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Subject[PATCH 30/52] sched: Improve convergence
Date

- break out of can_do_numa_run() earlier if we can make no progress
- don't flip between siblings that often
- turn on bidirectional fault balancing
- improve the flow in task_numa_work()

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/fair.c | 46 ++++++++++++++++++++++++++++++++--------------
kernel/sched/features.h | 2 +-
2 files changed, 33 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 59fea2e..9c46b45 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -917,12 +917,12 @@ void task_numa_fault(int node, int last_cpu, int pages)
*/
void task_numa_work(struct callback_head *work)
{
+ long pages_total, pages_left, pages_changed;
unsigned long migrate, next_scan, now = jiffies;
+ unsigned long start0, start, end;
struct task_struct *p = current;
struct mm_struct *mm = p->mm;
struct vm_area_struct *vma;
- unsigned long start, end;
- long pages;

WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work));

@@ -951,35 +951,42 @@ void task_numa_work(struct callback_head *work)

current->numa_scan_period += jiffies_to_msecs(2);

- start = mm->numa_scan_offset;
- pages = sysctl_sched_numa_scan_size;
- pages <<= 20 - PAGE_SHIFT; /* MB in pages */
- if (!pages)
+ start0 = start = end = mm->numa_scan_offset;
+ pages_total = sysctl_sched_numa_scan_size;
+ pages_total <<= 20 - PAGE_SHIFT; /* MB in pages */
+ if (!pages_total)
return;

+ pages_left = pages_total;
+
down_write(&mm->mmap_sem);
vma = find_vma(mm, start);
if (!vma) {
ACCESS_ONCE(mm->numa_scan_seq)++;
- start = 0;
- vma = mm->mmap;
+ end = 0;
+ vma = find_vma(mm, end);
}
for (; vma; vma = vma->vm_next) {
if (!vma_migratable(vma))
continue;

do {
- start = max(start, vma->vm_start);
- end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);
+ start = max(end, vma->vm_start);
+ end = ALIGN(start + (pages_left << PAGE_SHIFT), HPAGE_SIZE);
end = min(end, vma->vm_end);
- pages -= change_prot_numa(vma, start, end);
- start = end;
- if (pages <= 0)
+ pages_changed = change_prot_numa(vma, start, end);
+
+ WARN_ON_ONCE(pages_changed > pages_total);
+ BUG_ON(pages_changed < 0);
+
+ pages_left -= pages_changed;
+ if (pages_left <= 0)
goto out;
} while (end != vma->vm_end);
}
out:
- mm->numa_scan_offset = start;
+ mm->numa_scan_offset = end;
+
up_write(&mm->mmap_sem);
}

@@ -3306,6 +3313,13 @@ static int select_idle_sibling(struct task_struct *p, int target)
int i;

/*
+ * For NUMA tasks constant, reliable placement is more important
+ * than flipping tasks between siblings:
+ */
+ if (task_numa_shared(p) >= 0)
+ return target;
+
+ /*
* If the task is going to be woken-up on this cpu and if it is
* already idle, then it is the right target.
*/
@@ -4581,6 +4595,10 @@ static bool can_do_numa_run(struct lb_env *env, struct sd_lb_stats *sds)
* If we got capacity allow stacking up on shared tasks.
*/
if ((sds->this_shared_running < sds->this_group_capacity) && sds->numa_shared_running) {
+ /* There's no point in trying to move if all are here already: */
+ if (sds->numa_shared_running == sds->this_shared_running)
+ return false;
+
env->flags |= LBF_NUMA_SHARED;
return true;
}
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index a432eb8..b75a10d 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -71,6 +71,6 @@ SCHED_FEAT(LB_MIN, false)
/* Do the working set probing faults: */
SCHED_FEAT(NUMA, true)
SCHED_FEAT(NUMA_FAULTS_UP, true)
-SCHED_FEAT(NUMA_FAULTS_DOWN, false)
+SCHED_FEAT(NUMA_FAULTS_DOWN, true)
SCHED_FEAT(NUMA_SETTLE, true)
#endif
--
1.7.11.7


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