Re: [PATCH 3/6] xen-gntdev: Remove unneeded structures from grant_map tracking data

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 12/14/2010 06:55 AM, Daniel De Graaf wrote:
> -static int unmap_grant_pages(struct grant_map *map, int offset, int pages)
> +static void unmap_grant_pages(struct grant_map *map, int offset, int pages)
>  {
> -	int i, err = 0;
> +	int i, flags, err = 0;
> +	struct gnttab_unmap_grant_ref *unmap_ops;
> +	struct gnttab_unmap_grant_ref unmap_single;
> +
> +	if (pages > 1) {
> +		unmap_ops = kzalloc(sizeof(unmap_ops[0]) * pages,
> +		                    GFP_TEMPORARY);
> +		if (unlikely(!unmap_ops)) {
> +			for(i=0; i < pages; i++)
> +				unmap_grant_pages(map, offset + i, 1);
> +			return;
> +		}
> +	} else {
> +		unmap_ops = &unmap_single;
> +	}

Rather than doing this, it would be better to use the multicall batching
API, in particular xen_mc_extend_args() - see xen_extend_mmu_update()
for an example.

(This would mean promoting arch/x86/xen/multicall.h to
include/xen/multicall.h and breaking ia64 builds until there's an ia64
implementation of that API, but that seems like a fair tradeoff at this
point.)

    J