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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rfBSi-00000004EmB-20fq; Wed, 28 Feb 2024 04:22:32 +0000 Date: Wed, 28 Feb 2024 04:22:32 +0000 From: Matthew Wilcox To: Kent Overstreet Cc: Linus Torvalds , Dave Chinner , Luis Chamberlain , lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm , Daniel Gomez , Pankaj Raghav , Jens Axboe , Christoph Hellwig , Chris Mason , Johannes Weiner Subject: Re: [LSF/MM/BPF TOPIC] Measuring limits and enhancing buffered IO Message-ID: References: <4rde5abojkj6neokif4j6z4bgkqwztowfiiklpvxramiuhvzjb@ts5af6w4bl4t> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: fy31dyi1q5hmmmzs3kujej7t3e1m1zyi X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B691710000D X-HE-Tag: 1709094161-9369 X-HE-Meta: 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 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, Feb 28, 2024 at 03:00:36AM +0000, Matthew Wilcox wrote: > On Tue, Feb 27, 2024 at 09:22:26PM -0500, Kent Overstreet wrote: > > Which does raise the question of if we've ever attempted to define a > > lock ordering on folios. I suspect not, since folio lock doesn't even > > seem to have lockdep support. > > We even wrote it down! > > /* > * To avoid deadlocks between range_cyclic writeback and callers > * that hold pages in PageWriteback to aggregate I/O until > * the writeback iteration finishes, we do not loop back to the > * start of the file. Doing so causes a page lock/page > * writeback access order inversion - we should only ever lock > * multiple pages in ascending page->index order, and looping > * back to the start of the file violates that rule and causes > * deadlocks. > */ > > (I'll take the AR to put this somewhere better like in the folio_lock() > kernel-doc) Um. I already did. * Context: May sleep. If you need to acquire the locks of two or * more folios, they must be in order of ascending index, if they are * in the same address_space. If they are in different address_spaces, * acquire the lock of the folio which belongs to the address_space which * has the lowest address in memory first. Where should I have put this information that you would have found it, if not in the kernel-doc for folio_lock()?