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cachetop_example.txt
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cachetop_example.txt
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# ./cachetop -h
usage: cachetop.py [-h] [interval]
show Linux page cache hit/miss statistics including read and write hit % per
processes in a UI like top.
positional arguments:
interval Interval between probes.
optional arguments:
-h, --help show this help message and exit
examples:
./cachetop # run with default option of 5 seconds delay
./cachetop 1 # print every second hit/miss stats
# ./cachetop 5
13:01:01 Buffers MB: 76 / Cached MB: 114 / Sort: HITS / Order: ascending
PID UID CMD HITS MISSES DIRTIES READ_HIT% WRITE_HIT%
1 root systemd 2 0 0 100.0% 0.0%
680 root vminfo 3 4 2 14.3% 42.9%
567 syslog rs:main Q:Reg 10 4 2 57.1% 21.4%
986 root kworker/u2:2 10 2457 4 0.2% 99.5%
988 root kworker/u2:2 10 9 4 31.6% 36.8%
877 vagrant systemd 18 4 2 72.7% 13.6%
983 root python 148 3 143 3.3% 1.3%
981 root strace 419 3 143 65.4% 0.5%
544 messageb dbus-daemon 455 371 454 0.1% 0.4%
243 root jbd2/dm-0-8 457 371 454 0.4% 0.4%
985 root (mount) 560 2457 4 18.4% 81.4%
987 root systemd-udevd 566 9 4 97.7% 1.2%
988 root systemd-cgroups 569 9 4 97.8% 1.2%
986 root modprobe 578 9 4 97.8% 1.2%
287 root systemd-journal 598 371 454 14.9% 0.3%
985 root mount 692 2457 4 21.8% 78.0%
984 vagrant find 9529 2457 4 79.5% 20.5%
Above shows the run of `find /` on a newly booted system.
Command used to generate the activity
# find /
Below shows the hit rate increases as we run find a second time and it gets it
its pages from the cache.
# ./cachetop.py
13:01:01 Buffers MB: 76 / Cached MB: 115 / Sort: HITS / Order: ascending
PID UID CMD HITS MISSES DIRTIES READ_HIT% WRITE_HIT%
544 messageb dbus-daemon 2 2 1 25.0% 50.0%
680 root vminfo 2 2 1 25.0% 50.0%
243 root jbd2/dm-0-8 3 2 1 40.0% 40.0%
1068 root python 5 0 0 100.0% 0.0%
1071 vagrant bash 350 0 0 100.0% 0.0%
1071 vagrant find 12959 0 0 100.0% 0.0%
Below shows that the dirty pages increases as a file of 80M is created running
# dd if=/dev/urandom of=/tmp/c bs=8192 count=10000
# ./cachetop.py 10
13:01:01 Buffers MB: 77 / Cached MB: 193 / Sort: HITS / Order: ascending
PID UID CMD HITS MISSES DIRTIES READ_HIT% WRITE_HIT%
544 messageb dbus-daemon 9 10 7 10.5% 15.8%
680 root vminfo 9 10 7 10.5% 15.8%
1109 root python 22 0 0 100.0% 0.0%
243 root jbd2/dm-0-8 25 10 7 51.4% 8.6%
1070 root kworker/u2:2 85 0 0 100.0% 0.0%
1110 vagrant bash 366 0 0 100.0% 0.0%
1110 vagrant dd 42183 40000 20000 27.0% 24.3%
The file copied into page cache was named /tmp/c with a size of 81920000 (81920000/4096) = 20000