# slabinfo

## 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 considered 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 "(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 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_.
    


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