Re: [PATCH] allocate page caches pages in round robin fasion

[William Lee Irwin III <wli@holomorphy.com>]

On Thu, Aug 12, 2004 at 04:46:50PM -0700, Jesse Barnes wrote:
> +struct page *alloc_page_round_robin(unsigned int gfp_mask)
> +{
> +	return alloc_pages_node(__get_cpu_var(next_rr_node)++ % numnodes,
> +				gfp_mask, 0);
> +}
> +

Interesting. This may attempt to allocate from offlined nodes, assuming
one adds on sufficient hotplug bits atop mainline and/or -mm. The
following almost does it hotplug-safe except that it needs to enter the
allocator with preemption disabled and drop the preempt_count
internally to it.

static struct page *alloc_page_round_robin(unsigned gfp_mask)
{
	int nid, next_nid, *rr_node = &__get_cpu_var(next_rr_node);

	nid = *rr_node;
	next_nid = next_node(nid, node_online_map);
	if (next_nid >= MAX_NR_NODES)
		*rr_node = first_node(node_online_map);
	else
		*rr_node = next_nid;
	return alloc_pages_node(nid, gfp_mask, 0);
}

I suspect we are better off punting this in the direction of hotplug
people than trying to address it ourselves. I think we should go with
this now, as the node hotplug bits are yet to hit the tree.


-- wli