From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [patch 0/6] Guest page hinting version 7. Date: Thu, 02 Apr 2009 13:34:37 -0700 Message-ID: <49D5215D.6050503@goop.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <49D51CA9.6090601@redhat.com> Sender: owner-linux-mm@kvack.org 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 List-Id: virtualization@lists.linuxfoundation.org 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, 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