linux-kernel - Re: The performance and behaviour of the anti-fragmentation related patches

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Date:	Fri, 02 Mar 2007 07:09:31 +0530
From:	Balbir Singh <balbir@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Mel Gorman <mel@...net.ie>, npiggin@...e.de, clameter@...r.sgi.com,
	mingo@...e.hu, jschopp@...tin.ibm.com, arjan@...radead.org,
	torvalds@...ux-foundation.org, mbligh@...igh.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: The performance and behaviour of the anti-fragmentation related
 patches

Andrew Morton wrote:
> So some urgent questions are: how are we going to do mem hotunplug and
> per-container RSS?
> 
> 
> 
> Our basic unit of memory management is the zone.  Right now, a zone maps
> onto some hardware-imposed thing.  But the zone-based MM works *well*.  I
> suspect that a good way to solve both per-container RSS and mem hotunplug
> is to split the zone concept away from its hardware limitations: create a
> "software zone" and a "hardware zone".  All the existing page allocator and
> reclaim code remains basically unchanged, and it operates on "software
> zones".  Each software zones always lies within a single hardware zone. 
> The software zones are resizeable.  For per-container RSS we give each
> container one (or perhaps multiple) resizeable software zones.
> 
> For memory hotunplug, some of the hardware zone's software zones are marked
> reclaimable and some are not; DIMMs which are wholly within reclaimable
> zones can be depopulated and powered off or removed.
> 
> NUMA and cpusets screwed up: they've gone and used nodes as their basic
> unit of memory management whereas they should have used zones.  This will
> need to be untangled.
> 
> 
> Anyway, that's just a shot in the dark.  Could be that we implement unplug
> and RSS control by totally different means.  But I do wish that we'd sort
> out what those means will be before we potentially complicate the story a
> lot by adding antifragmentation.
> 

Paul Menage had suggested something very similar in response to the RFC
for memory controllers I sent out and it was suggested that we create
small zones (roughly 64 MB) to avoid the issue of a zone/node not being
a shareable across containers. Even with a small size, there are some 
issues. The following thread has the details discussed.

	http://lkml.org/lkml/2006/10/30/120

RSS accounting is very easy (with minimal changes to the core mm),
supplemented with an efficient per-container reclaimer, it should be
easy to implement a  good per-container RSS controller.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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