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Wong" , 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: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Rspamd-Queue-Id: E21D1A0005 X-Stat-Signature: agqyj7s1rif8gu6fcmar66squ8a4u14s X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1749557867-834385 X-HE-Meta: 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 QH9xoOKX fHKCkf1TRoQTvejsEnZQX/h76YdVKnrZ0mgRo2ml12m0zqrk+r65eK3HdHn+ui3+VJtcjSd56uJ5Lqu4KXcPk9gmSAtYjL2yPRPWHC9RLQzQuupIzL1OKvjD7mDrIb1rOYQxu33YymwF/eoAt4mOwko82MV5xKVWy9yipRJSAhy95xAzuaXSNQ1yKSRkhsIRBQhJaebBd0RXOToDWu8jZdf4QNtf3jkBHu4XkJeywJkuUkPnOUX++Yh6bQRqdBCmkKA1uvVV5JzNrPCk+xfmZwF4pnrIuf9vHnEdoNDcrAXmEcA76wOFJ+p71CDLVy+8+LWsr0B3FLsV9lDeLOSd4hhakoDMiT8hO1gfynnz5EbZ12fk= 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 09:27:07PM -0700, Christoph Hellwig wrote: > 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. > Exactly. > > 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. > > Hm Ok thanks, I'll take a closer look at that.. Brian