From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Xen 4.3 + tmem = Xen BUG at domain_page.c:143 Date: Wed, 12 Jun 2013 16:11:09 +0100 Message-ID: References: <51B881BD02000078000DD907@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51B881BD02000078000DD907@nat28.tlf.novell.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: Jan Beulich , George Dunlap , konrad wilk Cc: "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 12/06/2013 13:12, "Jan Beulich" wrote: >> What we see above is that this failure path succeeds three times, but >> fails the fourth time: there are, in fact, no zero entries after the >> garbage clean-up; however, because "inuse" is 32-bit (effectively) and >> "accum" is 64-bit, ~inuse always has bits 32-63 set, and so will >> always return true and never fall back to the "something else" > > Right, that's what occurred to me too yesterday, but the again > I knew I had seen this code path executed. Now that I look again, > I think I understand why: All of my Dom0-s and typical DomU-s > have a vCPU count divisible by 4, and with MAPCACHE_VCPU_ENTRIES > being 16, the full unsigned long would always be used. Why are we so tight on MAPCACHE_VCPU_ENTRIES? Why not say double that number and get rid of the accum and the 'replace a hash entry instead' logic instead? We never used to have it, and it's kind of extra complication and a bit gross. -- Keir