From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: support for sharing huge pages with grant table? Date: Mon, 17 Nov 2014 10:34:47 +0000 Message-ID: <1416220487.27385.22.camel@citrix.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Tim Wood Cc: Xen devel list List-Id: xen-devel@lists.xenproject.org On Sun, 2014-11-16 at 23:39 -0500, Tim Wood wrote: > Hi, > > I am curious if Xen currently supports sharing hugepages between > domains (specifically ones originally allocated in Dom-0 and shared > with a guest r/w). I've seen some references to huge pages in the > archives of this list, but not in relation to the grant mechanism. I don't think the grant table has any specific superpage support. It might be an interesting extension to consider though (for the sorts of reasons you would like it). You could grant a superpage using multiple 4K grants to cover whichever subset of the superpage you need to expose to the other end. Now granted (no pun intended ;-)) that might suck up 512 grefs in the worst case, which is a bit mad... > Also, can someone confirm that "superpages" are another term for "huge > pages" in Xen? Yes. Or at least I think so. > This would be helpful for some work we are doing on high speed > networking to VMs---DPDK stores packets into huge pages and we'd like > to get those to VMs as quickly as possible. This seems like a reasonable usecase to me. Having added this to the grant table interface I suppose you would also need to consider extensions to the individual PV I/O protocols (netif.h) to allow them to signal when a grant was huge. You might have issues with e.g. finding enough bits to represent the larger sizes... Ian.