linux-kernel - Re: [PATCH 2/5] writeback: dirty position control

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Message-ID: <1313154504.6576.44.camel@twins>
Date:	Fri, 12 Aug 2011 15:08:24 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	Greg Thelen <gthelen@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Andrea Righi <arighi@...eler.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] writeback: dirty position control

On Fri, 2011-08-12 at 20:59 +0800, Wu Fengguang wrote:
> On Fri, Aug 12, 2011 at 08:54:17PM +0800, Peter Zijlstra wrote:
> > On Fri, 2011-08-12 at 00:56 +0200, Peter Zijlstra wrote:
> > > 
> > >                s - x 3
> > >  f(x) :=  1 + (-----)
> > >                  d
> > > 
> > btw, if you want steeper slopes for rampup and brake you can add another
> > factor like:
> > 
> >                  s - x 3
> >   f(x) :=  1 + a(-----)
> >                    d
> >  
> > And solve the whole f(l)=0 thing again to determine d in l and a.
> > 
> > For 0 < a < 1 the slopes increase.
> 
> Yes, we can leave it as a future tuning option. For now I'm pretty
> satisfied with the current function's shape :)

Oh for sure, it just occurred to me when looking at your plots and
thought I'd at least mention it.. You know something to poke at on a
rainy afternoon ;-)
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