Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 7dbd13ed authored by Mel Gorman's avatar Mel Gorman Committed by Ingo Molnar
Browse files

sched/numa: Prevent parallel updates to group stats during placement 



Having multiple tasks in a group go through task_numa_placement
simultaneously can lead to a task picking a wrong node to run on, because
the group stats may be in the middle of an update. This patch avoids
parallel updates by holding the numa_group lock during placement
decisions.

Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-52-git-send-email-mgorman@suse.de


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 82727018

kernel/sched/fair.c

+23 −12
Original line number Diff line number Diff line
@@ -1233,6 +1233,7 @@ static void task_numa_placement(struct task_struct *p) 
{

	int seq, nid, max_nid = -1, max_group_nid = -1;

	unsigned long max_faults = 0, max_group_faults = 0;

	spinlock_t *group_lock = NULL;



	seq = ACCESS_ONCE(p->mm->numa_scan_seq);

	if (p->numa_scan_seq == seq)
@@ -1241,6 +1242,12 @@ static void task_numa_placement(struct task_struct *p) 
	p->numa_migrate_seq++;

	p->numa_scan_period_max = task_scan_max(p);



	/* If the task is part of a group prevent parallel updates to group stats */

	if (p->numa_group) {

		group_lock = &p->numa_group->lock;

		spin_lock(group_lock);

	}



	/* Find the node with the highest number of faults */

	for_each_online_node(nid) {

		unsigned long faults = 0, group_faults = 0;
@@ -1279,11 +1286,12 @@ static void task_numa_placement(struct task_struct *p) 
		}

	}



	if (p->numa_group) {

		/*

		 * If the preferred task and group nids are different,

		 * iterate over the nodes again to find the best place.

		 */

	if (p->numa_group && max_nid != max_group_nid) {

		if (max_nid != max_group_nid) {

			unsigned long weight, max_weight = 0;



			for_each_online_node(nid) {
@@ -1295,6 +1303,9 @@ static void task_numa_placement(struct task_struct *p) 
			}

		}



		spin_unlock(group_lock);

	}



	/* Preferred node as the node with the most faults */

	if (max_faults && max_nid != p->numa_preferred_nid) {

		/* Update the preferred nid and migrate task if possible */