From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH 3/6] xen-gntdev: Remove unneeded structures
	from	grant_map tracking data
Date: Tue, 14 Dec 2010 13:54:55 -0800
Message-ID: <4D07E7AF.7000101@goop.org>
References: <1292338553-20575-1-git-send-email-dgdegra@tycho.nsa.gov>
	<1292338553-20575-4-git-send-email-dgdegra@tycho.nsa.gov>
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To: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Cc: Isaku Yamahata <yamahata@valinux.co.jp>, xen-devel@lists.xensource.com, Ian.Campbell@citrix.com
List-Id: xen-devel@lists.xenproject.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