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Tue, 12 Nov 2024 04:12:18 -0500 (EST) Date: Tue, 12 Nov 2024 11:12:15 +0200 From: "Kirill A. Shutemov" To: Jens Axboe Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, hannes@cmpxchg.org, clm@meta.com, linux-kernel@vger.kernel.org, willy@infradead.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH 03/16] mm: add PG_uncached page flag Message-ID: References: <20241111234842.2024180-1-axboe@kernel.dk> <20241111234842.2024180-4-axboe@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241111234842.2024180-4-axboe@kernel.dk> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 53A6F100005 X-Stat-Signature: 7a4wgtmogxfh4ohwt4fui5f9y455rcq9 X-Rspam-User: X-HE-Tag: 1731402698-13104 X-HE-Meta: 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 3RhiVv1S uLgb+CY285L97Cry7HRTpbnKcM0RLH/KfPKEUOUf6SSWVSxUZKEceFcsfUfRhzuz58L2Kd1DLXPHOU3eNAuFNZpwktccrJ0QJFdfbgHBiRl5+edCUqZe8mDjbAE6oqP+SC5yyn7w8fXI1YF5UTEx8aBll3qFccsTmz6/R5BD7thore89i/wl8ppPo7OlGEF1ejYu9M8QF7sleC8lXyNyxXsplSRDSLL9+SYdHX5BCi/4H1pYa9BROa6tEs2yTgPk9g6jjip9X/KBvUq6s+feDyeBuPZBsgUNL1+saVCmEA6a5blfmeSg489kWRs4Q63xJElMfzwUqqor6Rlx3cm7CVyTaBUwEuhyGmi3kLEM51Yjc3nO5OBNMK0kX9J2mZMNYyYHhhSLaYEH/a6OkZXWlrzp0tYbXXU56dlyxHbaAVjLSQsxFiusPHGWM/+cD1D+wC43Ir0pAKCCPdkZU2wx1Jjsz3/F/gvyjiFSj 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 Mon, Nov 11, 2024 at 04:37:30PM -0700, Jens Axboe wrote: > Add a page flag that file IO can use to indicate that the IO being done > is uncached, as in it should not persist in the page cache after the IO > has been completed. I have not found a way to avoid using a new bit. I am unsure if we have enough bits on 32-bit systems with all possible features enabled. In the worst-case scenario, we may need to make the feature 64-bit only. I believe it should be acceptable as long as userspace is prepared for the possibility that RWF_UNCACHED may fail. It is not going to be supported by all filesystems anyway. -- Kiryl Shutsemau / Kirill A. Shutemov