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Tue, 19 Mar 2024 09:41:10 -0700 (PDT) MIME-Version: 1.0 References: <1668172.1709764777@warthog.procyon.org.uk> <1831809.1709807788@warthog.procyon.org.uk> <651179.1710857687@warthog.procyon.org.uk> In-Reply-To: From: Miklos Szeredi Date: Tue, 19 Mar 2024 17:40:58 +0100 Message-ID: Subject: Re: [RFC PATCH] mm: Replace ->launder_folio() with flush and wait To: David Howells Cc: Matthew Wilcox , Trond Myklebust , Christoph Hellwig , Andrew Morton , Alexander Viro , Christian Brauner , Jeff Layton , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, netfs@lists.linux.dev, v9fs@lists.linux.dev, linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org, linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: DA3EB20014 X-Rspam-User: X-Stat-Signature: 3ubrroas3ht5k1wf5aaogbjm55rfsf7s X-Rspamd-Server: rspam01 X-HE-Tag: 1710866471-884393 X-HE-Meta: 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 BYVTgruB V2a/Xrtgc/QhqP2xX1oY7sKFsYAcm8EXQ/rVO2x/GtZXqDYA9He3uyxQXpaNBMDfWBJUzld3bU+OyNidFw5GO7A7AymI+6YJceNWgNd5Hk4zTRYEOMS9TQcs0gbZZfyQnFxJsoSfSRMp0t7QUHxnmy20dbcpfnzmNCJDCDUosl4sQBhBCc3SoDgdIYUrbhFvFQwL5Rg87+w15FLYkEljoO61bD/So+97ZS5s8UAIW2bMWqKy0BDB18s4Vo11uaRmXSGxG1mrXKDYxwwV54cUaqqzFE9s9tOPNX2VjeFX2HJopF3M= X-Bogosity: Ham, tests=bogofilter, spamicity=0.001300, 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, 19 Mar 2024 at 17:13, Miklos Szeredi wrote: > > On Tue, 19 Mar 2024 at 15:15, David Howells wrote: > > > What particular usage case of invalidate_inode_pages2() are you thinking of? > > FUSE_NOTIFY_INVAL_INODE will trigger invalidate_inode_pages2_range() > to clean up the cache. > > The server is free to discard writes resulting from this invalidation > and delay reads in the region until the invalidation finishes. This > would no longer work with your change, since the mapping could > silently be reinstated between the writeback and the removal from the > cache due to the page being unlocked/relocked. This would also matter if a distributed filesystem wanted to implement coherence even if there are mmaps. I.e. a client could get exclusive access to a region by issuing FUSE_NOTIFY_INVAL_INODE on all other clients and blocking reads. With your change this would fail. Again, this is purely theoretical, and without a way to differentiate between the read-only and write cases it has limited usefulness. Adding leases to fuse (which I plan to do) would make this much more useful. Thanks, Miklos