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

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Date:	Sun, 23 Oct 2011 14:22:22 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Satoru Moriya <satoru.moriya@....com>
cc:	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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 Fri, 21 Oct 2011, Satoru Moriya wrote:

> We do.
> Basically we need this kind of feature for almost all our latency
> sensitive applications to avoid latency issue in memory allocation.
> 

These are all realtime?

> Currently we run those applications on custom kernels which this
> kind of patch is applied to. But it is hard for us to support every
> kernel version for it. Also there are several customers who can't
> accept a custom kernel and so they must use other commercial Unix.
> If this feature is accepted, they will definitely use it on their
> systems.
> 

That's precisely the problem, it's behavior is going to vary widely from 
version to version as the implementation changes for reclaim and 
compaction.  I think we can do much better with the priority of kswapd and 
reclaiming above the high watermark for threads that need a surplus of 
extra memory because they are realtime, two things we can easily do.
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