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Sun, 09 Nov 2025 20:49:32 -0800 (PST) Received: from google.com ([2401:fa00:8f:203:f189:dea3:4254:ff1e]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7b0cc17ad4asm10139624b3a.37.2025.11.09.20.49.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 09 Nov 2025 20:49:31 -0800 (PST) Date: Mon, 10 Nov 2025 13:49:26 +0900 From: Sergey Senozhatsky To: Yuwen Chen Cc: axboe@kernel.dk, akpm@linux-foundation.org, bgeffon@google.com, licayy@outlook.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, liumartin@google.com, minchan@kernel.org, richardycc@google.com, senozhatsky@chromium.org Subject: Re: [PATCH v4] zram: Implement multi-page write-back Message-ID: References: <83d64478-d53c-441f-b5b4-55b5f1530a03@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 278E2C0006 X-Stat-Signature: kw5jy18hywmos3gw8q5g9bju8tiybt5p X-Rspam-User: X-HE-Tag: 1762750172-959491 X-HE-Meta: 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 O5QG6yyB xIx9uUpixU718EwP9kNCv2E7vmjH22guAnV6PRBX2dqleU7iZISQreX5Ow/QIOH6GiQ02nrF4xZh71lFPUBazm+dADiIWaaD9uX1M9qA+zo+KxL+rhtXBmHbkaS4iXImkEajGbS6pBLxXpxjOkSDV1Re8HGxl7RYAO2NluuA97A/M6MLnSCjO0w+D49cK3Wr78nA+cql0o4tLrRmpyVaLa4lQPMwX/VU/9iUaaUFgFXl5eoOBDVHmYdAqpT02h/Je5p+EHJZ7vZemInSMFdkxzuIsjiZgHOut6SI+9dNyEllI+lfecCjS+IQXYE/ng0I8ZgsYfIQSWoNxzYHIa/HE3tVpnE4QkDkL/OoFR6inZJW3wdc= 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: On (25/11/06 09:49), Yuwen Chen wrote: > For block devices, sequential write performance is significantly > better than random write. Currently, zram's write-back function > only supports single-page operations, which fails to leverage > the sequential write advantage and leads to suboptimal performance. As a side note: You almost never do sequential writes to the backing device. The thing is, e.g. when zram is used as swap, page faults happen randomly and free up (slot-free) random page-size chunks (so random bits in zram->bitmap become clear), which then get overwritten (zram simply picks the first available bit from zram->bitmap) during next writeback. There is nothing sequential about that, in systems with sufficiently large uptime and sufficiently frequent writeback/readback events writeback bitmap becomes sparse, which results in random IO, so your test tests an ideal case that almost never happens in practice.