From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: Linux Xen Balloon Driver Improvement (Draft 2) Date: Mon, 27 Oct 2014 14:23:22 +0000 Message-ID: <544E555A.1000405@citrix.com> References: <20141027123328.GA9067@zion.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20141027123328.GA9067@zion.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Wei Liu , xen-devel@lists.xen.org Cc: Ian Campbell , Stefano Stabellini , Andrew Cooper , Dario Faggioli , David Vrabel , Boris Ostrovsky List-Id: xen-devel@lists.xenproject.org On 27/10/14 12:33, Wei Liu wrote: > > Changes in this version: > > 1. Style, grammar and typo fixes. > 2. Make this document Linux centric. > 3. Add a new section for NUMA-aware ballooning. You've not included the required changes to the toolstack and autoballoon driver to always use 2M multiples when creating VMs and setting targets. > ## Introduction > > This document describe a design to improve Xen balloon driver in Linux. "Linux balloon driver for Xen guests"? > ## Goal of improvement > > The balloon driver makes use of as many huge pages as possible, > defragmenting guest address space. Contiguous guest address space > permits huge page ballooning which helps prevent host address space > fragmentation. > > This should be achieved without any particular hypervisor side > feature. I really think you need to be taking whole-system view and not focusing on just the guest balloon driver. > ### Make use of balloon page compaction > > The core of migration callback is XENMEM\_exchange hypercall. This > makes sure that inflation of old page and deflation of new page is > done atomically, so even if a domain is beyond its memory target and > the target is being enforced, it can still compact memory. Having looked at what XENMEM_exchange actually does, I can't see how you're using it to give this behaviour. IMO, XEMMEM_exchange should probably be renamed XENMEM_repopulate or something. > ### Periodically exchange normal size pages with huge pages > > Worker thread wakes up periodically to check if there are enough pages > in normal size page queue to coalesce into a huge page. If so, it will > try to exchange that huge page into a number of normal size pages with > XENMEM\_exchange hypercall. I don't see what this is supposed to achieve. This is going to take a (potentially) non-fragmented superpage and fragment it. Your set of 512 4k ballooned pages needs to be ordered, contiguous and superpage aligned, for this to be any use. > ## Relationship with NUMA-aware ballooning > > Another orthogonal improvement to Linux balloon driver is NUMA-aware > ballooning. > > The use of balloon page compaction will not interfere with NUMA-ware > ballooning because balloon compaction, which is part of Linux's memory > subsystem, is already NUMA-aware. > > All the changes proposed in this design can be made NUMA-aware > provided virtual NUMA topology information is in place. How? David