linux-kernel - Re: [RFC PATCH] mm: let the bdi_writeout fraction respond more quickly

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Date:	Wed, 16 Jun 2010 20:54:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Richard Kennedy <richard@....demon.co.uk>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [RFC PATCH] mm: let the bdi_writeout fraction respond more
 quickly

On Mon, 2010-06-14 at 15:44 +0100, Richard Kennedy wrote:
> > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > index 2fdda90..315dd04 100644
> > --- a/mm/page-writeback.c
> > +++ b/mm/page-writeback.c
> > @@ -144,7 +144,7 @@ static int calc_period_shift(void)
> >       else
> >               dirty_total = (vm_dirty_ratio * determine_dirtyable_memory()) /
> >                               100;
> > -     return 2 + ilog2(dirty_total - 1);
> > +     return ilog2(dirty_total - 1) - 4;
> >  } 

IIRC I suggested similar things in the past and all we needed to do was
find people doing the measurements on different bits of hardware or so..

I don't have any problems with the approach, all we need to make sure is
that we never return 0 or a negative number (possibly ensure a minimum
positive shift value).


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