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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rQ7HM-00000000Cg9-1PbJ; Wed, 17 Jan 2024 14:52:32 +0000 Date: Wed, 17 Jan 2024 14:52:32 +0000 From: Matthew Wilcox To: Jan Kara Cc: Christian Brauner , lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-btrfs@vger.kernel.org, linux-block@vger.kernel.org, Christoph Hellwig Subject: Re: [LSF/MM/BPF TOPIC] Dropping page cache of individual fs Message-ID: References: <20240116-tagelang-zugnummer-349edd1b5792@brauner> <20240116114519.jcktectmk2thgagw@quack3> <20240117-tupfen-unqualifiziert-173af9bc68c8@brauner> <20240117143528.idmyeadhf4yzs5ck@quack3> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240117143528.idmyeadhf4yzs5ck@quack3> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 6BEDD14001E X-Stat-Signature: ouauyimxetmke7gkc7onez7y7rj3hefi X-Rspam-User: X-HE-Tag: 1705503157-422807 X-HE-Meta: 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 Kr165gWD CVBCMhTbc8cCg45FN9EdgT522OYrRUzIe2cZEIMFEJsQT9552W+bwGUkXddbOxFX/kCbZtxs69Nahw7nOBQI7O4zS5z9taG9PANczvkAQ+0eDfFNUwMeZOvAE31qVpTlUzAWbTKQP8OTNsLeuLJkmC53omdF3BV/G6CwZ5Re4oGbFZM+1SJ1ESn0FUr4+zQcMRx8+6iTlGBXDIU/yfcfK1Gthkw== 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 Wed, Jan 17, 2024 at 03:35:28PM +0100, Jan Kara wrote: > OK. So could we then define the effect of your desired call as calling > posix_fadvise(..., POSIX_FADV_DONTNEED) for every file? This is kind of > best-effort eviction which is reasonably well understood by everybody. I feel like we're in an XY trap [1]. What Christian actually wants is to not be able to access the contents of a file while the device it's on is suspended, and we've gone from there to "must drop the page cache". We have numerous ways to intercept file reads and make them either block or fail. The obvious one to me is security_file_permission() called from rw_verify_area(). Can we do everything we need with an LSM? [1] https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem