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

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Date:	Fri, 02 Mar 2007 09:48:38 +0530
From:	Balbir Singh <balbir@...ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@...net.ie>, npiggin@...e.de,
	clameter@...r.sgi.com, mingo@...e.hu, jschopp@...tin.ibm.com,
	arjan@...radead.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

Linus Torvalds wrote:
> 
> On Fri, 2 Mar 2007, Balbir Singh wrote:
>>> My personal opinion is that while I'm not a huge fan of virtualization,
>>> these kinds of things really _can_ be handled more cleanly at that layer,
>>> and not in the kernel at all. Afaik, it's what IBM already does, and has
>>> been doing for a while. There's no shame in looking at what already works,
>>> especially if it's simpler.
>> Could you please clarify as to what "that layer" means - is it the
>> firmware/hardware for virtualization? or does it refer to user space?
> 
> Virtualization in general. We don't know what it is - in IBM machines it's 
> a hypervisor. With Xen and VMware, it's usually a hypervisor too. With 
> KVM, it's obviously a host Linux kernel/user-process combination.
> 

Thanks for clarifying.

> The point being that in the guests, hotunplug is almost useless (for 
> bigger ranges), and we're much better off just telling the virtualization 
> hosts on a per-page level whether we care about a page or not, than to 
> worry about fragmentation.
> 
> And in hosts, we usually don't care EITHER, since it's usually done in a 
> hypervisor.
> 
>> It would also be useful to have a resource controller like per-container
>> RSS control (container refers to a task grouping) within the kernel or
>> non-virtualized environments as well.
> 
> .. but this has again no impact on anti-fragmentation.
> 

Yes, I agree that anti-fragmentation and resource management are independent
of each other. I must admit to being a bit selfish here, in that my main
interest is in resource management and we would love to see a well
written  and easy to understand resource management infrastructure and 
controllers to control CPU and memory usage. Since the issue of
per-container RSS control came up, I wanted to ensure that we do not mix
up resource control and anti-fragmentation.

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