linux-kernel - Re: [PATCH -v2 -mm] add extra free kbytes tunable

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Message-Id: <20111011125419.2702b5dc.akpm@linux-foundation.org>
Date:	Tue, 11 Oct 2011 12:54:19 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Satoru Moriya <satoru.moriya@....com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Satoru Moriya <smoriya@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"lwoodman@...hat.com" <lwoodman@...hat.com>,
	Seiji Aguchi <saguchi@...hat.com>,
	"hughd@...gle.com" <hughd@...gle.com>,
	"hannes@...xchg.org" <hannes@...xchg.org>
Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable

On Tue, 11 Oct 2011 15:32:11 -0400
Satoru Moriya <satoru.moriya@....com> wrote:

> On 10/10/2011 06:37 PM, Andrew Morton wrote:
> > On Fri, 7 Oct 2011 20:08:19 -0700 (PDT) David Rientjes 
> > <rientjes@...gle.com> wrote:
> > 
> >> On Thu, 1 Sep 2011, Rik van Riel wrote:
> >
> > The page allocator already tries harder if the caller has 
> > rt_task(current).  Why is this inadequate?  Can we extend this idea 
> > further to fix whatever-the-problem-is?
> 
> Actually page allocator decreases min watermark to 3/4 * min watermark
> for rt-task. But in our case some applications create a lot of
> processes and if all of them are rt-task, the amount of watermark
> bonus(1/4 * min watermark) is not enough.
> 
> If we can tune the amount of bonus, it may be fine. But that is
> almost all same as extra free kbytes.

This situation is detectable at runtime.  If realtime tasks are being
stalled in the page allocator then start to increase the free-page
reserves.  A little control system.

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