From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 1 Mar 2007 19:44:27 -0800 (PST) From: Linus Torvalds Subject: Re: The performance and behaviour of the anti-fragmentation related patches In-Reply-To: <45E7835A.8000908@in.ibm.com> Message-ID: References: <20070301101249.GA29351@skynet.ie> <20070301160915.6da876c5.akpm@linux-foundation.org> <45E7835A.8000908@in.ibm.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Balbir Singh Cc: Andrew Morton , Mel Gorman , npiggin@suse.de, clameter@engr.sgi.com, mingo@elte.hu, jschopp@austin.ibm.com, arjan@infradead.org, mbligh@mbligh.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org