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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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