Re: [PATCH 2/3] ext4: honor the O_SYNC flag for aysnchronous direct I/O requests
From: Jan Kara <jack@suse.cz>
Date: 2012-02-02 17:31:22
Also in:
linux-fsdevel, linux-xfs
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!
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Signed-off-by: Jeff Moyer <redacted> --- 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 ;)
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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 [off-list ref] SUSE Labs, CR