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<title>kernel.git/Documentation/device-mapper/statistics.txt, branch linux-3.19.y</title>
<subtitle>Hosts the 0x221E linux distro kernel.
</subtitle>
<id>https://git.0xinfinity.dev/distro/kernel.git/atom?h=linux-3.19.y</id>
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<updated>2013-09-06T00:46:06Z</updated>
<entry>
<title>dm: add statistics support</title>
<updated>2013-09-06T00:46:06Z</updated>
<author>
<name>Mikulas Patocka</name>
</author>
<published>2013-08-16T14:54:23Z</published>
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<id>urn:sha1:fd2ed4d252701d3bbed4cd3e3d267ad469bb832a</id>
<content type='text'>
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 &lt;mpatocka@redhat.com&gt;
Signed-off-by: Mike Snitzer &lt;snitzer@redhat.com&gt;
Signed-off-by: Alasdair G Kergon &lt;agk@redhat.com&gt;
</content>
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