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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: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik 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: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-52-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Mel Gorman 2013-10-07 11:29:29 +01:00 committed by Ingo Molnar
parent 82727018b0
commit 7dbd13ed06
1 changed files with 22 additions and 11 deletions
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33
kernel/sched/fair.c
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@ -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;
@ -1279,20 +1286,24 @@ static void task_numa_placement(struct task_struct *p)
}
}
/*
* 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) {
unsigned long weight, max_weight = 0;
if (p->numa_group) {
/*
* If the preferred task and group nids are different,
* iterate over the nodes again to find the best place.
*/
if (max_nid != max_group_nid) {
unsigned long weight, max_weight = 0;
for_each_online_node(nid) {
weight = task_weight(p, nid) + group_weight(p, nid);
if (weight > max_weight) {
max_weight = weight;
max_nid = nid;
for_each_online_node(nid) {
weight = task_weight(p, nid) + group_weight(p, nid);
if (weight > max_weight) {
max_weight = weight;
max_nid = nid;
}
}
}
spin_unlock(group_lock);
}
/* Preferred node as the node with the most faults */