From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCH] libxl: create PVH guests with max memory assigned Date: Tue, 5 Aug 2014 10:34:48 +0100 Message-ID: <53E0A538.608@citrix.com> References: <1405594942-20760-1-git-send-email-roger.pau@citrix.com> <1407228940.2120.22.camel@kazak.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1XEb8v-00089C-MC for xen-devel@lists.xenproject.org; Tue, 05 Aug 2014 09:34:53 +0000 In-Reply-To: <1407228940.2120.22.camel@kazak.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: Ian Campbell , Roger Pau Monne Cc: xen-devel@lists.xenproject.org, Ian Jackson List-Id: xen-devel@lists.xenproject.org On 05/08/14 09:55, Ian Campbell wrote: > On Thu, 2014-07-17 at 13:02 +0200, Roger Pau Monne wrote: > > Sorry for the delay replying, this somehow slipped through my net. > >> Since PVH guests are very similar to HVM guests in terms of memory >> management, start the guest with the maximum memory assigned and let >> it balloon down. > > Both before and after this patch an HVM guest would be launched with > target_memkb though, not max_memkb (presumably relying on PoD), so the > comparison made in the commit log doesn't tally to me given that you are > making PVH (and only PVH) use max_memkb. > > This patch seems to make it impossible to boot a PVH guest > pre-ballooned. It only appears to "work" because I presume you actually > have enough RAM to satisfy maxmem for a short time, but that defeats the > purpose. > > Either a PVH guest is similar enough to an HVM guest in this area to > make use of PoD for early ballooning *or* it is similar enough to a PV > guest that it can use the PV kernel entry point to get in early enough > to initialise the balloon driver (via the XEN_EXTRA_MEM_MAX_REGIONS > stuff, I presume) before the kernels normal init sequence can start > mucking with that memory. A decision on which needs to be made and /documented/. If the PV-like approach is taken, I won't be accepting any Linux patches without such documentation. I now regret accepting the PVH support in Linux without a clear specification of what PVH actually is. David