linux-kernel - Re: [PATCH 2/2] block: Convert BDI proportion calculations to flexible proportions

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Message-ID: <20120518142443.GA6875@quack.suse.cz>
Date:	Fri, 18 May 2012 16:24:43 +0200
From:	Jan Kara <jack@...e.cz>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/2] block: Convert BDI proportion calculations to
 flexible proportions

On Fri 18-05-12 00:04:33, Peter Zijlstra wrote:
> On Tue, 2012-05-15 at 17:43 +0200, Jan Kara wrote:
> > +static struct timer_list writeout_period_timer =
> > +               TIMER_DEFERRED_INITIALIZER(writeout_period, 0, 0); 
> 
> So the problem with using a deferred timer is that it 'ignores' idle
> time. So if a very busy period is followed by a real quiet period you'd
> expect all the proportions to have aged to 0, but they won't have.
  Ah, I see. Thanks for warning me.

> One way to solve that is to track a jiffies count of the last time the
> timer triggered and compute the missed periods from that and extend
> fprop_new_period() to deal with period increments of more than 1.
  Yeah, that should be easy enough so I'll try it that way since I presume
it's nicer to power usage to use deferred timers if it's reasonably
possible.

									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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