From: Jan Kara Subject: Re: [PATCH 2/3] ext4: honor the O_SYNC flag for aysnchronous direct I/O requests Date: Thu, 2 Feb 2012 18:31:20 +0100 Message-ID: <20120202173120.GA6640@quack.suse.cz> References: <1327698949-12616-1-git-send-email-jmoyer@redhat.com> <1327698949-12616-3-git-send-email-jmoyer@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org, xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org To: Jeff Moyer Return-path: Content-Disposition: inline In-Reply-To: <1327698949-12616-3-git-send-email-jmoyer@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Hi, On Fri 27-01-12 16:15:48, Jeff Moyer wrote: > If a file is opened with O_SYNC|O_DIRECT, the drive cache does not get > flushed after the write completion. Instead, it's flushed *before* the > I/O is sent to the disk (in __generic_file_aio_write). This patch > attempts to fix that problem by marking an I/O as requiring a cache > flush in endio processing. I'll send a follow-on patch to the > generic write code to get rid of the bogus generic_write_sync call > when EIOCBQUEUED is returned. Thanks for the patch! > Signed-off-by: Jeff Moyer > --- > fs/ext4/ext4.h | 4 ++++ > fs/ext4/inode.c | 11 +++++++++-- > fs/ext4/page-io.c | 39 ++++++++++++++++++++++++++++++++------- > fs/ext4/super.c | 11 +++++++++++ > 4 files changed, 56 insertions(+), 9 deletions(-) > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > index 2d55d7c..4377ed3 100644 > --- a/fs/ext4/ext4.h > +++ b/fs/ext4/ext4.h > @@ -185,6 +185,7 @@ struct mpage_da_data { > #define EXT4_IO_END_ERROR 0x0002 > #define EXT4_IO_END_QUEUED 0x0004 > #define EXT4_IO_END_DIRECT 0x0008 > +#define EXT4_IO_END_NEEDS_SYNC 0x0010 > > struct ext4_io_page { > struct page *p_page; > @@ -1247,6 +1248,9 @@ 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; > + Hmm, looking at the patch I'm wondering why did you introduce the new workqueue? It seems dio_unwritten_wq would be enough? You just need to rename it to something more appropriate ;) > diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c > index 9e1b8eb..d07cd40 100644 > --- a/fs/ext4/page-io.c > +++ b/fs/ext4/page-io.c > @@ -98,15 +98,40 @@ int ext4_end_io_nolock(ext4_io_end_t *io) > "list->prev 0x%p\n", > io, inode->i_ino, io->list.next, io->list.prev); > > - ret = ext4_convert_unwritten_extents(inode, offset, size); > - if (ret < 0) { > - ext4_msg(inode->i_sb, KERN_EMERG, > - "failed to convert unwritten extents to written " > - "extents -- potential data loss! " > - "(inode %lu, offset %llu, size %zd, error %d)", > - inode->i_ino, offset, size, ret); > + if (io->flag & EXT4_IO_END_UNWRITTEN) { > + > + ret = ext4_convert_unwritten_extents(inode, offset, size); > + if (ret < 0) { > + ext4_msg(inode->i_sb, KERN_EMERG, > + "failed to convert unwritten extents to " > + "written extents -- potential data loss! " > + "(inode %lu, offset %llu, size %zd, error %d)", > + inode->i_ino, offset, size, ret); > + goto endio; > + } > + } > + > + /* > + * This function has two callers. The first is the end_io_work > + * routine just below. This is an asynchronous completion context. > + * The second is in the fsync path. For the latter path, we can't > + * return from here until the job is done. Hence, we issue a > + * blocking blkdev_issue_flush call. > + */ > + if (io->flag & EXT4_IO_END_NEEDS_SYNC) { > + /* > + * Ideally, we'd like to know if the force_commit routine > + * actually did send something to disk. If it didn't, > + * then we need to issue the cache flush by hand. For now, > + * play it safe and do both. > + */ > + ret = ext4_force_commit(inode->i_sb); > + if (ret) > + goto endio; > + ret = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_NOIO, NULL); Look at what ext4_sync_file() does. It's more efficient than this. You need something like: commit_tid = file->f_flags & __O_SYNC ? EXT4_I(inode)->i_sync_tid : EXT4_I(inode)->i_datasync_tid; if (journal->j_flags & JBD2_BARRIER && !jbd2_trans_will_send_data_barrier(journal, commit_tid)) needs_barrier = true; jbd2_log_start_commit(journal, commit_tid); jbd2_log_wait_commit(journal, commit_tid); if (needs_barrier) blkdev_issue_flush(inode->i_sb->s_bdev, GFP_NOIO, NULL); Honza -- Jan Kara SUSE Labs, CR