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Subject: Re: [PATCH 14/18] writeback: control dirty pause time
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
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        Vivek Goyal <vgoyal@redhat.com>, Andrea Righi <arighi@develer.com>,
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Date: Mon, 12 Sep 2011 12:28:05 +0200
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On Wed, 2011-09-07 at 10:02 +0800, Wu Fengguang wrote:
> > also, do the two other line segments connect on the transition
> > point?
> 
> I guess we can simply unify the other two formulas into one:
> 
>         } else if (period <= max_pause / 4 &&
>                  pages_dirtied >= current->nr_dirtied_pause) {
>                 current->nr_dirtied_pause = clamp_val(
> ==>                                     dirty_ratelimit * (max_pause / 2) / HZ,
>                                         pages_dirtied + pages_dirtied / 8,
>                                         pages_dirtied * 4);
>         } else if (pause >= max_pause) {
>                 current->nr_dirtied_pause = 1 | clamp_val(
> ==>                                     dirty_ratelimit * (max_pause / 2) / HZ,
>                                         pages_dirtied / 4,
>                                         pages_dirtied - pages_dirtied / 8);
>         } 


There's still the clamping, that combined with the various conditionals
make it very hard to tell if the functions are connected or jump around.