linux-kernel - [PATCHv2 3/7] zram: document writeback_batch

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Message-ID: <20251201094754.4149975-4-senozhatsky@chromium.org>
Date: Mon,  1 Dec 2025 18:47:50 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Richard Chang <richardycc@...gle.com>,
	Minchan Kim <minchan@...nel.org>
Cc: Brian Geffon <bgeffon@...gle.com>,
	David Stevens <stevensd@...gle.com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-block@...r.kernel.org,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCHv2 3/7] zram: document writeback_batch_size

Add missing writeback_batch_size documentation.

Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 Documentation/ABI/testing/sysfs-block-zram  |  7 +++++++
 Documentation/admin-guide/blockdev/zram.rst | 11 ++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index ed10c2e4b5c2..e538d4850d61 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -157,3 +157,10 @@ Contact:	Richard Chang <richardycc@...gle.com>
 Description:
 		The writeback_compressed device atrribute toggles compressed
 		writeback feature.
+
+What:		/sys/block/zram<id>/writeback_batch_size
+Date:		November 2025
+Contact:	Sergey Senozhatsky <senozhatsky@...omium.org>
+Description:
+		The writeback_batch_size device atrribute sets the maximum
+		number of in-flight writeback operations.
diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index 9547e4e95979..94bb7f2245ee 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -214,6 +214,8 @@ mem_limit         	WO	specifies the maximum amount of memory ZRAM can
 writeback_limit   	WO	specifies the maximum amount of write IO zram
 				can write out to backing device as 4KB unit
 writeback_limit_enable  RW	show and set writeback_limit feature
+writeback_batch_size	RW	show and set maximum number of in-flight
+				writeback operations
 writeback_compressed	RW	show and set compressed writeback feature
 comp_algorithm    	RW	show and change the compression algorithm
 algorithm_params	WO	setup compression algorithm parameters
@@ -223,7 +225,6 @@ backing_dev	  	RW	set up backend storage for zram to write out
 idle		  	WO	mark allocated slot as idle
 ======================  ======  ===============================================
 
-
 User space is advised to use the following files to read the device statistics.
 
 File /sys/block/zram<id>/stat
@@ -447,6 +448,14 @@ this feature, execute::
 Note that this feature should be configured before the `zramX` device is
 initialized.
 
+Depending on backing device storage type, writeback operation may benefit
+from a higher number of in-flight write requests (batched writes).  The
+number of maximum in-flight writeback operations can be configured via
+`writeback_batch_size` attribute.  To change the default value (which is 32),
+execute::
+
+	$ echo 64 > /sys/block/zramX/writeback_batch_size
+
 If admin wants to measure writeback count in a certain period, they could
 know it via /sys/block/zram0/bd_stat's 3rd column.
 
-- 
2.52.0.487.g5c8c507ade-goog