/proc/slabinfo — Kernel slab allocator statistics
cat /proc/slabinfo
Frequently used objects in the Linux kernel (buffer heads,
inodes, dentries, etc.) have their own cache. The file
/proc/slabinfo gives
statistics. For example:
% cat /proc/slabinfo slabinfo − version: 1.1 kmem_cache 60 78 100 2 2 1 blkdev_requests 5120 5120 96 128 128 1 mnt_cache 20 40 96 1 1 1 inode_cache 7005 14792 480 1598 1849 1 dentry_cache 5469 5880 128 183 196 1 filp 726 760 96 19 19 1 buffer_head 67131 71240 96 1776 1781 1 vm_area_struct 1204 1652 64 23 28 1 ... size-8192 1 17 8192 1 17 2 size-4096 41 73 4096 41 73 1 ...
For each slab cache, the cache name, the number of currently active objects, the total number of available objects, the size of each object in bytes, the number of pages with at least one active object, the total number of allocated pages, and the number of pages per slab are given.
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 compiled with slab cache statistics will also have "(statistics)" in the first line of output, and will have 5 additional columns, namely: 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. If slab cache statistics are not enabled for this kernel, these columns will not be shown.
SMP systems will also have "(SMP)" in the first line of output, and will have two additional columns for each slab, reporting the slab allocation policy for the CPU-local cache (to reduce the need for inter-CPU synchronization when allocating objects from the cache). The first column is the per-CPU limit: the maximum number of objects that will be cached for each CPU. The second column is the batchcount: the maximum number of free objects in the global cache that will be transferred to the per-CPU cache if it is empty, or the number of objects to be returned to the global cache if the per-CPU cache is full.
If both slab cache statistics and SMP are defined, there will be four additional columns, reporting the per-CPU cache statistics. The first two are the per-CPU cache allocation hit and miss counts: the number of times an object was or was not available in the per-CPU cache for allocation. The next two are the per-CPU cache free hit and miss counts: the number of times a freed object could or could not fit within the per-CPU cache limit, before flushing objects to the global cache.
It is possible to tune the SMP per-CPU slab cache limit and batchcount via:
echo "cache_name limit batchcount" > /proc/slabinfo
/proc/slabinfo exists since
Linux 2.1.23. SMP per-CPU caches exist since Linux
2.4.0-test3.
Since Linux 2.6.16 the file /proc/slabinfo is only present if the
CONFIG_SLAB kernel
configuration option is enabled.
This page is part of release 2.79 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man-pages/.
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Copyright (c) 2001 Andreas Dilger (adilgerturbolinux.com) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. |