25cd1bee0c
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>
124 lines
3.6 KiB
Groff
124 lines
3.6 KiB
Groff
.\"
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.\" Copyright (c) 2011-2023 Craig Small <csmall@dropbear.xyz>
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.\" Copyright (c) 2013-2023 Jim Warner <james.warner@comcast.net>
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.\" Copyright (c) 2011-2012 Sami Kerola <kerolasa@iki.fi>
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.\" Copyright (c) 2004-2006 Albert Cahalan
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.\" Copyright (C) 2003 Chris Rivera
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.\"
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.\" This program is free software; you can redistribute it and/or modify
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.\" it under the terms of the GNU Lesser General Public License as
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.\" published by the Free Software Foundation; either version 2.1 of the
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.\" License, or (at your option) any later version.
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.\"
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.\"
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.TH SLABTOP "1" "2021-03-11" "procps-ng" "User Commands"
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.SH NAME
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slabtop \- display kernel slab cache information in real time
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.SH SYNOPSIS
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.B slabtop
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[\fIoptions\fR]
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.SH DESCRIPTION
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.B slabtop
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displays detailed kernel slab cache information in real time. It displays a
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listing of the top caches sorted by one of the listed sort criteria. It also
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displays a statistics header filled with slab layer information.
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.SH OPTIONS
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Normal invocation of
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.B slabtop
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does not require any options. The behavior, however, can be fine-tuned by
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specifying one or more of the following flags:
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.TP
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\fB\-d\fR, \fB\-\-delay\fR=\fIN\fR
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Refresh the display every
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.I n
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in seconds. By default,
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.B slabtop
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refreshes the display every three seconds. To exit the program, hit
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.BR q .
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This cannot be combined with the \fB-o\fR option.
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.TP
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\fB\-s\fR, \fB\-\-sort\fR=\fIS\fR
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Sort by \fIS\fR, where \fIS\fR is one of the sort criteria.
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.TP
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\fB\-o\fR, \fB\-\-once\fR
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Display the output once and then exit.
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.TP
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\fB\-V\fR, \fB\-\-version\fR
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Display version information and exit.
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.TP
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\fB\-h\fR, \fB\-\-help\fR
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Display usage information and exit.
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.SH SORT CRITERIA
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The following are valid sort criteria used to sort the individual slab caches
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and thereby determine what are the "top" slab caches to display. The default
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sort criteria is to sort by the number of objects ("o").
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.PP
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The sort criteria can also be changed while
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.B slabtop
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is running by pressing the associated character.
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.TS
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l l l.
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\fBcharacter description header\fR
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a number of active objects ACTIVE
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b objects per slab OBJ/SLAB
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c cache size CACHE SIZE
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l number of slabs SLABS
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v number of active slabs N/A
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n name NAME\:
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o number of objects OBJS
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p pages per slab N/A
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s object size OBJ SIZE
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u cache utilization USE
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.TE
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.SH COMMANDS
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.B slabtop
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accepts keyboard commands from the user during use. The following are
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supported. In the case of letters, both cases are accepted.
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.PP
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Each of the valid sort characters are also accepted, to change the sort
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routine. See the section
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.BR "SORT CRITERIA" .
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.TP
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.BR <SPACEBAR>
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Refresh the screen.
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.TP
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.BR Q
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Quit the program.
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.SH FILES
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.TP
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.I /proc/slabinfo
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slab information
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.SH "SEE ALSO"
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.BR free (1),
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.BR ps (1),
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.BR top (1),
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.BR vmstat (8)
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.SH NOTES
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Currently,
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.B slabtop
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requires a 2.4 or later kernel (specifically, a version 1.1 or later
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.IR /proc/slabinfo ).
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Kernel 2.2 should be supported in the future.
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.PP
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The
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.B slabtop
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statistic header is tracking how many bytes of slabs are being
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used and is not a measure of physical memory. The 'Slab' field in the
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\fI/proc/meminfo\fR file is tracking information about used slab physical memory.
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.PP
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The
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.B CACHE SIZE
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column is not accurate, it's the upper limit of memory used by specific slab. When system
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using slub (most common case) is under high memory pressure, there are slab order
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fallbacks, which means "pages per slab" is not constant and may decrease.
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.SH AUTHORS
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Written by Chris Rivera and Robert Love.
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.PP
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.B slabtop
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was inspired by Martin Bligh's perl script,
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.BR vmtop .
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.SH "REPORTING BUGS"
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Please send bug reports to
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.UR procps@freelists.org
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.UE
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