06 Sep, 2013

1 commit

• fd2ed4d25   dm: add statistics support ... Browse Code »

  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
  Signed-off-by: Mike Snitzer
  Signed-off-by: Alasdair G Kergon

  Mikulas Patocka

  2013-09-06 08:46:06 +0800