[PATCH v1 9/9] zram: add config and doc file for writeback feature

Minchan Kim
2017-06-26T06:53:56Z

This patch adds document and kconfig for using of writeback feature.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
Documentation/ABI/testing/sysfs-block-zram | 8 ++++++++
Documentation/blockdev/zram.txt | 11 +++++++++++
drivers/block/zram/Kconfig | 12 ++++++++++++
3 files changed, 31 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index 451b6d8..c1513c7 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -90,3 +90,11 @@ Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
device's debugging info useful for kernel developers. Its
format is not documented intentionally and may change
anytime without any notice.
+
+What: /sys/block/zram<id>/backing_dev
+Date: June 2017
+Contact: Minchan Kim <minchan@kernel.org>
+Description:
+ The backing_dev file is read-write and set up backing
+ device for zram to write incompressible pages.
+ For using, user should enable CONFIG_ZRAM_WRITEBACK.
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 4fced8a..257e657 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -168,6 +168,7 @@ max_comp_streams RW the number of possible concurrent compress operations
comp_algorithm RW show and change the compression algorithm
compact WO trigger memory compaction
debug_stat RO this file is used for zram debugging purposes
+backing_dev RW set up backend storage for zram to write out

User space is advised to use the following files to read the device statistics.
@@ -231,5 +232,15 @@ The stat file represents device's mm statistics. It consists of a single
resets the disksize to zero. You must set the disksize again
before reusing the device.

+* Optional Feature
+
+= writeback
+
+With incompressible pages, there is no memory saving with zram.
+Instead, with CONFIG_ZRAM_WRITEBACK, zram can write incompressible page
+to backing storage rather than keeping it in memory.
+User should set up backing device via /sys/block/zramX/backing_dev
+before disksize setting.
+
Nitin Gupta
ngupta@vflare.org
diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index b8ecba6..7cd4a8e 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -13,3 +13,15 @@ config ZRAM
disks and maybe many more.

See zram.txt for more information.
+
+config ZRAM_WRITEBACK
+ bool "Write back incompressible page to backing device"
+ depends on ZRAM
+ default n
+ help
+ With incompressible page, there is no memory saving to keep it
+ in memory. Instead, write it out to backing device.
+ For this feature, admin should set up backing device via
+ /sys/block/zramX/backing_dev.
+
+ See zram.txt for more infomration.
--
2.7.4