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cachestat_example.txt
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cachestat_example.txt
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# ./cachestat -h
USAGE: ./cachestat [-T] [ interval [count] ]
show Linux page cache hit/miss statistics including read and write hit %
optional arguments:
-T include timestamp on output
examples:
./cachestat # run with default option of 5 seconds delay
./cachestat -T # run with default option of 5 seconds delay with timestamps
./cachestat 1 # print every second hit/miss stats
./cachestat -T 1 # include timestamps with one second samples
./cachestat 1 5 # run with interval of one second for five iterations
./cachestat -T 1 5 # include timestamps with interval of one second for five iterations
# ./cachestat 1
HITS MISSES DIRTIES READ_HIT% WRITE_HIT% BUFFERS_MB CACHED_MB
0 58 0 0.0% 100.0% 0 11334
146113 0 0 100.0% 0.0% 0 11334
244143 0 0 100.0% 0.0% 0 11334
216833 0 0 100.0% 0.0% 0 11334
248209 0 0 100.0% 0.0% 0 11334
205825 0 0 100.0% 0.0% 0 11334
286654 0 0 100.0% 0.0% 0 11334
275850 0 0 100.0% 0.0% 0 11334
272883 0 0 100.0% 0.0% 0 11334
261633 0 0 100.0% 0.0% 0 11334
252826 0 0 100.0% 0.0% 0 11334
235253 70 3 100.0% 0.0% 0 11335
204946 0 0 100.0% 0.0% 0 11335
0 0 0 0.0% 0.0% 0 11335
0 0 0 0.0% 0.0% 0 11335
0 0 0 0.0% 0.0% 0 11335
Above shows the reading of a 12GB file already cached in the OS page cache and again below with timestamps.
# ./cachestat -T 1
TIME HITS MISSES DIRTIES READ_HIT% WRITE_HIT% BUFFERS_MB CACHED_MB
16:07:10 0 0 0 0.0% 0.0% 0 11336
16:07:11 0 0 0 0.0% 0.0% 0 11336
16:07:12 117849 0 0 100.0% 0.0% 0 11336
16:07:13 212558 0 0 100.0% 0.0% 0 11336
16:07:14 302559 1 0 100.0% 0.0% 0 11336
16:07:15 309230 0 0 100.0% 0.0% 0 11336
16:07:16 305701 0 0 100.0% 0.0% 0 11336
16:07:17 312754 0 0 100.0% 0.0% 0 11336
16:07:18 308406 0 0 100.0% 0.0% 0 11336
16:07:19 298185 0 0 100.0% 0.0% 0 11336
16:07:20 236128 0 0 100.0% 0.0% 0 11336
16:07:21 257616 0 0 100.0% 0.0% 0 11336
16:07:22 179792 0 0 100.0% 0.0% 0 11336
Command used to generate the activity
# dd if=/root/mnt2/testfile of=/dev/null bs=8192
1442795+0 records in
1442795+0 records out
11819376640 bytes (12 GB) copied, 3.9301 s, 3.0 GB/s
Below shows the dirty ratio increasing as we add a file to the page cache
# ./cachestat.py
HITS MISSES DIRTIES READ_HIT% WRITE_HIT% BUFFERS_MB CACHED_MB
1074 44 13 94.9% 2.9% 1 223
2195 170 8 92.5% 6.8% 1 143
182 53 56 53.6% 1.3% 1 143
62480 40960 20480 40.6% 19.8% 1 223
7 2 5 22.2% 22.2% 1 223
348 0 0 100.0% 0.0% 1 223
0 0 0 0.0% 0.0% 1 223
0 0 0 0.0% 0.0% 1 223
0 0 0 0.0% 0.0% 1 223
0 0 0 0.0% 0.0% 1 223
The file copied into page cache was named 80m with a size of 83886080 (83886080/4096) = 20480, this matches what we see under dirties