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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Date:	Tue, 11 Nov 2008 13:18:54 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Chandra Seetharaman <sekharan@...ibm.com>,
	Alasdair G Kergon <agk@...hat.com>,
	dm-devel <dm-devel@...hat.com>, linux-kernel@...r.kernel.org,
	axboe@...nel.dk
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 09:19:21AM -0500, Mikulas Patocka wrote:
> For device mapper, congested_fn asks every device in the tree and make OR 
> of their bits --- so if the user has 50 devices, it asks them all.
> 
> For md-linear, md-raid0, md-raid1, md-raid10 and md-multipath it does the 
> same --- asking every device.
> 
> If you have a better idea how to implement congested_fn, say it.

Well, even asking 50 devices shouldn't take that long normally.  Do you
take some sleeping lock that might block forever?  In that case I would
just return congested for that device as it would delay pdflush
otherwise.

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