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

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Date:	Tue, 11 Oct 2011 15:32:11 -0400
From:	Satoru Moriya <satoru.moriya@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>
CC:	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 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.

> Does there exist anything like a test case which demonstrates the need 
> for this feature?

Unfortunately I don't have a real test case but just simple one.
And in my simple test case, I can avoid direct reclaim if we set
workload as rt-task.

The simple test case I used is following:
http://marc.info/?l=linux-mm&m=131605773321672&w=2

Regards,
Satoru
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