From: Ted Ts'o <tytso@mit.edu>
To: Jan Kara <jack@suse.cz>
Cc: Ext4 Developers List <linux-ext4@vger.kernel.org>
Subject: Re: [PATCH] ext4: fake direct I/O mode for data=journal
Date: Mon, 15 Aug 2011 14:03:11 -0400 [thread overview]
Message-ID: <20110815180311.GC5948@thunk.org> (raw)
In-Reply-To: <20110815115939.GA6971@quack.suse.cz>
On Mon, Aug 15, 2011 at 01:59:39PM +0200, Jan Kara wrote:
> Why have you chosen to set O_DSYNC?
O_DSYNC was the closest thing to O_DIRECT, in that writes get forced
to disk after the write finished. I did this fix a test failure
caused by missing direct I/O writes with a buffered read. OTOH, there
is a performance cost in doing this since it will force a journal
commit after every write. That's probably not acceptable. Hmph.
> Also what about reads? Mixing of buffered writes and direct IO reads will
> not work because filemap_write_and_write() does not write data block to the
> final location on disk but only to a journal.
Given that, we're probably better off forcing reads drop O_DIRECT as
well and drop O_DSYNC.
I'll change the patch and then give it a test.
- Ted
next prev parent reply other threads:[~2011-08-15 18:03 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-15 2:19 [PATCH] ext4: fake direct I/O mode for data=journal Theodore Ts'o
2011-08-15 11:59 ` Jan Kara
2011-08-15 18:03 ` Ted Ts'o [this message]
2011-08-16 19:32 ` [PATCH -v2] " Theodore Ts'o
2011-08-17 11:42 ` Jan Kara
2011-08-17 16:50 ` Ted Ts'o
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