linux-kernel - Re: [dm-devel] [PATCH] Fix over-zealous flush

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Date:	Mon, 07 Mar 2011 10:46:58 -0600
From:	James Bottomley <James.Bottomley@...e.de>
To:	device-mapper development <dm-devel@...hat.com>
Cc:	NeilBrown <neilb@...e.de>, Jens Axboe <axboe@...nel.dk>,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [dm-devel] [PATCH] Fix over-zealous flush_disk when changing
 device size.

On Sun, 2011-03-06 at 21:22 -0700, Andrew Patterson wrote:
> On Sun, 2011-03-06 at 17:47 +1100, NeilBrown wrote:
> >  Would you be uncomfortable if I asked Linus to revert both my fix and your
> >  original patch??
> 
> James Bottomley wanted me to put this functionality in. I have no
> problem with reverting it myself, especially if it is causing other
> problems.  I would have to say that you need to ask him (or rather, I am
> not qualified to render an opinion here).

So it seems we have a couple of problems: the first being that
flush_disk() doesn't actually do what it says (flush the disk).  If it's
just discarding all data, dirty or clean, then its use in the
grow/shrink interface is definitely wrong.

The idea is that before we complete the grow/shrink, we make sure that
the device doesn't have any errors, so we want to try to write out all
dirty buffers to make sure they still have a home.  If flush_disk()
doesn't do that, then we need to use a different interface ... what's
the interface to flush a disk?

James

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