• Mikulas Patocka's avatar
    dm: add statistics support · fd2ed4d2
    Mikulas Patocka authored
    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: default avatarMikulas Patocka <mpatocka@redhat.com>
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
    Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
    fd2ed4d2
dm-stats.h 904 Bytes