Documentation: dm-integrity: Document the meaning of "buffer".

"Buffers" are buffers of the metadata/checksum area of dm-integrity.
They are always at most as large as a single metadata area on-disk, but
may be smaller.
Signed-off-by: Russell Harmon <eatnumber1@gmail.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Documentation/admin-guide/device-mapper/dm-integrity.rst

@@ -38,6 +38,15 @@ the device. But it will only format the device if the superblock contains
 zeroes. If the superblock is neither valid nor zeroed, the dm-integrity
 target can't be loaded.
 
+Accesses to the on-disk metadata area containing checksums (aka tags) are
+buffered using dm-bufio. When an access to any given metadata area
+occurs, each unique metadata area gets its own buffer(s). The buffer size
+is capped at the size of the metadata area, but may be smaller, thereby
+requiring multiple buffers to represent the full metadata area. A smaller
+buffer size will produce a smaller resulting read/write operation to the
+metadata area for small reads/writes. The metadata is still read even in
+a full write to the data covered by a single buffer.
+
 To use the target for the first time:
 
 1. overwrite the superblock with zeroes
@@ -106,10 +115,6 @@ buffer_sectors:number
 	The number of sectors in one buffer. The value is rounded down to
 	a power of two.
 
-	The tag area is accessed using buffers, the buffer size is
-	configurable. The large buffer size means that the I/O size will
-	be larger, but there could be less I/Os issued.
-
 journal_watermark:number
 	The journal watermark in percents. When the size of the journal
 	exceeds this watermark, the thread that flushes the journal will