# ./cachestat -h
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USAGE: ./cachestat [-T] [ interval [count] ]
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show Linux page cache hit/miss statistics including read and write hit %
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optional arguments:
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-T include timestamp on output
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examples:
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./cachestat # run with default option of 5 seconds delay
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./cachestat -T # run with default option of 5 seconds delay with timestamps
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./cachestat 1 # print every second hit/miss stats
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./cachestat -T 1 # include timestamps with one second samples
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./cachestat 1 5 # run with interval of one second for five iterations
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./cachestat -T 1 5 # include timestamps with interval of one second for five iterations
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Following commands show a 2GB file being read into the page cache.
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Command used to generate activity:
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# dd if=/root/tmpfile of=/dev/null bs=8192
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Output from cachestat running simultatenously:
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# ./tools/cachestat.py 1
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TOTAL MISSES HITS DIRTIES BUFFERS_MB CACHED_MB
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1 0 1 0 8 283
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0 0 0 0 8 283
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0 0 0 2 8 283
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0 0 0 0 8 283
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10009 9173 836 2 9 369
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152032 152032 0 0 9 1028
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157408 157405 3 0 9 1707
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150432 150432 0 0 9 2331
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0 0 0 0 9 2331
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1 1 0 1 9 2331
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0 0 0 0 9 2331
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0 0 0 0 9 2331
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0 0 0 0 9 2331
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The misses counter reflects a 2GB file being read and almost everything being
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a page cache miss.
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Below shows an example of a new 100MB file added to page cache, by using
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the command: dd if=/dev/zero of=/root/tmpfile2 bs=4k count=$((256*100))
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# ./tools/cachestat.py 1
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TOTAL MISSES HITS DIRTIES BUFFERS_MB CACHED_MB
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0 0 0 0 15 2440
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0 0 0 0 15 2440
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0 0 0 0 15 2440
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1758 0 1758 25603 15 2540
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0 0 0 0 15 2540
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0 0 0 0 15 2541
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~25600 pages are being dirtied (writes) which corresponds to the 100MB file
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added to the page cache.
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