Re: [PATCH 3/7] numa,sched: build per numa_group active node mask from faults_from statistics

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Jan 17, 2014 at 04:12:05PM -0500, riel@redhat.com wrote:
>  /*
> + * Iterate over the nodes from which NUMA hinting faults were triggered, in
> + * other words where the CPUs that incurred NUMA hinting faults are. The
> + * bitmask is used to limit NUMA page migrations, and spread out memory
> + * between the actively used nodes. To prevent flip-flopping, and excessive
> + * page migrations, nodes are added when they cause over 40% of the maximum
> + * number of faults, but only removed when they drop below 20%.
> + */

Maybe break the above into two paragraphs for added readability.

Also, I think this might be a good spot to explain why you need the
second fault metric -- that is, why can't we create the interleave mask
from the existing memory location faults.

> +static void update_numa_active_node_mask(struct task_struct *p)
> +{
> +	unsigned long faults, max_faults = 0;
> +	struct numa_group *numa_group = p->numa_group;
> +	int nid;
> +
> +	for_each_online_node(nid) {
> +		faults = numa_group->faults_from[task_faults_idx(nid, 0)] +
> +			 numa_group->faults_from[task_faults_idx(nid, 1)];
> +		if (faults > max_faults)
> +			max_faults = faults;
> +	}
> +
> +	for_each_online_node(nid) {
> +		faults = numa_group->faults_from[task_faults_idx(nid, 0)] +
> +			 numa_group->faults_from[task_faults_idx(nid, 1)];
> +		if (!node_isset(nid, numa_group->active_nodes)) {
> +			if (faults > max_faults * 4 / 10)
> +				node_set(nid, numa_group->active_nodes);
> +		} else if (faults < max_faults * 2 / 10)
> +			node_clear(nid, numa_group->active_nodes);
> +	}
> +}

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