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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>
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@ -1233,6 +1233,7 @@ static void task_numa_placement(struct task_struct *p)
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{
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int seq, nid, max_nid = -1, max_group_nid = -1;
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unsigned long max_faults = 0, max_group_faults = 0;
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spinlock_t *group_lock = NULL;
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seq = ACCESS_ONCE(p->mm->numa_scan_seq);
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if (p->numa_scan_seq == seq)
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@ -1241,6 +1242,12 @@ static void task_numa_placement(struct task_struct *p)
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p->numa_migrate_seq++;
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p->numa_scan_period_max = task_scan_max(p);
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/* If the task is part of a group prevent parallel updates to group stats */
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if (p->numa_group) {
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group_lock = &p->numa_group->lock;
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spin_lock(group_lock);
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}
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/* Find the node with the highest number of faults */
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for_each_online_node(nid) {
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unsigned long faults = 0, group_faults = 0;
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@ -1279,20 +1286,24 @@ static void task_numa_placement(struct task_struct *p)
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}
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}
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/*
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* If the preferred task and group nids are different,
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* iterate over the nodes again to find the best place.
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*/
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if (p->numa_group && max_nid != max_group_nid) {
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unsigned long weight, max_weight = 0;
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if (p->numa_group) {
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/*
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* If the preferred task and group nids are different,
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* iterate over the nodes again to find the best place.
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*/
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if (max_nid != max_group_nid) {
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unsigned long weight, max_weight = 0;
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for_each_online_node(nid) {
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weight = task_weight(p, nid) + group_weight(p, nid);
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if (weight > max_weight) {
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max_weight = weight;
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max_nid = nid;
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for_each_online_node(nid) {
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weight = task_weight(p, nid) + group_weight(p, nid);
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if (weight > max_weight) {
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max_weight = weight;
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max_nid = nid;
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}
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}
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}
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spin_unlock(group_lock);
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}
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/* Preferred node as the node with the most faults */
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