linux-kernel - Re: [PATCH 3/7] numa,sched: build per numa_group active node mask from faults

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Message-ID: <52DD7129.3040106@redhat.com>
Date:	Mon, 20 Jan 2014 13:55:37 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	chegu_vinod@...com, mgorman@...e.de, mingo@...hat.com
Subject: Re: [PATCH 3/7] numa,sched: build per numa_group active node mask
 from faults_from statistics

On 01/20/2014 11:31 AM, Peter Zijlstra wrote:
> On Fri, Jan 17, 2014 at 04:12:05PM -0500, riel@...hat.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%.
>> + */
>> +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);
>> +	}
>> +}
> 
> Why not use 6/16 and 3/16 resp.? That avoids an actual division.

OK, will do.

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