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Wong" Cc: Brian Foster , linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 3/7] iomap: optional zero range dirty folio processing Message-ID: References: <20250605173357.579720-1-bfoster@redhat.com> <20250605173357.579720-4-bfoster@redhat.com> <20250609160420.GC6156@frogsfrogsfrogs> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250609160420.GC6156@frogsfrogsfrogs> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Rspamd-Queue-Id: 4C20580004 X-Stat-Signature: ufb6suux4djrari8ni73yagu5gya97gq X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1749529629-876806 X-HE-Meta: U2FsdGVkX182nm3LGXiMLovc91htP4RVOB/OT0s74AB0LhkuMIrgWJg2IcORqogF2N4O11/BK9e9X4+KGbH1AXFUBXISTCW6ahQEWptQIFE8PGYUi9R7RpASC4WB5voagNkokqxis1M8UYKUtFqawtqrxDvj/38pa+O5dpmcad4Tg9SkmZs/TnzEJDHZ43XKpEDuBcP8zO+58+jXgbAjZUBu5ezYXJhA3EjJFs/86ewUIFHExqn7mS6GbHlNcG3ylLd6SucMh7TJrZFSqSdJXd+878kzppg0jj5AT6uEPxMYy2GGCDoJ+nGpMCEZF4omSMw23jzduWj2X71iRT39SNJxlDBqYLIrhm38F9BzCYhwgU9DDoaSGlCTXS4a5biSPBXSaAOqsO0mZbT28TT87+ayNx33y6DsJxMa5crWySzCIA/+mdubYLUnFDkn1b1PExNo5BvYKRV7WYEvhFc/6WilODKTDvom6l5MApcNvQJ9bLocDhTwWtoeRUR1JdZaBn/Z+NLvAu/WYIB1PgVdBQqTKLMd/BjuY6aM9WiDi6J+BW7lZjrr6MT00cOGpkjzTbYZwCy/txwc/20wUS6DI2raO7JXq4yi6eZboGG/1M0uong11JwUvtxwmA8Jc5R+3UYuGz7vqv1f66PQZ+HPf+X8oJG7ElkS23McfyNJWixb13xDkfERendbm4bVeLRChOFIZB8kXJQqBMaJgrcPJE6ZBPhC6Jt3mX9kwoBnAS9ETEWj0fA7vEl5J9SE8+zTs9G6BqLu57aH3HmzBX46zZzJT6wVoQdElT9AKDeJ1MjTxEOP4bMFdOj6iua3qwnhHbetF3znAK+UbYY3LcfsSxVIVMQjz6ONL8EDOR/HsYbo0X3wzvzN0Zs2F2lqenI7z0YeIwdY641i2Fx9C7pYG2id3xSkUnn5N1EciH/whoC1vU47zh+moPdsnUzQqLpqBJxmloE/z/pnK+2v9sE v7ABNE55 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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 Mon, Jun 09, 2025 at 09:04:20AM -0700, Darrick J. Wong wrote: > > + if (iter->fbatch) { > > + struct folio *folio = folio_batch_next(iter->fbatch); > > + > > + if (folio) { > > + folio_get(folio); > > + folio_lock(folio); > > Hrm. So each folio that is added to the batch isn't locked, nor does > the batch (or iomap) hold a refcount on the folio until we get here. find_get_entry references a folio, and filemap_get_folios_dirty preserves that reference. It will be released in folio_batch_release. So this just add an extra reference for local operation so that the rest of iomap doesn't need to know about that magic. > Do > we have to re-check that folio->{mapping,index} match what iomap is > trying to process? Or can we assume that nobody has removed the folio > from the mapping? That's a good point, though as without having the folio locked it could get truncated, so I think we'll have to redo the truncate check here.