  90 When using the default SLUB allocator, there are no tunables, the
  91 .I /proc/slabinfo
  92 file is not writable, and the value 0 is shown in these fields.
  93 When using the older SLAB allocator,
  94 the tunables for a particular cache can be set by writing
  95 lines of the following form to
  96 .IR /proc/slabinfo :
  97 .PP
  98 .in +4n
  99 .EX
 100 # \fBecho 'name limit batchcount sharedfactor' > /proc/slabinfo\fP
 101 .EE
 102 .in
 103 .PP
 104 Here,
 105 .I name
 106 is the cache name, and
 107 .IR limit ,
 108 .IR batchcount ,
 109 and
 110 .IR sharedfactor
 111 are integers defining new values for the corresponding tunables.
 112 The
 113 .I limit
 114 value should be a positive value,
 115 .I batchcount
 116 should be a positive value that is less than or equal to
 117 .IR limit ,
 118 and
 119 .I sharedfactor
 120 should be nonnegative.
 121 If any of the specified values is invalid,
 122 the cache settings are left unchanged.
 123 .PP
 124 The
 125 .I tunables
 126 entries in each line contain the following fields:
 127 .TP
 128 .I limit
 129 The maximum number of objects that will be cached.
 130 .\" https://lwn.net/Articles/56360/
 131 .\"     This is the limit on the number of free objects that can be stored
 132 .\"     in the per-CPU free list for this slab cache.
 133 .TP
 134 .I batchcount
 135 On SMP systems, this specifies the number of objects to transfer at one time
 136 when refilling the available object list.
 137 .\" https://lwn.net/Articles/56360/
 138 .\"     On SMP systems, when we refill the available object list, instead
 139 .\"     of doing one object at a time, we do batch-count objects at a time.
 140 .TP
 141 .I sharedfactor
 142 [To be documented]
 143 .\"
 144 .PP
 145 The
 146 .I slabdata
 147 entries in each line contain the following fields:
 148 .TP
 149 .I active_slabs
 150 The number of active slabs.
 151 .TP
 152 .I nums_slabs
 153 The total number of slabs.
 154 .TP
 155 .I sharedavail
 156 [To be documented]
 157 .PP
 158 Note that because of object alignment and slab cache overhead,
 159 objects are not normally packed tightly into pages.
 160 Pages with even one in-use object are considered in-use and cannot be
 161 freed.
 162 .PP
 163 Kernels configured with
 164 .B CONFIG_DEBUG_SLAB
 165 will also have additional statistics fields in each line,
 166 and the first line of the file will contain the string "(statistics)".
 167 The statistics field include : the high water mark of active
 168 objects; the number of times objects have been allocated;
 169 the number of times the cache has grown (new pages added
 170 to this cache); the number of times the cache has been
 171 reaped (unused pages removed from this cache); and the
 172 number of times there was an error allocating new pages
 173 to this cache.
 174 .\"
 175 .\" SMP systems will also have "(SMP)" in the first line of
 176 .\" output, and will have two additional columns for each slab,
 177 .\" reporting the slab allocation policy for the CPU-local
 178 .\" cache (to reduce the need for inter-CPU synchronization
 179 .\" when allocating objects from the cache).
 180 .\" The first column is the per-CPU limit: the maximum number of objects that
 181 .\" will be cached for each CPU.
 182 .\" The second column is the
 183 .\" batchcount: the maximum number of free objects in the
 184 .\" global cache that will be transferred to the per-CPU cache
 185 .\" if it is empty, or the number of objects to be returned
 186 .\" to the global cache if the per-CPU cache is full.
 187 .\"
 188 .\" If both slab cache statistics and SMP are defined, there
 189 .\" will be four additional columns, reporting the per-CPU
 190 .\" cache statistics.
 191 .\" The first two are the per-CPU cache
 192 .\" allocation hit and miss counts: the number of times an
 193 .\" object was or was not available in the per-CPU cache
 194 .\" for allocation.
 195 .\" The next two are the per-CPU cache free
 196 .\" hit and miss counts: the number of times a freed object
 197 .\" could or could not fit within the per-CPU cache limit,
 198 .\" before flushing objects to the global cache.
 199 .SH VERSIONS
 200 The
 201 .I /proc/slabinfo
 202 file first appeared in Linux 2.1.23.
 203 The file is versioned,
 204 and over time there have been a number of versions with different layouts:
 205 .TP
 206 1.0
 207 Present throughout the Linux 2.2.x kernel series.
 208 .TP
 209 1.1
 210 Present in the Linux 2.4.x kernel series.
 211 .\" First appeared in 2.4.0-test3
 212 .TP
 213 1.2
 214 A format that was briefly present in the Linux 2.5 development series.
 215 .\" from 2.5.45 to 2.5.70
 216 .TP
 217 2.0
 218 Present in Linux 2.6.x kernels up to and including Linux 2.6.9.
 219 .\" First appeared in 2.5.71
 220 .TP
 221 2.1
 222 The current format, which first appeared in Linux 2.6.10.
 223 .SH NOTES
 224 Only root can read and (if the kernel was configured with
 225 .BR CONFIG_SLAB )
 226 write the
 227 .IR /proc/slabinfo
 228 file.
 229 .PP
 230 The total amount of memory allocated to the SLAB/SLUB cache is shown in the
 231 .I Slab
 232 field of
 233 .IR /proc/meminfo .
 234 .SH SEE ALSO
 235 .BR slabtop (1)
 236 .PP
 237 The kernel source file
 238 .IR Documentation/vm/slub.txt
 239 and
 240 .IR tools/vm/slabinfo.c .