|From:||Linus Torvalds <torvalds-AT-linux-foundation.org>|
|To:||Balbir Singh <balbir-AT-in.ibm.com>|
|Subject:||Re: The performance and behaviour of the anti-fragmentation related patches|
|Date:||Thu, 1 Mar 2007 19:44:27 -0800 (PST)|
|Cc:||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, linux-kernel-AT-vger.kernel.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 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. 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. Linus
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