linux-kernel - Re: [PATCH] Fix discard requests accounting in the diskstats

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Message-Id: <1239958751.3428.21.camel@macbook.infradead.org>
Date:	Fri, 17 Apr 2009 09:59:11 +0100
From:	David Woodhouse <david.woodhouse@...el.com>
To:	Nikanth Karthikesan <knikanth@...e.de>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jmarchan@...hat.com" <jmarchan@...hat.com>
Subject: Re: [PATCH] Fix discard requests accounting in the diskstats

On Fri, 2009-04-17 at 08:55 +0100, Nikanth Karthikesan wrote:
> On Friday 17 April 2009 12:19:12 Jens Axboe wrote:
> > On Fri, Apr 17 2009, Nikanth Karthikesan wrote:
> > > When 2 discard requests are merged, the stats gets updated, but we do not
> > > update statistics normally when a discard request is issued or completed.
> > > For example the in_flight counter would be decremented when 2 discard
> > > requests are merged, but it was not at all incremented when they were
> > > issued, and in_flight counter will not be decremented, when they are
> > > completed as well.
> > >
> > > This patch fixes this by adding discard requests to the statistics.
> >
> > This needs rebasing on top of this one:
> >
> > http://lkml.org/lkml/2009/4/16/159
> >
> > whenever that gets resubmitted as a proper, working patch.
> >
> 
> Ok. I will resend after Jerome resubmits that patch.

There are more interesting issues with discard requests and elevators
for now, such as the fact that elevators only actually prevent write
requests from crossing each other on the queue if the {start,end} range
precisely matches, not merely if they happen to overlap.

So all discard requests are submitted as soft barriers for now anyway.

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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