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Ts'o" Cc: jack@suse.cz, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, riteshh@linux.ibm.com Subject: Re: [PATCH v7 11/11] ext4: introduce direct I/O write using iomap infrastructure Message-ID: <20191105205712.GB1739@bobrowski> References: <20191105162855.GK28764@mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191105162855.GK28764@mit.edu> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Nov 05, 2019 at 11:28:55AM -0500, Theodore Y. Ts'o wrote: > On Tue, Nov 05, 2019 at 11:02:39PM +1100, Matthew Bobrowski wrote: > > + ret = iomap_dio_rw(iocb, from, &ext4_iomap_ops, &ext4_dio_write_ops, > > + is_sync_kiocb(iocb) || unaligned_aio || extend); > > + > > + if (extend) > > + ret = ext4_handle_inode_extension(inode, offset, ret, count); > > + > > Can we do a slight optimization here like this? > > ret = iomap_dio_rw(iocb, from, &ext4_iomap_ops, &ext4_dio_write_ops, > is_sync_kiocb(iocb) || unaligned_aio || extend); > > if (extend && ret != -EBIOCQUEUED) > ret = ext4_handle_inode_extension(inode, offset, ret, count); > > > If iomap_dio_rw() returns -EBIOCQUEUED, there's no need to do any of > the ext4_handle_inode_extension --- in particular, there's no need to > call ext4_truncate_failed_write(), which has a bunch of extra > overhead, including taking and releasing i_data_sem. Hm, but for extension, unaligned asynchronous IO, or synchronous IO cases, 'wait_for_completion' within iomap_dio_rw() is set to true and as a result we'd never expect to receive -EIOCBQUEUED from iomap_dio_rw()? So, with that said, would the above change be necessary seeing as though we'd never expect ret == -EIOCBQUEUED when extend == true? Maybe I'm missing something? /M