|| ||Linus Torvalds <torvalds-AT-linux-foundation.org>|
|| ||Balbir Singh <balbir-AT-in.ibm.com>|
|| ||Re: The performance and behaviour of the anti-fragmentation related
|| ||Thu, 1 Mar 2007 19:44:27 -0800 (PST)|
|| ||Andrew Morton <akpm-AT-linux-foundation.org>,
Mel Gorman <mel-AT-skynet.ie>, npiggin-AT-suse.de,
clameter-AT-engr.sgi.com, mingo-AT-elte.hu, jschopp-AT-austin.ibm.com,
arjan-AT-infradead.org, mbligh-AT-mbligh.org, linux-mm-AT-kvack.org,
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.
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
> 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.
In other words, I really don't see a huge upside. I see *lots* of
downsides, but upsides? Not so much. Almost everybody who wants unplug
wants virtualization, and right now none of the "big virtualization"
people would want to have kernel-level anti-fragmentation anyway sicne
they'd need to do it on their own.
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