linux-kernel - Re: Device loses barrier support (was: Fixed patch for simple barriers.)

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Date:	Fri, 5 Dec 2008 01:48:49 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	xfs@....sgi.com, Alasdair G Kergon <agk@...hat.com>,
	Andi Kleen <andi-suse@...stfloor.org>,
	Milan Broz <mbroz@...hat.com>
Subject: Re: Device loses barrier support (was: Fixed patch for simple barriers.)

> And if barriers fail at random points, the user can't turn on disk cache 
> anyway (he would get data corruption if barrier write failed and hardware 

I think we already established earlier in the thread that there is no disk
corruption

> > > I'm wondering, where in fsync() does Linux wait for hardware disk cache to 
> > > be flushed? Isn't there a bug that fsync() will return before the cache is 
> > > flushed? I couldn't really find it. The last thing do_fsync calls is 
> > > filemap_fdatawait and it doesn't do cache flush (blkdev_issue_flush).
> > 
> > At least in fsync() on journaling fs the metadata update should push it.
> > 
> > -Andi
> 
> And what about fdatasync()?

I don't know. The surest way to find out is to instrument it and try.

-Andi
-- 
ak@...ux.intel.com
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