From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: what happens when a PoD page is touched? Date: Mon, 16 May 2011 11:05:20 +0100 Message-ID: References: <20110516083905.GP24068@whitby.uk.xensource.com> <291EDFCB1E9E224A99088639C4762022B37FC178F9@LONPMAILBOX01.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: James Harper Cc: Tim Deegan , Paul Durrant , xen devel List-Id: xen-devel@lists.xenproject.org On Mon, May 16, 2011 at 10:22 AM, James Harper wrote: > I've not seen any slowdown on boot with any version of Windows until I > go to actually do the balloon down... You mean, you don't see slowness on boot unless you boot with maxmem != memory (i.e,. in PoD mode)? For one thing, after the balloon driver is finished with its initial allocation, there shouldn't be any sweeping; if there is, then it may be that you're not actually inflating the balloon as much as Xen thinks you should. Before the balloon driver is done, the emergency sweep could be an issue. We had a bunch of stuff in XenServer in our most recent release to try to mitigate this, but it was all pretty hacky and unsuitable for upstreaming. I determined that it just needs to be re-written in a way that actually made things Better; I haven't gotten a chance to do that yet. It looks like ATM the sweep is limited to doing 2MiB at a time; so if you have a reasonably sized guest, every other superpage that gets hit will cause another sweep -- potentially a big problem. I have a patch that attempts to greedily re-grab pages after a sweep; I'll check to see if it applies to tip, and if so, I'll send it to you to see if that helps any. -George