zram: export new 'io_stat' sysfs attrs

Per-device `zram<id>/io_stat' file provides accumulated I/O statistics of
particular zram device in a format similar to block layer statistics.  The
file consists of a single line and represents the following stats
(separated by whitespace):

        failed_reads
        failed_writes
        invalid_io
        notify_free

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 20 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index 91ad7071b9e8..a7f622f9bcf6 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -149,3 +149,12 @@ Description:
                 The compact file is write-only and trigger compaction for
                 allocator zrm uses. The allocator moves some objects so that
                 it could free fragment space.
+
+What:           /sys/block/zram<id>/io_stat
+Date:           August 2015
+Contact:        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+                The io_stat file is read-only and accumulates device's I/O
+                statistics not accounted by block layer. For example,
+                failed_reads, failed_writes, etc. File format is similar to
+                block layer statistics file format.
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 971765ed5ac1..9610be3e9d36 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -133,6 +133,17 @@ File /sys/block/zram<id>/stat
 Represents block layer statistics. Read Documentation/block/stat.txt for
 details.
 
+File /sys/block/zram<id>/io_stat
+
+The stat file represents device's I/O statistics not accounted by block
+layer and, thus, not available in zram<id>/stat file. It consists of a
+single line of text and contains the following stats separated by
+whitespace:
+        failed_reads
+        failed_writes
+        invalid_io
+        notify_free
+
 8) Deactivate:
         swapoff /dev/zram0
         umount /dev/zram1