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zram: document writeback_batch_size

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Add missing writeback_batch_size documentation.

Link: https://lkml.kernel.org/r/20251201094754.4149975-4-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Stevens <stevensd@google.com>
Cc: Minchan Kim <minchan@google.com>
Cc: Richard Chang <richardycc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Sergey Senozhatsky
2025-12-01 18:47:50 +09:00
committed by Andrew Morton
parent 4c1d61389e
commit 2502673aed
2 changed files with 17 additions and 1 deletions
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7
Documentation/ABI/testing/sysfs-block-zram
View File

@@ -157,3 +157,10 @@ Contact: Richard Chang <richardycc@google.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@chromium.org>
Description:
The writeback_batch_size device atrribute sets the maximum
number of in-flight writeback operations.

11
Documentation/admin-guide/blockdev/zram.rst
View File

@@ -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.