On Wed, Nov 04, 2015 at 01:25:15PM -0500, Rik van Riel wrote:
> +++ b/kernel/sched/fair.c
> @@ -2155,6 +2155,7 @@ void task_numa_work(struct callback_head *work)
> unsigned long migrate, next_scan, now = jiffies;
> struct task_struct *p = current;
> struct mm_struct *mm = p->mm;
> + u64 runtime = p->se.sum_exec_runtime;
> struct vm_area_struct *vma;
> unsigned long start, end;
> unsigned long nr_pte_updates = 0;
> @@ -2277,6 +2278,20 @@ void task_numa_work(struct callback_head *work)
> else
> reset_ptenuma_scan(p);
> up_read(&mm->mmap_sem);
> +
> + /*
> + * There is a fundamental mismatch between the runtime based
> + * NUMA scanning at the task level, and the wall clock time
> + * NUMA scanning at the mm level. On a severely overloaded
> + * system, with very large processes, this mismatch can cause
> + * the system to spend all of its time in change_prot_numa().
> + * Limit NUMA PTE scanning to 3% of the task's run time, if
> + * we spent so much time scanning we got rescheduled.
> + */
> + if (unlikely(p->se.sum_exec_runtime != runtime)) {
> + u64 diff = p->se.sum_exec_runtime - runtime;
> + p->node_stamp += 32 * diff;
> + }
I don't actually see how this does what it says it does.
> }
>
> /*
> @@ -2302,7 +2317,7 @@ void task_tick_numa(struct rq *rq, struct task_struct
> *curr)
> now = curr->se.sum_exec_runtime;
> period = (u64)curr->numa_scan_period * NSEC_PER_MSEC;
>
> - if (now - curr->node_stamp > period) {
> + if (now > curr->node_stamp + period) {
> if (!curr->node_stamp)
> curr->numa_scan_period = task_scan_min(curr);
> curr->node_stamp += period;
And this really should be an independent patch. Although the fix I had
in mind looked like:
if ((s64)(now - curr->node_stamp) > period)
But I suppose this works too.
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