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

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Message-Id: <20111013143501.a59efa5c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 13 Oct 2011 14:35:01 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Satoru Moriya <satoru.moriya@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Satoru Moriya <smoriya@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"lwoodman@...hat.com" <lwoodman@...hat.com>,
	Seiji Aguchi <saguchi@...hat.com>,
	Hugh Dickins <hughd@...gle.com>, hannes@...xchg.org
Subject: Re: [PATCH -v2 -mm] add extra free kbytes tunable

On Wed, 12 Oct 2011 17:01:21 -0700 (PDT)
David Rientjes <rientjes@...gle.com> wrote:

> On Wed, 12 Oct 2011, Satoru Moriya wrote:

> > I understand what you concern. But in some area such as banking,
> > stock exchange, train/power/plant control sysemts etc this kind
> > of tunable is welcomed because they can tune their systems at
> > their own risk.
> > 
> 
> You haven't tried the patch that increases the priority of kswapd when 
> such a latency sensitive thread triggers background reclaim?

I don't read full story but....how about adding a new syscall like

==
sys_mem_shrink(int nid, int nr_scan_pages, int flags)

This system call scans LRU of specified nodes and free pages on LRU.
This scan nr_scan_pages in LRU and returns the number of successfully
freed pages.
==

Then, running this progam in SCHED_IDLE, a user can make free pages while
the system is idle. If running in the highest priority, a user can keep
free pages as he want. If a user run this under a memcg, user can free
pages in a memcg. 

Maybe many guys don't want to export memory-shrink facility to userland ;)
This is just an idea.

Thanks,
-Kame

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