Re: [Xen-devel] [PATCH for-4.13 2/2] Rationalize max_grant_frames and max_maptrack_frames handling

[Jürgen Groß <jgross@xxxxxxxx>]

On 26.11.19 18:30, George Dunlap wrote:
> On 11/26/19 5:17 PM, George Dunlap wrote:
> > - xl will use the libxl default for maptrack, but does its own default
> >    calculation for grant frames: either 32 or 64, based on the max
> >    possible mfn.
> [snip]
>
> > @@ -199,13 +198,6 @@ static void parse_global_config(const char *configfile,
> >   
> >       if (!xlu_cfg_get_long (config, "max_grant_frames", &l, 0))
> >           max_grant_frames = l;
> > -    else {
> > -        libxl_physinfo_init(&physinfo);
> > -        max_grant_frames = (libxl_get_physinfo(ctx, &physinfo) != 0 ||
> > -                            !(physinfo.max_possible_mfn >> 32))
> > -                           ? 32 : 64;
> > -        libxl_physinfo_dispose(&physinfo);
> > -    }
> Sorry, meant to add a patch to add this functionality back into the
> hypervisor -- i.e., so that opt_max_grant_frames would be 32 on systems
> with 32-bit mfns.
>
> But this seems like a fairly strange calculation anyway; it's not clear
> to me where it would have come from.
mfns above the 32-bit limit require to use grant v2. This in turn
doubles the grant frames needed for the same number of grants.


Juergen


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