From: Jens Axboe <jens.axboe@oracle.com>
To: Daniel Phillips <phillips@phunq.net>
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 13:16:27 +0100 [thread overview]
Message-ID: <20071210121627.GF5008@kernel.dk> (raw)
In-Reply-To: <200712100413.38077.phillips@phunq.net>
On Mon, Dec 10 2007, Daniel Phillips wrote:
> On Monday 10 December 2007 03:41, Jens Axboe wrote:
> > On Mon, Dec 10 2007, Daniel Phillips wrote:
> > > + if (q && q->metric && !bio->bi_queue) {
> > >
> > > This prevents any reference to 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.
> >
> > Which saves the initial target, for ease of accounting at end io time
> > - that's not the point. What happens when ->make_request_fn() changes
> > bio->bi_bdev and returns 1, causing another iteration of the
> > __generic_make_request() loop? 'q' is no longer the valid target,
> > bdev_get_queue(bio->bi_bdev) is.
>
> What happens on the second iteration of a recursive submission loop is
> exactly nothing, as is right and proper. The throttling has already
> been done, and all the state necessary to perform the unthrottle was
> recorded in the bio. Everything seems to be in order there, and the
> algorithm does indeed perform its function as designed, though to be
> sure we have not tested it on -mm branch, only on mainline.
OK, let me get the neon out then. This has nothing to do with
throttling, I thought I made it clear that I get why you store the
origin queue in ->bi_queue. I'm concerned with the workings of
redirecting a bio. Previously we looked up the queue associated with
bio->bi_bdev inside the loop in __generic_make_request(), as is REQUIRED
to correctly locate a DIFFERENT queue if bio->bi_bdev has been changed
to point somewhere else.
Clear?
--
Jens Axboe
next prev parent reply other threads:[~2007-12-10 12:19 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-06 0:03 [RFC] [PATCH] A clean approach to writeout throttling Daniel Phillips
2007-12-06 1:24 ` Andrew Morton
2007-12-06 6:21 ` Daniel Phillips
2007-12-06 7:31 ` Andrew Morton
2007-12-06 9:48 ` Daniel Phillips
2007-12-06 11:55 ` Andrew Morton
2007-12-06 15:52 ` Rik van Riel
2007-12-06 17:34 ` Andrew Morton
2007-12-06 17:48 ` Rik van Riel
2007-12-06 20:04 ` Daniel Phillips
2007-12-06 20:27 ` Andrew Morton
2007-12-06 21:27 ` Daniel Phillips
2007-12-06 21:53 ` Bill Davidsen
2007-12-07 0:04 ` Daniel Phillips
2007-12-07 0:29 ` Andrew Morton
2007-12-07 7:13 ` Daniel Phillips
2007-12-10 9:20 ` Daniel Phillips
2007-12-10 10:47 ` Jens Axboe
2007-12-10 11:23 ` [RFC] [PATCH] A clean aEvgeniy pproach " Daniel Phillips
2007-12-10 11:41 ` Jens Axboe
2007-12-10 12:13 ` Daniel Phillips
2007-12-10 12:16 ` Jens Axboe [this message]
2007-12-10 12:27 ` Daniel Phillips
2007-12-10 12:32 ` Jens Axboe
2007-12-10 13:04 ` Daniel Phillips
2007-12-10 13:19 ` Jens Axboe
2007-12-10 13:26 ` Daniel Phillips
2007-12-10 13:30 ` Jens Axboe
2007-12-10 13:43 ` Daniel Phillips
2007-12-10 13:53 ` Jens Axboe
2007-12-10 14:17 ` Daniel Phillips
2007-12-11 13:15 ` Jens Axboe
2007-12-11 19:38 ` Daniel Phillips
2007-12-11 20:01 ` Jens Axboe
2007-12-11 20:11 ` Daniel Phillips
2007-12-11 20:07 ` Daniel Phillips
2007-12-10 11:33 ` [RFC] [PATCH] A clean approach " Daniel Phillips
2007-12-10 21:31 ` Jonathan Corbet
2007-12-10 22:06 ` Pekka Enberg
2007-12-11 4:21 ` Daniel Phillips
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