Re: [Xen-devel] [PATCH v2 5/8] xen: double default grant frame limit for huge hosts

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of
> Juergen Gross
> Sent: 06 September 2017 09:26
> To: xen-devel@xxxxxxxxxxxxx
> Cc: Juergen Gross <jgross@xxxxxxxx>; sstabellini@xxxxxxxxxx; Wei Liu
> <wei.liu2@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>;
> Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Ian Jackson
> <Ian.Jackson@xxxxxxxxxx>; Tim (Xen.org) <tim@xxxxxxx>;
> jbeulich@xxxxxxxx
> Subject: [Xen-devel] [PATCH v2 5/8] xen: double default grant frame limit for
> huge hosts
> 
> In case a system has memory above the 16TB boundary double the default
> grant frame number limit per domain. This ensures a pv domain can still
> establish the same number of grants even if it is required to use
> version 2 grants which need twice the space of v1 grants.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> ---
>  xen/common/grant_table.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
> index ae5f1262e8..709fd55490 100644
> --- 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;
> 
>      if ( !max_maptrack_frames )
>          max_maptrack_frames = DEFAULT_MAX_MAPTRACK_FRAMES;
> --
> 2.12.3
> 
> 
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