SLABINFO(5) - man - phpMan

SLABINFO(5)                           Linux Programmer's Manual                          SLABINFO(5)



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 read‐
       ing 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 re‐
              filling 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 can‐
       not 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 num‐
       ber 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.

COLOPHON
       This page is part of release 5.10 of the Linux  man-pages  project.   A  description  of  the
       project,  information about reporting bugs, and the latest version of this page, can be found
       at https://www.kernel.org/doc/man-pages/.



                                             2020-11-01                                  SLABINFO(5)