From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Need info on guest swapping and other things in KVM Date: Mon, 07 Apr 2008 07:08:57 +0300 Message-ID: <47F99E59.1030706@qumranet.com> References: <896ae46a0804041718i52fa31b9vfcdbb419edce79cc@mail.gmail.com> <47F87E1B.7050208@qumranet.com> <896ae46a0804061730v1d4c1d90mf25ea95bb2e56442@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel@lists.sourceforge.net To: Arjun Return-path: In-Reply-To: <896ae46a0804061730v1d4c1d90mf25ea95bb2e56442@mail.gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces@lists.sourceforge.net Errors-To: kvm-devel-bounces@lists.sourceforge.net List-Id: kvm.vger.kernel.org Please don't top-post. Arjun wrote: > Avi, > Thanks for your response. > > Regarding the query on "Guest Swapping", I'm referring to the > mechanism that the KVM host can use to swap out a guest's pages. Since > a guest OS will have its own swapping mechanism, then how will the > host ensure that if it choses to swap out a guest's page, it will not > conflict with the guest's own swapping mechanism. > Put another way: I understand (from docs, mailing list etc.) that KVM > allows the host to overbook/overcommit physical memory via the guest > swapping mechanism. i.e. the guest thinks it has x number of physical > pages but actually the host has swapped out some of the guests pages > and given the freed up physical memory to another guest VM. So the > guest actually has less than x pages in physical memory but doesn't > know it. > The guest and host swapping algorithms are completely independent. It is quite possible for the host to select an incorrect page (from a performance point of view) for swapping. There is a proposal (search for "CMM2") to allow cooperation between guest and host in this area. -- Any sufficiently difficult bug is indistinguishable from a feature. ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Register now and save $200. Hurry, offer ends at 11:59 p.m., Monday, April 7! Use priority code J8TLD2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone