docs: device-mapper: move it to the admin-guide

The DM support describes lots of aspects related to mapped
disk partitions from the userspace PoV.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

1 files changed, 0 insertions, 225 deletions

diff --git a/Documentation/device-mapper/statistics.rst b/Documentation/device-mapper/statistics.rst
deleted file mode 100644
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-=============
-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.  When the histogram
-argument is used, the 14th parameter is reported that represents the
-histogram of latencies.  All these counters may be accessed by sending
-the @stats_print message to the appropriate DM device via dmsetup.
-
-The reported times are in milliseconds and the granularity depends on
-the kernel ticks.  When the option precise_timestamps is used, the
-reported times are in nanoseconds.
-
-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> [<number_of_optional_arguments> <optional_arguments>...] [<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.
-
-	<number_of_optional_arguments>
-	  The number of optional arguments
-
-	<optional_arguments>
-	  The following optional arguments are supported:
-
-	  precise_timestamps
-		use precise timer with nanosecond resolution
-		instead of the "jiffies" variable.  When this argument is
-		used, the resulting times are in nanoseconds instead of
-		milliseconds.  Precise timestamps are a little bit slower
-		to obtain than jiffies-based timestamps.
-	  histogram:n1,n2,n3,n4,...
-		collect histogram of latencies.  The
-		numbers n1, n2, etc are times that represent the boundaries
-		of the histogram.  If precise_timestamps is not used, the
-		times are in milliseconds, otherwise they are in
-		nanoseconds.  For each range, the kernel will report the
-		number of requests that completed within this range. For
-		example, if we use "histogram:10,20,30", the kernel will
-		report four numbers a:b:c:d. a is the number of requests
-		that took 0-10 ms to complete, b is the number of requests
-		that took 10-20 ms to complete, c is the number of requests
-		that took 20-30 ms to complete and d is the number of
-		requests that took more than 30 ms to complete.
-
-	<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.
-	  If we omit the number of optional arguments, program id must not
-	  be a number, otherwise it would be interpreted as the number of
-	  optional arguments.
-
-	<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>
-	        precise_timestamps histogram:n1,n2,n3,...
-
-	The strings "precise_timestamps" and "histogram" are printed only
-	if they were specified when creating the region.
-
-    @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 auxiliary 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