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Wong" To: Christoph Hellwig Cc: Jens Axboe , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, hannes@cmpxchg.org, clm@meta.com, linux-kernel@vger.kernel.org, willy@infradead.org, kirill@shutemov.name, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, bfoster@redhat.com Subject: Re: [PATCH 14/17] iomap: make buffered writes work with RWF_UNCACHED Message-ID: <20241212062641.GD6678@frogsfrogsfrogs> References: <20241114152743.2381672-2-axboe@kernel.dk> <20241114152743.2381672-16-axboe@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 03161120005 X-Stat-Signature: 1x9kk6pgmdznhdi11uop5ytcydzrf9wp X-HE-Tag: 1733984769-915179 X-HE-Meta: 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 Ga4tIPRC LN9GSl4siws2N7Q4fxYohIBtggINzuT3oqbqkhqi5FzCFaXexcUB+Lq3/YNbBAhuZYdEFNbzy/ZlBB9Hbo0/qB+EPWIGcOldju7GvTBjk+Ayuzhm2sUpfyS98UubkTDLKEOyXWsD36ATFEfFbSeMtxMYHHDhlwATw6Wr7wkkzJTo9gr5gitEfaOnAxYA4g6PwVrlGpvNJAif/SYHiMJ8W+b4QbslSfBs2KiQKZM91Zl0HSnF9yMkH8aSIUeUHLgh7zOcdsTkIn6SEWuiHpmWmdC/J1s/RzFVhu7TglqqXq3iShM8= 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, Dec 11, 2024 at 09:50:19PM -0800, Christoph Hellwig wrote: > On Thu, Nov 14, 2024 at 08:25:18AM -0700, Jens Axboe wrote: > > + if (iocb->ki_flags & IOCB_UNCACHED) > > + iter.flags |= IOMAP_UNCACHED; > > > > - while ((ret = iomap_iter(&iter, ops)) > 0) > > + while ((ret = iomap_iter(&iter, ops)) > 0) { > > + if (iocb->ki_flags & IOCB_UNCACHED) > > + iter.iomap.flags |= IOMAP_F_UNCACHED; > > iomap.flags and the IOMAP_F_* namespace is used to communicate flags > from the file system to the iomap core, so this looks wrong. Not entirely true -- IOMAP_F_SIZE_CHANGED is used to communicate state from iomap to gfs2, and IOMAP_F_STALE is set/checked only by the iomap core. iomap.h even says as much. Though given that there's a 4-byte gap in struct iomap between flags and the bdev pointer (at least on 64-bit) maybe we should make a separate field for these iomap state bits? > > size_t poff = offset_in_folio(folio, pos); > > int error; > > > > + if (folio_test_uncached(folio)) > > + wpc->iomap.flags |= IOMAP_F_UNCACHED; > > I guess this is what actually makes it work. Note that with the iomap > zoned series I posted yesteday things change a bit here in that the flags > in the wpc are decouple from the iomap flags, and this would now become > a wpc only flag as it isn't really a fs to iomap cummunication, but > based on iomap / page cache state. Hrmmm I'll go take a second look at that patch in the morning in case a better idea comes along. --D