* Mel Gorman <mgorman@xxxxxxx> [2013-07-03 15:21:38]:
> task_numa_placement checks current->mm but after buffers for faults
> have already been uselessly allocated. Move the check earlier.
>
> [peterz@xxxxxxxxxxxxx: Identified the problem]
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
> kernel/sched/fair.c | 22 ++++++++++++++--------
> 1 file changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 336074f..3c796b0 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -870,8 +870,6 @@ static void task_numa_placement(struct task_struct *p)
> int seq, nid, max_nid = 0;
> unsigned long max_faults = 0;
>
> - if (!p->mm) /* for example, ksmd faulting in a user's mm */
> - return;
> seq = ACCESS_ONCE(p->mm->numa_scan_seq);
> if (p->numa_scan_seq == seq)
> return;
> @@ -945,6 +943,12 @@ void task_numa_fault(int last_nid, int node, int pages, bool migrated)
> if (!sched_feat_numa(NUMA))
> return;
>
> + /* for example, ksmd faulting in a user's mm */
> + if (!p->mm) {
> + p->numa_scan_period = sysctl_numa_balancing_scan_period_max;
Naive question:
Why are we resetting the scan_period?
> + return;
> + }
> +
> /* Allocate buffer to track faults on a per-node basis */
> if (unlikely(!p->numa_faults)) {
> int size = sizeof(*p->numa_faults) * 2 * nr_node_ids;
> @@ -1072,16 +1076,18 @@ void task_numa_work(struct callback_head *work)
> end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);
> end = min(end, vma->vm_end);
> nr_pte_updates += change_prot_numa(vma, start, end);
> - pages -= (end - start) >> PAGE_SHIFT;
> -
> - start = end;
>
> /*
> * Scan sysctl_numa_balancing_scan_size but ensure that
> - * least one PTE is updated so that unused virtual
> - * address space is quickly skipped
> + * at least one PTE is updated so that unused virtual
> + * address space is quickly skipped.
> */
> - if (pages <= 0 && nr_pte_updates)
> + if (nr_pte_updates)
> + pages -= (end - start) >> PAGE_SHIFT;
> +
> + start = end;
> +
> + if (pages <= 0)
> goto out;
> } while (end != vma->vm_end);
> }
> --
> 1.8.1.4
>
--
Thanks and Regards
Srikar Dronamraju
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