From: Jeff Moyer Subject: Re: [PATCH 2/9] ext4: honor the O_SYNC flag for aysnchronous direct I/O requests Date: Tue, 20 Nov 2012 15:02:15 -0500 Message-ID: References: <20121120074116.24645.36369.stgit@blackbox.djwong.org> <20121120074131.24645.38489.stgit@blackbox.djwong.org> <20121120100751.GB1408@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Darrick J. Wong" , axboe@kernel.dk, tytso@mit.edu, david@fromorbit.com, bpm@sgi.com, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, hch@infradead.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, xfs@oss.sgi.com To: Jan Kara Return-path: In-Reply-To: <20121120100751.GB1408@quack.suse.cz> (Jan Kara's message of "Tue, 20 Nov 2012 11:07:51 +0100") Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Jan Kara writes: >> @@ -1279,6 +1280,9 @@ struct ext4_sb_info { >> /* workqueue for dio unwritten */ >> struct workqueue_struct *dio_unwritten_wq; >> >> + /* workqueue for aio+dio+o_sync disk cache flushing */ >> + struct workqueue_struct *aio_dio_flush_wq; >> + > Umm, I'm not completely decided whether we really need a separate > workqueue. But it doesn't cost too much so I guess it makes some sense - > fsync() is rather heavy so syncing won't starve extent conversion... I'm assuming you'd like me to convert the names from flush to fsync, yes? >> + >> + /* >> + * If we are running in nojournal mode, just flush the disk >> + * cache and return. >> + */ >> + if (!journal) >> + return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_NOIO, NULL); > And this is wrong as well - you need to do work similar to what > ext4_sync_file() does. Actually it would be *much* better if these two > sites used the same helper function. Which also poses an interesting > question about locking - do we need i_mutex or not? Forcing a transaction > commit is definitely OK without it, similarly as grabbing transaction ids > from inode or ext4_should_journal_data() test. __sync_inode() call seems > to be OK without i_mutex as well so I believe we can just get rid of it > (getting i_mutex from the workqueue is a locking nightmare we don't want to > return to). Just to be clear, are you saying you would like me to remove the mutex_lock/unlock pair from ext4_sync_file? (I had already factored out the common code between this new code path and the fsync path in my tree.) >> @@ -149,8 +209,11 @@ void ext4_add_complete_io(ext4_io_end_t *io_end) >> struct workqueue_struct *wq; >> unsigned long flags; >> >> - BUG_ON(!(io_end->flag & EXT4_IO_END_UNWRITTEN)); >> - wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq; >> + BUG_ON(!ext4_io_end_deferred(io_end)); >> + if (io_end->flag & EXT4_IO_END_UNWRITTEN) >> + wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq; >> + else >> + wq = EXT4_SB(io_end->inode->i_sb)->aio_dio_flush_wq; > Umm, I'd prefer if we used aio_dio_flush_wq when EXT4_IO_END_NEEDS_SYNC > is set. That way slow syncing works will be always offloaded to a separate > workqueue. OK. Thanks! Jeff