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Mon, 01 Dec 2025 01:48:14 -0800 (PST) Received: from tigerii.tok.corp.google.com ([2a00:79e0:2031:6:943c:f651:f00f:2459]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7d15e7db577sm12882074b3a.31.2025.12.01.01.48.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Dec 2025 01:48:13 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton , Richard Chang , Minchan Kim Cc: Brian Geffon , David Stevens , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, Sergey Senozhatsky Subject: [PATCHv2 3/7] zram: document writeback_batch_size Date: Mon, 1 Dec 2025 18:47:50 +0900 Message-ID: <20251201094754.4149975-4-senozhatsky@chromium.org> X-Mailer: git-send-email 2.52.0.487.g5c8c507ade-goog In-Reply-To: <20251201094754.4149975-1-senozhatsky@chromium.org> References: <20251201094754.4149975-1-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 46CBA1C0007 X-Stat-Signature: qsqksxk5k57cau6ju8a853n41ut8hcws X-HE-Tag: 1764582495-703995 X-HE-Meta: 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 kR63H8jl GnjD0k507hi6NbfxHTPgwdFF3FgPL/gTQaSo3pPo3xu3h8WaUspPRf4bFPsk1aT+6jXDpqA7Xr1c3JUpASiL1zk9dMJI5UXibbbpdippJ9/sKe35H+ilu0dU0GRnEmwP2t9CbWKfU1RBDkvmp6uKzRoSVogcdyk3nGlyLCxTwwGpbh58B4ISeXP6sKxW5d1LnfldMGMLjOafChcVjw4bPT3tq3dhackWymX5wFJ+e20arA/qh4P2t4L6dNzT9E6IkP6u7aIidO3E64VVRdyrUMz/2jOcX8E4oRgUcpgdSgwTFtyBLsQv4TbaNy6uGat1r6fiimVUkSX4nrxSoWhoA0MSgq3tWElHJozhR/wQqJnhfK3Ajx6DqGHUBuw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Add missing writeback_batch_size documentation. Signed-off-by: Sergey Senozhatsky --- 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 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 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/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