/proc/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. 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 cur
rently 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 over
head, 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 synchroniza
tion when allocating objects from the cache). The first
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
AVAILABILITY
/proc/slabinfo exists since Linux 2.1.23. SMP per-CPU
caches exist since Linux 2.4.0-test3.
FILES
<linux/slab.h>
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