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Documentation/vm/slub.txt: document slabinfo-gnuplot.sh

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Add documentation on how to use slabinfo-gnuplot.sh script.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Sergey Senozhatsky 2015-10-23 08:51:45 +09:00 • committed by Jonathan Corbet
parent 83432ef3b8
commit 05be961772
1 changed files with 59 additions and 0 deletions
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Documentation/vm/slub.txt
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@ -280,4 +280,63 @@ of other objects.
slub_debug=FZ,dentry slub_debug=FZ,dentry
Extended slabinfo mode and plotting
-----------------------------------
The slabinfo tool has a special 'extended' ('-X') mode that includes:
- Slabcache Totals
- Slabs sorted by size (up to -N <num> slabs, default 1)
- Slabs sorted by loss (up to -N <num> slabs, default 1)
Additionally, in this mode slabinfo does not dynamically scale sizes (G/M/K)
and reports everything in bytes (this functionality is also available to
other slabinfo modes via '-B' option) which makes reporting more precise and
accurate. Moreover, in some sense the `-X' mode also simplifies the analysis
of slabs' behaviour, because its output can be plotted using the
slabinfo-gnuplot.sh script. So it pushes the analysis from looking through
the numbers (tons of numbers) to something easier -- visual analysis.
To generate plots:
a) collect slabinfo extended records, for example:
while [ 1 ]; do slabinfo -X >> FOO_STATS; sleep 1; done
b) pass stats file(-s) to slabinfo-gnuplot.sh script:
slabinfo-gnuplot.sh FOO_STATS [FOO_STATS2 .. FOO_STATSN]
The slabinfo-gnuplot.sh script will pre-processes the collected records
and generates 3 png files (and 3 pre-processing cache files) per STATS
file:
- Slabcache Totals: FOO_STATS-totals.png
- Slabs sorted by size: FOO_STATS-slabs-by-size.png
- Slabs sorted by loss: FOO_STATS-slabs-by-loss.png
Another use case, when slabinfo-gnuplot can be useful, is when you need
to compare slabs' behaviour "prior to" and "after" some code modification.
To help you out there, slabinfo-gnuplot.sh script can 'merge' the
`Slabcache Totals` sections from different measurements. To visually
compare N plots:
a) Collect as many STATS1, STATS2, .. STATSN files as you need
while [ 1 ]; do slabinfo -X >> STATS<X>; sleep 1; done
b) Pre-process those STATS files
slabinfo-gnuplot.sh STATS1 STATS2 .. STATSN
c) Execute slabinfo-gnuplot.sh in '-t' mode, passing all of the
generated pre-processed *-totals
slabinfo-gnuplot.sh -t STATS1-totals STATS2-totals .. STATSN-totals
This will produce a single plot (png file).
Plots, expectedly, can be large so some fluctuations or small spikes
can go unnoticed. To deal with that, `slabinfo-gnuplot.sh' has two
options to 'zoom-in'/'zoom-out':
a) -s %d,%d overwrites the default image width and heigh
b) -r %d,%d specifies a range of samples to use (for example,
in `slabinfo -X >> FOO_STATS; sleep 1;' case, using
a "-r 40,60" range will plot only samples collected
between 40th and 60th seconds).
Christoph Lameter, May 30, 2007 Christoph Lameter, May 30, 2007
Sergey Senozhatsky, October 23, 2015