linux-ext4 - Re: [PATCH 2/3] ext4: honor the O_SYNC flag for aysnchronous direct I/O requests

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Message-ID: <x491uq51hsc.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 08 Feb 2012 10:11:47 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org, xfs@....sgi.com,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/3] ext4: honor the O_SYNC flag for aysnchronous direct I/O requests

Jan Kara <jack@...e.cz> writes:

>   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);

If the transaction won't send a data barrier, wouldn't you want to issue
the flush on the data device prior to commiting the transaction, not
after it?

-Jeff
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