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



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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