1# ./cachetop -h 2usage: cachetop.py [-h] [interval] 3 4show Linux page cache hit/miss statistics including read and write hit % per 5processes in a UI like top. 6 7positional arguments: 8 interval Interval between probes. 9 10optional arguments: 11 -h, --help show this help message and exit 12 13examples: 14 ./cachetop # run with default option of 5 seconds delay 15 ./cachetop 1 # print every second hit/miss stats 16 17# ./cachetop 5 1813:01:01 Buffers MB: 76 / Cached MB: 114 / Sort: HITS / Order: ascending 19PID UID CMD HITS MISSES DIRTIES READ_HIT% WRITE_HIT% 20 1 root systemd 2 0 0 100.0% 0.0% 21 680 root vminfo 3 4 2 14.3% 42.9% 22 567 syslog rs:main Q:Reg 10 4 2 57.1% 21.4% 23 986 root kworker/u2:2 10 2457 4 0.2% 99.5% 24 988 root kworker/u2:2 10 9 4 31.6% 36.8% 25 877 vagrant systemd 18 4 2 72.7% 13.6% 26 983 root python 148 3 143 3.3% 1.3% 27 981 root strace 419 3 143 65.4% 0.5% 28 544 messageb dbus-daemon 455 371 454 0.1% 0.4% 29 243 root jbd2/dm-0-8 457 371 454 0.4% 0.4% 30 985 root (mount) 560 2457 4 18.4% 81.4% 31 987 root systemd-udevd 566 9 4 97.7% 1.2% 32 988 root systemd-cgroups 569 9 4 97.8% 1.2% 33 986 root modprobe 578 9 4 97.8% 1.2% 34 287 root systemd-journal 598 371 454 14.9% 0.3% 35 985 root mount 692 2457 4 21.8% 78.0% 36 984 vagrant find 9529 2457 4 79.5% 20.5% 37 38Above shows the run of `find /` on a newly booted system. 39 40Command used to generate the activity 41# find / 42 43Below shows the hit rate increases as we run find a second time and it gets it 44its pages from the cache. 45# ./cachetop.py 4613:01:01 Buffers MB: 76 / Cached MB: 115 / Sort: HITS / Order: ascending 47PID UID CMD HITS MISSES DIRTIES READ_HIT% WRITE_HIT% 48 544 messageb dbus-daemon 2 2 1 25.0% 50.0% 49 680 root vminfo 2 2 1 25.0% 50.0% 50 243 root jbd2/dm-0-8 3 2 1 40.0% 40.0% 51 1068 root python 5 0 0 100.0% 0.0% 52 1071 vagrant bash 350 0 0 100.0% 0.0% 53 1071 vagrant find 12959 0 0 100.0% 0.0% 54 55 56Below shows that the dirty pages increases as a file of 80M is created running 57# dd if=/dev/urandom of=/tmp/c bs=8192 count=10000 58 59# ./cachetop.py 10 6013:01:01 Buffers MB: 77 / Cached MB: 193 / Sort: HITS / Order: ascending 61PID UID CMD HITS MISSES DIRTIES READ_HIT% WRITE_HIT% 62 544 messageb dbus-daemon 9 10 7 10.5% 15.8% 63 680 root vminfo 9 10 7 10.5% 15.8% 64 1109 root python 22 0 0 100.0% 0.0% 65 243 root jbd2/dm-0-8 25 10 7 51.4% 8.6% 66 1070 root kworker/u2:2 85 0 0 100.0% 0.0% 67 1110 vagrant bash 366 0 0 100.0% 0.0% 68 1110 vagrant dd 42183 40000 20000 27.0% 24.3% 69 70The file copied into page cache was named /tmp/c with a size of 81920000 (81920000/4096) = 20000 71