From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: PATCH reduce impact of FIFREEZE on userland processes
Date: Sat, 8 Dec 2012 07:12:04 -0500
Message-ID: <20121208121204.GA18467@infradead.org>
References: <20121205211707.7ca3b94b@aspire.ty-penguin.org.uk>
 <20121207004255.GC27172@dastard>
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Cc: Alun <alun.linux@ty-penguin.org.uk>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
To: Dave Chinner <david@fromorbit.com>
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On Fri, Dec 07, 2012 at 11:42:55AM +1100, Dave Chinner wrote:
> The problem wth doing this is that the sync can delay the freeze
> process by quite some time under the exact conditions you describe.
> If you want freeze to take effect immediately (i.e instantly stop
> new modifications), then adding a sync will break this semantic.
> THere are existing users of freeze that require this behaviour...

But that's only because he uses the big hammer sync_filesystem() which
actually waits for I/O completion.  I agree that this is a bad idea,
but if we'd just do a writeback_inodes_sb() call in this place that
starts asynchronous writeout I think everyone would benefit.