Re: [Xen-devel] [PATCH v5 5/8] xen: double default grant frame limit for huge hosts

[Juergen Gross <jgross@xxxxxxxx>]

On 08/09/17 17:48, Jan Beulich wrote:
>>>> On 08.09.17 at 08:56, <jgross@xxxxxxxx> wrote:
>> --- a/xen/common/grant_table.c
>> +++ b/xen/common/grant_table.c
>> @@ -3824,8 +3824,15 @@ static int __init gnttab_usage_init(void)
>>  {
>>      BUILD_BUG_ON(DEFAULT_MAX_MAPTRACK_FRAMES < DEFAULT_MAX_NR_GRANT_FRAMES);
>>  
>> +    /*
>> +     * In case grant v2 is required for pv domains to reference any possible
>> +     * memory page (i.e. memory is installed above 16TB boundary) double the
>> +     * grant frame limit. This will allow a guest using v2 grants without
>> +     * having to lower the number of usable grants.
>> +     */
>>      if ( !max_grant_frames )
>> -        max_grant_frames = DEFAULT_MAX_NR_GRANT_FRAMES;
>> +        max_grant_frames = ((max_page >> 32) ? 2 : 1) *
>> +                           DEFAULT_MAX_NR_GRANT_FRAMES;
> 
> Didn't we agree that HVM domains exceeding 16Tb (or even only
> placing any GFNs above the 16Tb boundary) would also need to
> make use of v2? If so, please drop the reference to PV or add
> half a sentence for HVM. Dropping may be better as this is
> common code, and ARM doesn't make that distinction.

Oh, sorry. Will drop the PV reference.


Juergen


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