1Demonstrations of cachestat, the Linux eBPF/bcc version. 2 3 4cachestat shows hits and misses to the file system page cache. For example: 5 6# cachestat 7 HITS MISSES DIRTIES HITRATIO BUFFERS_MB CACHED_MB 8 1132 0 4 100.00% 277 4367 9 161 0 36 100.00% 277 4372 10 16 0 28 100.00% 277 4372 11 17154 13750 15 55.51% 277 4422 12 19 0 1 100.00% 277 4422 13 83 0 83 100.00% 277 4421 14 16 0 1 100.00% 277 4423 15^C 0 -19 360 0.00% 277 4423 16Detaching... 17 18While tracing, there was a burst of misses in the fourth second, bringing 19the hit ration down to 55%. 20 21 22This shows a 1 Gbyte uncached file that is read twice: 23 24(root) ~ # ./cachestat.py 25 HITS MISSES DIRTIES HITRATIO BUFFERS_MB CACHED_MB 26 1 0 0 100.00% 5 191 27 198 12136 0 1.61% 5 238 28 1 11007 3 0.01% 5 281 29 0 6384 0 0.00% 5 306 30 1 14464 0 0.01% 5 363 31 0 11776 0 0.00% 5 409 32 1 11712 0 0.01% 5 454 33 32 13184 0 0.24% 5 506 34 0 11232 0 0.00% 5 550 35 1 13056 0 0.01% 5 601 36 16 14720 0 0.11% 5 658 37 33 9920 0 0.33% 5 697 38 0 13248 0 0.00% 5 749 39 4 14144 0 0.03% 5 804 40 0 9728 0 0.00% 5 842 41 1 10816 0 0.01% 5 885 42 808 13504 1 5.65% 5 938 43 0 11409 0 0.00% 5 982 44 0 11520 0 0.00% 5 1027 45 0 15616 0 0.00% 5 1088 46 1 9792 0 0.01% 5 1126 47 0 8256 0 0.00% 5 1158 48 1 9600 0 0.01% 5 1196 49 599 4804 0 11.09% 5 1215 50 1 0 0 100.00% 5 1215 51 0 0 0 0.00% 5 1215 52 3 1 0 75.00% 5 1215 53 79536 34 0 99.96% 5 1215 54 87693 274 4 99.69% 6 1214 55 89018 3546 0 96.17% 7 1227 56 33531 201 4 99.40% 7 1228 57 22 44 0 33.33% 8 1228 58 0 0 0 0.00% 8 1228 59 73 21 2 77.66% 8 1228 60 61It took 24 seconds to read the 1 Gbyte file the first time, shown in the output 62by the high MISSES rate and low HITRATIO. The second time it took 4 seconds, 63and the HITRATIO was around 99%. 64 65 66This output shows a 1 Gbyte file being created and added to the page cache: 67 68(root) ~ # ./cachestat.py 69 HITS MISSES DIRTIES HITRATIO BUFFERS_MB CACHED_MB 70 1 0 0 100.00% 8 209 71 0 0 165584 0.00% 8 856 72 0 0 96505 0.00% 8 1233 73 0 0 0 0.00% 8 1233 74 75Note the high rate of DIRTIES, and the CACHED_MB size increases by 1024 Mbytes. 76 77 78USAGE message: 79 80# cachestat -h 81usage: cachestat.py [-h] [-T] [interval] [count] 82 83Count cache kernel function calls 84 85positional arguments: 86 interval output interval, in seconds 87 count number of outputs 88 89optional arguments: 90 -h, --help show this help message and exit 91 -T, --timestamp include timestamp on output 92