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