linux-kernel - Re: PATCH reduce impact of FIFREEZE on userland processes

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Message-ID: <20121208121204.GA18467@infradead.org>
Date:	Sat, 8 Dec 2012 07:12:04 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	Alun <alun.linux@...penguin.org.uk>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: PATCH reduce impact of FIFREEZE on userland processes

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.

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