NAME

       cachestat - Statistics for linux page cache hit/miss ratios. Uses Linux eBPF/bcc.

SYNOPSIS

       cachestat [-T] [interval [count]]

DESCRIPTION

       This  traces  four  kernel  functions  and  prints  per-second  summaries. This can be useful for general
       workload characterization, and looking for patterns in operation usage over time.

       This works by tracing kernel page cache functions using dynamic tracing, and will need updating to  match
       any changes to these functions. Edit the script to customize which functions are traced.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

       CONFIG_BPF and bcc.

EXAMPLES

       Print summaries every second:
              # cachestat

       Print summaries every second with timestamp:
              # cachestat -T

       Print output every five seconds, three times:
              # cachestat 5 3

       Print output with timestamp every five seconds, three times:
              # cachestat -T 5 3

FIELDS

       TIME   Timestamp.

       HITS   Number of page cache hits.

       MISSES Number of page cache misses.

       DIRTIES
              Number of dirty pages added to the page cache.

       HITRATIO
              The hit ratio as a percentage.

       READ_HIT%
              Read hit percent of page cache usage.

       WRITE_HIT%
              Write hit percent of page cache usage.

       BUFFERS_MB
              Buffers size taken from /proc/meminfo.

       CACHED_MB
              Cached amount of data in current page cache taken from /proc/meminfo.

OVERHEAD

       This  traces various kernel page cache functions and maintains in-kernel counts, which are asynchronously
       copied to user-space. While the rate of operations can be very high (>1G/sec)  we  can  have  up  to  34%
       overhead, this is still a relatively efficient way to trace these events, and so the overhead is expected
       to be small for normal workloads.  Measure in a test environment.

SOURCE

       This is from bcc.

              https://github.com/iovisor/bcc

       Also  look  in  the bcc distribution for a companion _examples.txt file containing example usage, output,
       and commentary for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Allan McAleavy

SEE ALSO

       https://github.com/brendangregg/perf-tools/blob/master/fs/cachestat

USER COMMANDS                                      2016-01-30                                       cachestat(8)