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Commit bc6f4ed9 authored by Minchan Kim's avatar Minchan Kim Committed by Peter Kalauskas
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UPSTREAM: zram: add config and doc file for writeback feature 

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: default avatarMinchan Kim <minchan@kernel.org>
Cc: Juneho Choi <juno.choi@lge.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>

(cherry picked from commit 5a47074f0279421778f97b1b1e75686696a5f42a)
Signed-off-by: default avatarPeter Kalauskas <peskal@google.com>
Bug: 112488418
Change-Id: I6bac58eeab7125f49eefb77823981aae67f78a68
parent 0a6c1999

Documentation/ABI/testing/sysfs-block-zram

+8 −0
Original line number Diff line number Diff line
@@ -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.

Documentation/blockdev/zram.txt

+11 −0
Original line number Diff line number Diff line
@@ -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

drivers/block/zram/Kconfig

+12 −0
Original line number Diff line number Diff line
@@ -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.