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Wong" , linux-xfs@vger.kernel.org, linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner Subject: Re: [PATCH 1/3] xfs: Remove xfs_filemap_map_pages() wrapper Message-ID: References: <20230208145335.307287-1-willy@infradead.org> <20230208145335.307287-2-willy@infradead.org> <20230208215311.GC360264@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230208215311.GC360264@dread.disaster.area> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 85B1F20012 X-Stat-Signature: k1y33z8fuk5n1musc9uxqy345y16iwc1 X-HE-Tag: 1675910669-659458 X-HE-Meta: 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 ehdoXHRw lD2oPp3gBRaDV4HSpUW3iaf73rfqWgLBxeGySdbtpNtIf90wxGfryDPCdKUFcAhGKKYduQ72G0JjstUlnZACUwYq6FaXXVAlwsM+FWAJpVwI2+wTpLKuS+oVOuQFnCglsmgMIFixtWGG3xxzPMu4SLhN1+7yjrw7fUH7MTxJX5D8A/QcoEsbmhfHvKlpWvzI/dOhc7/g5lK1YMHE= 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: On Thu, Feb 09, 2023 at 08:53:11AM +1100, Dave Chinner wrote: > > If XFS really needs it, > > it can trylock the semaphore and return 0 if it fails, falling back to > > the ->fault path. But I don't think XFS actually needs it. > > > > The ->map_pages path trylocks the folio, checks the folio->mapping, > > checks uptodate, then checks beyond EOF (not relevant to hole punch). > > Then it takes the page table lock and puts the page(s) into the page > > tables, unlocks the folio and moves on to the next folio. > > > > The hole-punch path, like the truncate path, takes the folio lock, > > unmaps the folio (which will take the page table lock) and removes > > it from the page cache. > > > > So what's the race? > > Hole punch is a multi-folio operation, so while we are operating on > invalidating one folio, another folio in the range we've already > invalidated could be instantiated and mapped, leaving mapped > up-to-date pages over a range we *require* the page cache to empty. Nope. ->map_pages is defined to _not_ instantiate new pages. If there are uptodate pages in the page cache, they can be mapped, but missing pages will be skipped, and left to ->fault to bring in.