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 reading 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 refilling 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 consid‐
       ered in-use and cannot 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 "(sta‐
       tistics)".  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 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.

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.

                                                                               2021-03-22                                                                    SLABINFO(5)