From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mick Jordan Subject: Re: Design question for PV superpage support Date: Mon, 02 Mar 2009 10:14:38 -0800 Message-ID: <49AC220E.9030000@Sun.COM> References: <200903020754.23534.dcm@mccr.org> <49AC0C96.7070608@Sun.COM> <49AC1B22.50307@Sun.COM> <200903021200.09999.dcm@mccr.org> Reply-To: Mick.Jordan@sun.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7BIT Return-path: In-reply-to: <200903021200.09999.dcm@mccr.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Dave McCracken Cc: Xen Developers List List-Id: xen-devel@lists.xenproject.org On 03/02/09 10:00, Dave McCracken wrote: > No, actually, it doesn't do that. The hypervisor allocates 2M pages, then > expands them into 4K pages for the mfn<->pfn maps, etc. > > The only effective difference is that any given 2M-aligned range of pfns is > guaranteed to map to a contiguous 2M-aligned range of mfns. Therefore the > guest can safely allocate 2M pages. > Ok. So I want to re-iterate my question from a previous post. After the patch allowing mixed mappings, what exactly went wrong on save/restore. And would my special case of 1-1 physival/virtual mappings with additional 2MB VM mappings adddress after domain start suffer in that case? From my (brief) experience, I think the problems of finding enough contiguous machine memory to allocate an all 2MB domain might be prohibitive. And when the memory is not fragmented I did not find it hard to "find" contiguous aligned 2MB machine pages even with the usual (seemingly random) pfn -> mfn mappings. It's a bit more code and runtime overhead, but it doesn't happen enough to worry about that. Mick