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| author | Mikulas Patocka <mpatocka@redhat.com> | 2013-08-16 10:54:23 -0400 |
|---|---|---|
| committer | Mike Snitzer <snitzer@redhat.com> | 2013-09-05 20:46:06 -0400 |
| commit | fd2ed4d252701d3bbed4cd3e3d267ad469bb832a (patch) | |
| tree | 264ff043406894bd447eb6e9976b9a2b4d69bd9f /Documentation/device-mapper | |
| parent | 94563badaf41f9291ff0bad94a443a4319b9e312 (diff) | |
dm: add statistics support
Support the collection of I/O statistics on user-defined regions of
a DM device. If no regions are defined no statistics are collected so
there isn't any performance impact. Only bio-based DM devices are
currently supported.
Each user-defined region specifies a starting sector, length and step.
Individual statistics will be collected for each step-sized area within
the range specified.
The I/O statistics counters for each step-sized area of a region are
in the same format as /sys/block/*/stat or /proc/diskstats but extra
counters (12 and 13) are provided: total time spent reading and
writing in milliseconds. All these counters may be accessed by sending
the @stats_print message to the appropriate DM device via dmsetup.
The creation of DM statistics will allocate memory via kmalloc or
fallback to using vmalloc space. At most, 1/4 of the overall system
memory may be allocated by DM statistics. The admin can see how much
memory is used by reading
/sys/module/dm_mod/parameters/stats_current_allocated_bytes
See Documentation/device-mapper/statistics.txt for more details.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'Documentation/device-mapper')