zram: deprecate zram attrs sysfs nodes

Add Documentation/ABI/obsolete/sysfs-block-zram file and list obsolete and
deprecated attributes there.  The patch also adds additional information
to zram documentation and describes the basic strategy:

- the existing RW nodes will be downgraded to WO nodes (in 4.11)
- deprecated RO sysfs nodes will eventually be removed (in 4.11)

Users will be additionally notified about deprecated attr usage by
pr_warn_once() (added to every deprecated attr _show()), as suggested by
Minchan Kim.

User space is advised to use zram<id>/stat, zram<id>/io_stat and
zram<id>/mm_stat files.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-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, 135 insertions, 0 deletions

diff --git a/Documentation/ABI/obsolete/sysfs-block-zram b/Documentation/ABI/obsolete/sysfs-block-zram
new file mode 100644
index 000000000000..720ea92cfb2e
--- /dev/null
+++ b/Documentation/ABI/obsolete/sysfs-block-zram
@@ -0,0 +1,119 @@
+What:		/sys/block/zram<id>/num_reads
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The num_reads file is read-only and specifies the number of
+		reads (failed or successful) done on this device.
+		Now accessible via zram<id>/stat node.
+
+What:		/sys/block/zram<id>/num_writes
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The num_writes file is read-only and specifies the number of
+		writes (failed or successful) done on this device.
+		Now accessible via zram<id>/stat node.
+
+What:		/sys/block/zram<id>/invalid_io
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The invalid_io file is read-only and specifies the number of
+		non-page-size-aligned I/O requests issued to this device.
+		Now accessible via zram<id>/io_stat node.
+
+What:		/sys/block/zram<id>/failed_reads
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The failed_reads file is read-only and specifies the number of
+		failed reads happened on this device.
+		Now accessible via zram<id>/io_stat node.
+
+What:		/sys/block/zram<id>/failed_writes
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The failed_writes file is read-only and specifies the number of
+		failed writes happened on this device.
+		Now accessible via zram<id>/io_stat node.
+
+What:		/sys/block/zram<id>/notify_free
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The notify_free file is read-only. Depending on device usage
+		scenario it may account a) the number of pages freed because
+		of swap slot free notifications or b) the number of pages freed
+		because of REQ_DISCARD requests sent by bio. The former ones
+		are sent to a swap block device when a swap slot is freed, which
+		implies that this disk is being used as a swap disk. The latter
+		ones are sent by filesystem mounted with discard option,
+		whenever some data blocks are getting discarded.
+		Now accessible via zram<id>/io_stat node.
+
+What:		/sys/block/zram<id>/zero_pages
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The zero_pages file is read-only and specifies number of zero
+		filled pages written to this disk. No memory is allocated for
+		such pages.
+		Now accessible via zram<id>/mm_stat node.
+
+What:		/sys/block/zram<id>/orig_data_size
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The orig_data_size file is read-only and specifies uncompressed
+		size of data stored in this disk. This excludes zero-filled
+		pages (zero_pages) since no memory is allocated for them.
+		Unit: bytes
+		Now accessible via zram<id>/mm_stat node.
+
+What:		/sys/block/zram<id>/compr_data_size
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The compr_data_size file is read-only and specifies compressed
+		size of data stored in this disk. So, compression ratio can be
+		calculated using orig_data_size and this statistic.
+		Unit: bytes
+		Now accessible via zram<id>/mm_stat node.
+
+What:		/sys/block/zram<id>/mem_used_total
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The mem_used_total file is read-only and specifies the amount
+		of memory, including allocator fragmentation and metadata
+		overhead, allocated for this disk. So, allocator space
+		efficiency can be calculated using compr_data_size and this
+		statistic.
+		Unit: bytes
+		Now accessible via zram<id>/mm_stat node.
+
+What:		/sys/block/zram<id>/mem_used_max
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The mem_used_max file is read/write and specifies the amount
+		of maximum memory zram have consumed to store compressed data.
+		For resetting the value, you should write "0". Otherwise,
+		you could see -EINVAL.
+		Unit: bytes
+		Downgraded to write-only node: so it's possible to set new
+		value only; its current value is stored in zram<id>/mm_stat
+		node.
+
+What:		/sys/block/zram<id>/mem_limit
+Date:		August 2015
+Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+Description:
+		The mem_limit file is read/write and specifies the maximum
+		amount of memory ZRAM can use to store the compressed data.
+		The limit could be changed in run time and "0" means disable
+		the limit.  No limit is the initial state.  Unit: bytes
+		Downgraded to write-only node: so it's possible to set new
+		value only; its current value is stored in zram<id>/mm_stat
+		node.
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 7920f4026d36..48a183e29988 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -128,6 +128,22 @@ mem_limit         RW    the maximum amount of memory ZRAM can use to store
 num_migrated      RO    the number of objects migrated migrated by compaction
 
 
+WARNING
+=======
+per-stat sysfs attributes are considered to be deprecated.
+The basic strategy is:
+-- the existing RW nodes will be downgraded to WO nodes (in linux 4.11)
+-- deprecated RO sysfs nodes will eventually be removed (in linux 4.11)
+
+The list of deprecated attributes can be found here:
+Documentation/ABI/obsolete/sysfs-block-zram
+
+Basically, every attribute that has its own read accessible sysfs node
+(e.g. num_reads) *AND* is accessible via one of the stat files (zram<id>/stat
+or zram<id>/io_stat or zram<id>/mm_stat) is considered to be deprecated.
+
+User space is advised to use the following files to read the device statistics.
+
 File /sys/block/zram<id>/stat
 
 Represents block layer statistics. Read Documentation/block/stat.txt for