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Wed, 13 Dec 2023 15:34:53 -0800 (PST) MIME-Version: 1.0 References: <20231213-zswap-dstmem-v1-0-896763369d04@bytedance.com> <20231213-zswap-dstmem-v1-2-896763369d04@bytedance.com> In-Reply-To: <20231213-zswap-dstmem-v1-2-896763369d04@bytedance.com> From: Yosry Ahmed Date: Wed, 13 Dec 2023 15:34:17 -0800 Message-ID: Subject: Re: [PATCH 2/5] mm/zswap: change dstmem size to one page To: Chengming Zhou Cc: Andrew Morton , Nhat Pham , Chris Li , Johannes Weiner , Seth Jennings , Dan Streetman , Vitaly Wool , linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 2C42B180014 X-Stat-Signature: szgcshjw6q8pmdyz1ka8xynarqy7nrbd X-Rspam-User: X-HE-Tag: 1702510494-429065 X-HE-Meta: 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 MogNauV/ rmcRwmIdRvnS+SrtAQH/HBY0KH+Qyxgx2EfQQLhCeOLCINp/uy+ZPUvUVvyBDwcuQb52AnC9cI5CMP/KPxySKEqOgdwhun/eWKDsbFK2DKHPCHj4PcWiSRXImO6ODIF4XJi1MmMn8a6DdfxOvdi10ST0K1RpooTg4nTog+adSP6F4V42spwARA7Zs14waaxQxXf4ZqRYaQm/dOqVlMyP9Cp9F7mkTnrrHHxsEZfci9ZUkZvFq5r5HbrBpgfyu0O1+0KQ7ijs+gJ19hsLYOwtCJw7s4e21P2BSHzwF X-Bogosity: Ham, tests=bogofilter, spamicity=0.000010, 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 Tue, Dec 12, 2023 at 8:18=E2=80=AFPM Chengming Zhou wrote: > > Change the dstmem size from 2 * PAGE_SIZE to only one page since > we only need at most one page when compress, and the "dlen" is also > PAGE_SIZE in acomp_request_set_params(). If the output size > PAGE_SIZE > we don't wanna store the output in zswap anyway. > > So change it to one page, and delete the stale comment. I couldn't find the history of why we needed 2 * PAGE_SIZE, it would be nice if someone has the context, perhaps one of the maintainers. One potential reason is that we used to store a zswap header containing the swap entry in the compressed page for writeback purposes, but we don't do that anymore. Maybe we wanted to be able to handle the case where an incompressible page would exceed PAGE_SIZE because of that?