From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 5 Mar 2007 17:01:43 +0100 From: Nick Piggin Subject: Re: The performance and behaviour of the anti-fragmentation related patches Message-ID: <20070305160143.GB8128@wotan.suse.de> References: <20070301101249.GA29351@skynet.ie> <20070301160915.6da876c5.akpm@linux-foundation.org> <45E8594B.6020904@austin.ibm.com> <20070305032116.GA29678@wotan.suse.de> <45EC352A.7060802@austin.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <45EC352A.7060802@austin.ibm.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Joel Schopp Cc: Linus Torvalds , Andrew Morton , Mel Gorman , clameter@engr.sgi.com, mingo@elte.hu, arjan@infradead.org, mbligh@mbligh.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Mon, Mar 05, 2007 at 09:20:10AM -0600, Joel Schopp wrote: > >But if you don't require a lot of higher order allocations anyway, then > >guest fragmentation caused by ballooning doesn't seem like much problem. > > If you only need to allocate 1 page size and smaller allocations then no > it's not a problem. As soon as you go above that it will be. You don't > need to go all the way up to MAX_ORDER size to see an impact, it's just > increasingly more severe as you get away from 1 page and towards MAX_ORDER. We allocate order 1 and 2 pages for stuff without too much problem. > >If you need higher order allocations, then ballooning is bad because of > >fragmentation, so you need memory unplug, so you need higher order > >allocations. Goto 1. > > Yes, it's a closed loop. But hotplug isn't the only one that needs higher > order allocations. In fact it's pretty far down the list. I look at it > like this, a lot of users need high order allocations for better > performance and things like on-demand hugepages. As a bonus you get memory > hot-remove. on-demand hugepages could be done better anyway by having the hypervisor defrag physical memory and provide some way for the guest to ask for a hugepage, no? > >Balooning probably does skew memory management stats and watermarks, but > >that's just because it is implemented as a module. A couple of hooks > >should be enough to allow things to be adjusted? > > That is a good idea independent of the current discussion. Well it shouldn't be too difficult. If you cc linux-mm and/or me with any thoughts or requirements then I could try to help with it. Thanks, Nick -- 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