linux-ext4 - Re: [PATCH 3/3] Add timeout feature

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Message-ID: <20080708231026.GP11558@disturbed>
Date:	Wed, 9 Jul 2008 09:10:27 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Pavel Machek <pavel@...e.cz>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Takashi Sato <t-sato@...jp.nec.com>, akpm@...ux-foundation.org,
	viro@...IV.linux.org.uk,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"dm-devel@...hat.com" <dm-devel@...hat.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	axboe@...nel.dk, mtk.manpages@...glemail.com
Subject: Re: [PATCH 3/3] Add timeout feature

On Mon, Jul 07, 2008 at 01:07:31PM +0200, Pavel Machek wrote:
> Hi!
> 
> > I still disagree with this whole patch.  There is not reason to let
> > the freeze request timeout - an auto-unfreezing will only confuse the
> > hell out of the caller.  The only reason where the current XFS freeze
> > call can hang and this would be theoretically useful is when the
> 
> What happens when someone dirties so much data that vm swaps out
> whatever process that frozen the filesystem?

a) you can't dirty a frozen filesystem - by definition a frozen
   filesystem is a *clean filesystem* and *cannot be dirtied*.
b) Swap doesn't write through the filesystem
c) you can still read from a frozen filesystem to page your
   executableѕ in.
d) if dirtying another unfrozen filesystem swaps out your
   application so it can't run, then there's a major VM bug.
   Regardless, until the app completes it is relying on the
   filesystem being frozen, so it better remain frozen....

> I though that was why the timeout was there...

Not that I know of. 

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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