>>> On 23.08.17 at 09:49, <jgr...@suse.com> wrote: > On 22/08/17 14:48, Jan Beulich wrote: >>>>> On 21.08.17 at 20:05, <jgr...@suse.com> wrote: >>> Currently Linux has no support for grant v2 as this would reduce the >>> maximum number of active grants by a factor of 2 compared to v1, >>> because the number of possible grants are limited by the allowed number >>> of grant frames and grant entries of v2 need twice as much bytes as >>> those of v1. >>> >>> Unfortunately grant v2 is the only way to support either guests with >>> more than 16TB memory size or PV guests with memory above the 16TB >>> border, as grant v1 limits the frame number to be 32 bits wide. >>> >>> In order to remove the disadvantage of grant v2 this patch series >>> enables configuring different maximum grant frame numbers for v1 and >>> v2. >> >> But that does imply higher memory footprint of such a guest in Xen, >> doesn't it? > > With current defaults this would need up to 128kB more for a guest using > v2 grants.
At least in an auto-ballooned setup this may make the difference between a guest being able or failing to start. >> The limit, after all, is there to bound resource use of >> DomU-s. I wonder whether we shouldn't make any such increase >> dependent on first putting in place proper accounting of the memory >> used for individual domains. > > So you would want to have a way to count pages (or bytes?) allocated for > hypervisor internal needs on a per-domain basis, right? > > Would that be additional to struct domain -> xenheap_pages or would you > want to merge the new counter into it? I guess a new field would be > required in order to avoid counting some data twice. > > Do you have an idea what to do with that value? Do you want to expose it > to the user (dom0 admin), or should it be used just inside the > hypervisor and e.g. printed by a debug key handler? > > Do you want an additional set of allocating functions doing the > accounting, or should the existing functions be used with an additional > domain pointer, or should the caller be responsible doing the additional > accounting? > > Do you want an all-or-nothing approach or a gradual move to add the new > accounting step by step? We've been vaguely discussing this in the past on a few occasions. My personal thinking is that the "memory=" setting in a guest config really ought to express all the memory associated with a guest. But of course there'll be problems with us starting to do so, and that's beyond people observing less memory in their guests. Switching to such a full accounting model will require some careful thought (and discussion up front). Hence I've only said "I wonder whether", i.e. I don't mean to make this a strict prerequisite to the proposed changes here. I'd be in particular interested to hear opinions of a few other people. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel