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zram: add config and doc file for writeback feature

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

Link: http://lkml.kernel.org/r/1498459987-24562-10-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Juneho Choi <juno.choi@lge.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Minchan Kim 2017-09-06 16:20:10 -07:00 committed by Linus Torvalds
parent 8e654f8fbf
commit 5a47074f02
3 changed files with 31 additions and 0 deletions
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8
Documentation/ABI/testing/sysfs-block-zram
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@ -90,3 +90,11 @@ Description:
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.

11
Documentation/blockdev/zram.txt
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@ -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 @@ line of text and contains the following stats separated by whitespace:
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

12
drivers/block/zram/Kconfig
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@ -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.