linux-kernel - Re: Queue upcall locking (was: [dm-devel] [RFC][PATCH] fix dm_any_congested() to properly sync up with suspend code path)

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Message-ID: <20081110142715.GD16649@agk.fab.redhat.com>
Date:	Mon, 10 Nov 2008 14:27:15 +0000
From:	Alasdair G Kergon <agk@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Mikulas Patocka <mpatocka@...hat.com>, axboe@...nel.dk,
	dm-devel <dm-devel@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: Queue upcall locking (was: [dm-devel] [RFC][PATCH] fix dm_any_congested() to properly sync up with suspend code path)

On Mon, Nov 10, 2008 at 08:54:01AM -0500, Christoph Hellwig wrote:
> On Mon, Nov 10, 2008 at 08:11:51AM -0500, Mikulas Patocka wrote:
> > For upstream Linux developers: you are holding a spinlock and calling 
> > bdi*_congested functions that can take indefinite amount of time (there 
> > are even users reporting having 50 disks in one logical volume or so). I 
> > think it would be good to move these calls out of spinlocks.
> Umm, they shouldn't block that long, as that completely defeats their
> purpose.  

Indeed - the blocking was a bug for which there's a patch, but that doesn't
deal with how the function should be operating in the first place.

- If one device is found to be congested, why bother checking the remaining
devices?

- If the device is suspended, the response should be that it is congested, I'd
have thought.

Alasdair
-- 
agk@...hat.com
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