Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762952AbZDBUev (ORCPT ); Thu, 2 Apr 2009 16:34:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756669AbZDBUem (ORCPT ); Thu, 2 Apr 2009 16:34:42 -0400 Received: from gw.goop.org ([64.81.55.164]:50714 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751147AbZDBUem (ORCPT ); Thu, 2 Apr 2009 16:34:42 -0400 Message-ID: <49D5215D.6050503@goop.org> Date: Thu, 02 Apr 2009 13:34:37 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Rik van Riel CC: Martin Schwidefsky , akpm@osdl.org, Nick Piggin , frankeh@watson.ibm.com, virtualization@lists.osdl.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-mm@kvack.org, hugh@veritas.com, Xen-devel Subject: Re: [patch 0/6] Guest page hinting version 7. References: <20090327150905.819861420@de.ibm.com> <200903281705.29798.rusty@rustcorp.com.au> <20090329162336.7c0700e9@skybase> <200904022232.02185.nickpiggin@yahoo.com.au> <20090402175249.3c4a6d59@skybase> <49D50CB7.2050705@redhat.com> <49D518E9.1090001@goop.org> <49D51CA9.6090601@redhat.com> In-Reply-To: <49D51CA9.6090601@redhat.com> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1677 Lines: 34 Rik van Riel wrote: > Jeremy Fitzhardinge wrote: >> The more complex host policy decisions of how to balance overall >> memory use system-wide are much in the same for both mechanisms. > Not at all. Page hinting is just an optimization to host swapping, where > IO can be avoided on many of the pages that hit the end of the LRU. > > No decisions have to be made at all about balancing memory use > between guests, it just happens through regular host LRU aging. When the host pages out a page belonging to guest A, then its making a policy decision on how large guest A should be compared to B. If the policy is a global LRU on all guest pages, then that's still a policy on guest sizes: the target size is a function of its working set, assuming that the working set is well modelled by LRU. I imagine that if the guest and host are both managing their pages with an LRU-like algorithm you'll get some nasty interactions, which page hinting tries to alleviate. > Automatic ballooning requires that something on the host figures > out how much memory each guest needs and sizes the guests > appropriately. All the proposed policies for that which I have > seen have some nasty corner cases or are simply very limited > in scope. Well, you could apply something equivalent to a global LRU: ask for more pages from guests who have the most unused pages. (I'm not saying that its necessarily a useful policy.) J -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/