From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: long latency of domain shutdown Date: Thu, 08 May 2008 13:11:21 +0100 Message-ID: References: <4822FC70.76E4.0078.0@novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4822FC70.76E4.0078.0@novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 8/5/08 12:13, "Jan Beulich" wrote: >> Nor am I convinced about how much potential time-saving >> there is to be had here. > > I'm not seeing any time saving here. The other thing I brought up > was just an unrelated item pointing out potential for code > simplification. Ah, yes, I see. The approach looks plausible. I think in its current form it will leave zombie L2/L3 pages hanging around and the domain will never actually properly die (e.g., still will be visible with the 'q' key). Because although you do get around to doing free_lX_table(), the type count and ref count of the L2/L3 pages will not drop to zero because the dead L3/L4 page never actually dropped its references properly. In actuality, since we know that we never have 'cross-domain' pagetable type references, we should actually be able to zap pagetable reference counts to zero. The only reason we don't do that right now is really because it provides good debugging info to see whether a domain's refcounts have got screwed up. But that would not prevent us doing something faster for NDEBUG builds, at least. Does that make sense? -- Keir