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SubjectRe: 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
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