> -----Original Message----- > From: Jan Beulich <jbeul...@suse.com> > Sent: 20 November 2019 12:09 > To: Durrant, Paul <pdurr...@amazon.com> > Cc: Roger Pau Monné <roger....@citrix.com>; xen-devel@lists.xenproject.org > Subject: Re: [Xen-devel] grant table size > > On 20.11.2019 11:49, Durrant, Paul wrote: > >> From: Roger Pau Monné <roger....@citrix.com> > >> Sent: 20 November 2019 11:06 > >> > >> Do you have in mind to signal this somehow to guests, or the > >> expectation is that the guest will have to poll GNTTABOP_query_size > >> and at some point the size will increase? > > > > I don't think the guest need care until its grant table grows to the > > max. At that point, rather than giving up, the guest would re-query > > the max value to see if there is now more headroom and then re-size > > its internal data structures accordingly. > > If we consider dynamic adjustments, what about shrinking of the > table? This would of course require some form of guest consent, > but it would be nice if the option would at least be accounted > for when working out how all of this should behave, even if the > case may not get handled right now. >
Well, perhaps we could have a set_size gnttab op where a guest would be allowed to call it with a value less than (or equal to) its current max, so that it can voluntarily yield its headroom, but only a privileged guest would be allowed to call it with an increased max value? I'm not sure what mechanism would be best for requesting a guest reduction though, I guess probably xenstore... something akin to balloon target pages? A guest reduction of max is of pretty limited value though AFAICT as only in-use frames really use any memory. The (active/shared/status) arrays could, of course, be reduced in size but that only gets you a few bytes back. Paul _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
