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>

Documentation/device-mapper/statistics.txt

@@ -0,0 +1,186 @@
+DM statistics
+=============
+
+Device Mapper supports 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 (see:
+Documentation/iostats.txt). But two 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.
+
+Each region has a corresponding unique identifier, which we call a
+region_id, that is assigned when the region is created. The region_id
+must be supplied when querying statistics about the region, deleting the
+region, etc. Unique region_ids enable multiple userspace programs to
+request and process statistics for the same DM device without stepping
+on each other's data.
+
+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
+
+Messages
+========
+
+ @stats_create <range> <step> [<program_id> [<aux_data>]]
+
+ Create a new region and return the region_id.
+
+ <range>
+ "-" - whole device
+ "<start_sector>+<length>" - a range of <length> 512-byte sectors
+ starting with <start_sector>.
+
+ <step>
+ "<area_size>" - the range is subdivided into areas each containing
+ <area_size> sectors.
+ "/<number_of_areas>" - the range is subdivided into the specified
+ number of areas.
+
+ <program_id>
+ An optional parameter. A name that uniquely identifies
+ the userspace owner of the range. This groups ranges together
+ so that userspace programs can identify the ranges they
+ created and ignore those created by others.
+ The kernel returns this string back in the output of
+ @stats_list message, but it doesn't use it for anything else.
+
+ <aux_data>
+ An optional parameter. A word that provides auxiliary data
+ that is useful to the client program that created the range.
+ The kernel returns this string back in the output of
+ @stats_list message, but it doesn't use this value for anything.
+
+ @stats_delete <region_id>
+
+ Delete the region with the specified id.
+
+ <region_id>
+ region_id returned from @stats_create
+
+ @stats_clear <region_id>
+
+ Clear all the counters except the in-flight i/o counters.
+
+ <region_id>
+ region_id returned from @stats_create
+
+ @stats_list [<program_id>]
+
+ List all regions registered with @stats_create.
+
+ <program_id>
+ An optional parameter.
+ If this parameter is specified, only matching regions
+ are returned.
+ If it is not specified, all regions are returned.
+
+ Output format:
+ <region_id>: <start_sector>+<length> <step> <program_id> <aux_data>
+
+ @stats_print <region_id> [<starting_line> <number_of_lines>]
+
+ Print counters for each step-sized area of a region.
+
+ <region_id>
+ region_id returned from @stats_create
+
+ <starting_line>
+ The index of the starting line in the output.
+ If omitted, all lines are returned.
+
+ <number_of_lines>
+ The number of lines to include in the output.
+ If omitted, all lines are returned.
+
+ Output format for each step-sized area of a region:
+
+ <start_sector>+<length> counters
+
+ The first 11 counters have the same meaning as
+ /sys/block/*/stat or /proc/diskstats.
+
+ Please refer to Documentation/iostats.txt for details.
+
+ 1. the number of reads completed
+ 2. the number of reads merged
+ 3. the number of sectors read
+ 4. the number of milliseconds spent reading
+ 5. the number of writes completed
+ 6. the number of writes merged
+ 7. the number of sectors written
+ 8. the number of milliseconds spent writing
+ 9. the number of I/Os currently in progress
+ 10. the number of milliseconds spent doing I/Os
+ 11. the weighted number of milliseconds spent doing I/Os
+
+ Additional counters:
+ 12. the total time spent reading in milliseconds
+ 13. the total time spent writing in milliseconds
+
+ @stats_print_clear <region_id> [<starting_line> <number_of_lines>]
+
+ Atomically print and then clear all the counters except the
+ in-flight i/o counters. Useful when the client consuming the
+ statistics does not want to lose any statistics (those updated
+ between printing and clearing).
+
+ <region_id>
+ region_id returned from @stats_create
+
+ <starting_line>
+ The index of the starting line in the output.
+ If omitted, all lines are printed and then cleared.
+
+ <number_of_lines>
+ The number of lines to process.
+ If omitted, all lines are printed and then cleared.
+
+ @stats_set_aux <region_id> <aux_data>
+
+ Store auxiliary data aux_data for the specified region.
+
+ <region_id>
+ region_id returned from @stats_create
+
+ <aux_data>
+ The string that identifies data which is useful to the client
+ program that created the range. The kernel returns this
+ string back in the output of @stats_list message, but it
+ doesn't use this value for anything.
+
+Examples
+========
+
+Subdivide the DM device 'vol' into 100 pieces and start collecting
+statistics on them:
+
+ dmsetup message vol 0 @stats_create - /100
+
+Set the auxillary data string to "foo bar baz" (the escape for each
+space must also be escaped, otherwise the shell will consume them):
+
+ dmsetup message vol 0 @stats_set_aux 0 foo\\ bar\\ baz
+
+List the statistics:
+
+ dmsetup message vol 0 @stats_list
+
+Print the statistics:
+
+ dmsetup message vol 0 @stats_print 0
+
+Delete the statistics:
+
+ dmsetup message vol 0 @stats_delete 0

drivers/md/Makefile

@@ -3,7 +3,7 @@
 #
 
 dm-mod-y += dm.o dm-table.o dm-target.o dm-linear.o dm-stripe.o \
- dm-ioctl.o dm-io.o dm-kcopyd.o dm-sysfs.o
+ dm-ioctl.o dm-io.o dm-kcopyd.o dm-sysfs.o dm-stats.o
 dm-multipath-y += dm-path-selector.o dm-mpath.o
 dm-snapshot-y += dm-snap.o dm-exception-store.o dm-snap-transient.o \
  dm-snap-persistent.o

drivers/md/dm-ioctl.c

@@ -1455,20 +1455,26 @@ static int table_status(struct dm_ioctl *param, size_t param_size)
  return 0;
 }
 
-static bool buffer_test_overflow(char *result, unsigned maxlen)
-{
- return !maxlen || strlen(result) + 1 >= maxlen;
-}
-
 /*
- * Process device-mapper dependent messages.
+ * Process device-mapper dependent messages. Messages prefixed with '@'
+ * are processed by the DM core. All others are delivered to the target.
  * Returns a number <= 1 if message was processed by device mapper.
  * Returns 2 if message should be delivered to the target.
  */
 static int message_for_md(struct mapped_device *md, unsigned argc, char **argv,
  char *result, unsigned maxlen)
 {
- return 2;
+ int r;
+
+ if (**argv != '@')
+ return 2; /* no '@' prefix, deliver to target */
+
+ r = dm_stats_message(md, argc, argv, result, maxlen);
+ if (r < 2)
+ return r;
+
+ DMERR("Unsupported message sent to DM core: %s", argv[0]);
+ return -EINVAL;
 }
 
 /*
@@ -1542,7 +1548,7 @@ static int target_message(struct dm_ioctl *param, size_t param_size)
 
  if (r == 1) {
  param->flags |= DM_DATA_OUT_FLAG;
- if (buffer_test_overflow(result, maxlen))
+ if (dm_message_test_buffer_overflow(result, maxlen))
  param->flags |= DM_BUFFER_FULL_FLAG;
  else
  param->data_size = param->data_start + strlen(result) + 1;