From: Sergey Senozhatsky Date: Mon, 1 Dec 2025 09:47:50 +0000 (+0900) Subject: zram: document writeback_batch_size X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2502673aed6c66befc7efc2dc008e2a8a50508cd;p=thirdparty%2Fkernel%2Flinux.git zram: document writeback_batch_size Add missing writeback_batch_size documentation. Link: https://lkml.kernel.org/r/20251201094754.4149975-4-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky Cc: Brian Geffon Cc: David Stevens Cc: Minchan Kim Cc: Richard Chang Signed-off-by: Andrew Morton --- diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram index ed10c2e4b5c29..e538d4850d611 100644 --- a/Documentation/ABI/testing/sysfs-block-zram +++ b/Documentation/ABI/testing/sysfs-block-zram @@ -157,3 +157,10 @@ Contact: Richard Chang Description: The writeback_compressed device atrribute toggles compressed writeback feature. + +What: /sys/block/zram/writeback_batch_size +Date: November 2025 +Contact: Sergey Senozhatsky +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 9547e4e959791..94bb7f2245eef 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/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.