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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2017-01-25 15:03:46 +1300 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2017-04-24 11:37:23 +0200 |
| commit | 27e78df197ff5eadf07e3167eb40d866899124b0 (patch) | |
| tree | 85f01cd2eed5711ed9fd8b3f5157cdf527c07ddd /man5 | |
| parent | 2c43dda3919959c223e2677a2360e47db7aa4049 (diff) | |
| download | man-pages-27e78df197ff5eadf07e3167eb40d866899124b0.tar.gz | |
slabinfo.5: Rewrite to try to bring the content close to current reality
There's still gaps to fill in, but the existing page
was in any case hugely out of date.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Diffstat (limited to 'man5')
| -rw-r--r-- | man5/slabinfo.5 | 234 |
1 files changed, 156 insertions, 78 deletions
diff --git a/man5/slabinfo.5 b/man5/slabinfo.5 index 0bd48f8ae8..0a836487d0 100644 --- a/man5/slabinfo.5 +++ b/man5/slabinfo.5 @@ -1,4 +1,5 @@ .\" Copyright (c) 2001 Andreas Dilger (adilger@turbolinux.com) +.\" and Copyright (c) 2017 Michael kerrisk <mtk.manpages@gmail.com> .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this @@ -22,15 +23,6 @@ .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" -.\" FIXME Over time, the slabinfo format has gone through -.\" version changes. These should be documented: -.\" -.\" slabinfo 1.0 - Linux 2.2 (precisely: 2.1.23) -.\" slabinfo 1.1 - Linux 2.4 (precisely: 2.4.0-test3) -.\" slabinfo 1.2 - Linux 2.5.45 -.\" slabinfo 2.0 - Linux 2.6 (precisely: 2.5.71) -.\" slabinfo 2.1 - Linux 2.6.10 -.\" .TH SLABINFO 5 2017-03-13 "" "Linux Programmer's Manual" .SH NAME slabinfo \- kernel slab allocator statistics @@ -42,95 +34,181 @@ Frequently used objects in the Linux kernel have their own cache. The file .I /proc/slabinfo -gives statistics. -For example: +gives statistics on these caches. +The following (edited) output shows an example of the +contents of this file: .LP -.in +4n +.in 0 .nf -% 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 +$ \fBsudo cat /proc/slabinfo\fP +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 \&... .fi .in .LP -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. +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: +.IP * 3 +statistics +.IP * +tunables +.IP * +slabdata +.PP +The statistics are as follows: +.TP +.I active_objs +The number of objects that are currently active (i.e., in use). +.TP +.I num_objs +The total number of allocated objects +(i.e., objects that are both in use and not in use). +.TP +.I objsize +The size of objects in this slab, in bytes. +.TP +.I objperslab +The number of objects stored in each slab. +.TP +.I pagesperslab +The number of pages allocated for each slab. +.PP +The +.I tunables +entries in each line show tunable parameters for the corresponding cache. +When using the default SLUB allocator, there are no tunables, the +.I /proc/slabinfo +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 +.IR /proc/slabinfo : + # \fBecho 'name limit batchcount sharedfactor' > /proc/slabinfo\fP + +Here, +.I name +is the cache name, and +.IR limit , +.IR batchcount , +and +.IR sharedfactor +are integers defining new values for the corresponding tunables. + +The +.I tunables +entries in each line contain the following fields: +.TP +.I limit +The maximum number of objects that will be cached. +.\" https://lwn.net/Articles/56360/ +.\" This is the limit on the number of free objects that can be stored +.\" in the per-CPU free list for this slab cache. +.TP +.I batchcount +[To be documented] +.\" https://lwn.net/Articles/56360/ +.\" On SMP systems, when we refill the available object list, instead +.\" of doing one object at a time, we do batch-count objects at a time. +.TP +.I sharedfactor +[To be documented] +.\" +.PP +The +.I slabdata +entries in each line contain the following fields: +.TP +.I active_slabs +The number of active slabs. +.TP +.I nums_slabs +The total number of slabs. +.TP +.I sharedavail +[To be documented] +.PP 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 +Kernels configured with +.B 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. -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: - -.in +4n -.nf -echo "\fIcache_name limit batchcount\fP" > /proc/slabinfo -.fi -.in -.SH FILES -.I <linux/slab.h> +.\" +.\" 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. .SH VERSIONS +The .I /proc/slabinfo -exists since Linux 2.1.23. -SMP per-CPU caches exist since Linux 2.4.0-test3. +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: +.TP +1.0 +Present throughout the Linux 2.2.x kernel series. +.TP +1.1 +Present in the Linux 2.4.x kernel series. +.\" First appeared in 2.4.0-test3 +.TP +1.2 +A format that was briefly present in the Linux 2.5 development series. +.\" from 2.5.45 to 2.5.70 +.TP +2.0 +Present in Linux 2.6.x kernels up to and including Linux 2.6.9. +.\" First appeared in 2.5.71 +.TP +2.1 +The current format, which first appeared in Linux 2.6.10. .SH NOTES -Since Linux 2.6.16 the file -.I /proc/slabinfo -is present only if the -.B CONFIG_SLAB -kernel configuration option is enabled. +Only root can read and (if the kernel was configured with +.BR CONFIG_SLAB ) +write the +.IR /proc/slabinfo +file. .SH SEE ALSO .BR slabtop (1) |