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

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Date:	Wed, 12 Oct 2011 17:01:21 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Satoru Moriya <satoru.moriya@....com>
cc:	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, Satoru Moriya wrote:

> > I think the point was that extra_free_kbytes needs to be tuned to 
> > cover at least the amount of memory of the largest allocation burst
> 
> Right. In enterprise area, we strictly test the system we build
> again and again before we release it. In that situation, we can
> set extra_free_kbytes appropriately based on system's requirements
> and/or specifications etc.
> 

You would also need to guarantee that min_free_kbytes isn't subsequently 
changed because that would change the value that extra_free_kbytes would 
need to preserve the same exclusive access to memory that the rt threads 
would have without increasing it.

> 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?
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