procps/man/slabtop.1
Zhao Mengmeng 25cd1bee0c slabinfo: add comment for cache_size calculation
One of our physical machine shows that the "CACHE SIZE" column
of slabtop output is extremely high, three times of the products
of objs nums and objs size. After some analysis, we found that
the order of slab, which decides "pages per slab", will shrink
when memory pressure is high and normal order allocation failed.
So we think it might help to add these comments to the man help.

Minor fix: add the "memory." back, which is lost after
"aa461df0: docs: Minor manpage fixes"

Signed-off-by: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
2023-04-25 07:19:22 +00:00

124 lines
3.6 KiB
Groff

.\"
.\" Copyright (c) 2011-2023 Craig Small <csmall@dropbear.xyz>
.\" Copyright (c) 2013-2023 Jim Warner <james.warner@comcast.net>
.\" Copyright (c) 2011-2012 Sami Kerola <kerolasa@iki.fi>
.\" Copyright (c) 2004-2006 Albert Cahalan
.\" Copyright (C) 2003 Chris Rivera
.\"
.\" This program is free software; you can redistribute it and/or modify
.\" it under the terms of the GNU Lesser General Public License as
.\" published by the Free Software Foundation; either version 2.1 of the
.\" License, or (at your option) any later version.
.\"
.\"
.TH SLABTOP "1" "2021-03-11" "procps-ng" "User Commands"
.SH NAME
slabtop \- display kernel slab cache information in real time
.SH SYNOPSIS
.B slabtop
[\fIoptions\fR]
.SH DESCRIPTION
.B slabtop
displays detailed kernel slab cache information in real time. It displays a
listing of the top caches sorted by one of the listed sort criteria. It also
displays a statistics header filled with slab layer information.
.SH OPTIONS
Normal invocation of
.B slabtop
does not require any options. The behavior, however, can be fine-tuned by
specifying one or more of the following flags:
.TP
\fB\-d\fR, \fB\-\-delay\fR=\fIN\fR
Refresh the display every
.I n
in seconds. By default,
.B slabtop
refreshes the display every three seconds. To exit the program, hit
.BR q .
This cannot be combined with the \fB-o\fR option.
.TP
\fB\-s\fR, \fB\-\-sort\fR=\fIS\fR
Sort by \fIS\fR, where \fIS\fR is one of the sort criteria.
.TP
\fB\-o\fR, \fB\-\-once\fR
Display the output once and then exit.
.TP
\fB\-V\fR, \fB\-\-version\fR
Display version information and exit.
.TP
\fB\-h\fR, \fB\-\-help\fR
Display usage information and exit.
.SH SORT CRITERIA
The following are valid sort criteria used to sort the individual slab caches
and thereby determine what are the "top" slab caches to display. The default
sort criteria is to sort by the number of objects ("o").
.PP
The sort criteria can also be changed while
.B slabtop
is running by pressing the associated character.
.TS
l l l.
\fBcharacter description header\fR
a number of active objects ACTIVE
b objects per slab OBJ/SLAB
c cache size CACHE SIZE
l number of slabs SLABS
v number of active slabs N/A
n name NAME\:
o number of objects OBJS
p pages per slab N/A
s object size OBJ SIZE
u cache utilization USE
.TE
.SH COMMANDS
.B slabtop
accepts keyboard commands from the user during use. The following are
supported. In the case of letters, both cases are accepted.
.PP
Each of the valid sort characters are also accepted, to change the sort
routine. See the section
.BR "SORT CRITERIA" .
.TP
.BR <SPACEBAR>
Refresh the screen.
.TP
.BR Q
Quit the program.
.SH FILES
.TP
.I /proc/slabinfo
slab information
.SH "SEE ALSO"
.BR free (1),
.BR ps (1),
.BR top (1),
.BR vmstat (8)
.SH NOTES
Currently,
.B slabtop
requires a 2.4 or later kernel (specifically, a version 1.1 or later
.IR /proc/slabinfo ).
Kernel 2.2 should be supported in the future.
.PP
The
.B slabtop
statistic header is tracking how many bytes of slabs are being
used and is not a measure of physical memory. The 'Slab' field in the
\fI/proc/meminfo\fR file is tracking information about used slab physical memory.
.PP
The
.B CACHE SIZE
column is not accurate, it's the upper limit of memory used by specific slab. When system
using slub (most common case) is under high memory pressure, there are slab order
fallbacks, which means "pages per slab" is not constant and may decrease.
.SH AUTHORS
Written by Chris Rivera and Robert Love.
.PP
.B slabtop
was inspired by Martin Bligh's perl script,
.BR vmtop .
.SH "REPORTING BUGS"
Please send bug reports to
.UR procps@freelists.org
.UE