Re: [RFC] [PATCH] A clean aEvgeniy pproach to writeout throttling

From: Daniel Phillips <phillips@phunq.net>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC] [PATCH] A clean aEvgeniy pproach to writeout throttling
Date: Mon, 10 Dec 2007 03:23:48 -0800	[thread overview]
Message-ID: <200712100323.48535.phillips@phunq.net> (raw)
In-Reply-To: <20071210104749.GC5008@kernel.dk>

On Monday 10 December 2007 02:47, Jens Axboe wrote:
> Ehm, this patch is so broken it's not even funny - did you even
> compile? You would have noticed the warning on request_queue_t,
> surely. The big problem is the last hunk here though, how would that
> work on stacked devices? Clue: ->bi_bdev is not const, it can change
> after a call to ->make_request_fn().

Such paranoia.  Yes, the patch was compiled.   Yes, the warning was 
slipped through.  No, it is not substantive, and in fact was removed 
from another branch of our tree already.

Ignoring the rhetoric, apparently you missed the line:

+       if (q && q->metric && !bio->bi_queue) {

The prevents any reference ti bi_bdev after the intial call to 
generic_make_request.  Thanks to Evgeniy for pointing out the need for 
this measure on the last go round.

"So broken" is a gross exaggeration.  Substantive comments welcome.

Daniel