sched, numa, mm: Count WS scanning against present PTEs, not virtual memory ranges

By accounting against the present PTEs, scanning speed reflects the
actual present (mapped) memory.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>

1 files changed, 21 insertions, 15 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0a349dd1fa6..f6e1f25ed2b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -827,8 +827,8 @@ void task_numa_work(struct callback_head *work)
         struct task_struct *p = current;
         struct mm_struct *mm = p->mm;
         struct vm_area_struct *vma;
-        unsigned long offset, end;
-        long length;
+        unsigned long start, end;
+        long pages;
 
         WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work));
 
@@ -858,18 +858,20 @@ void task_numa_work(struct callback_head *work)
         if (cmpxchg(&mm->numa_next_scan, migrate, next_scan) != migrate)
                 return;
 
-        offset = mm->numa_scan_offset;
-        length = sysctl_numa_balancing_scan_size;
-        length <<= 20;
+        start = mm->numa_scan_offset;
+        pages = sysctl_numa_balancing_scan_size;
+        pages <<= 20 - PAGE_SHIFT; /* MB in pages */
+        if (!pages)
+                return;
 
         down_read(&mm->mmap_sem);
-        vma = find_vma(mm, offset);
+        vma = find_vma(mm, start);
         if (!vma) {
                 reset_ptenuma_scan(p);
-                offset = 0;
+                start = 0;
                 vma = mm->mmap;
         }
-        for (; vma && length > 0; vma = vma->vm_next) {
+        for (; vma; vma = vma->vm_next) {
                 if (!vma_migratable(vma))
                         continue;
 
@@ -877,15 +879,19 @@ void task_numa_work(struct callback_head *work)
                 if (((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) < HPAGE_PMD_NR)
                         continue;
 
-                offset = max(offset, vma->vm_start);
-                end = min(ALIGN(offset + length, HPAGE_SIZE), vma->vm_end);
-                length -= end - offset;
-
-                change_prot_numa(vma, offset, end);
+                do {
+                        start = max(start, vma->vm_start);
+                        end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);
+                        end = min(end, vma->vm_end);
+                        pages -= change_prot_numa(vma, start, end);
 
-                offset = end;
+                        start = end;
+                        if (pages <= 0)
+                                goto out;
+                } while (end != vma->vm_end);
         }
 
+out:
         /*
          * It is possible to reach the end of the VMA list but the last few VMAs are
          * not guaranteed to the vma_migratable. If they are not, we would find the
@@ -893,7 +899,7 @@ void task_numa_work(struct callback_head *work)
          * so check it now.
          */
         if (vma)
-                mm->numa_scan_offset = offset;
+                mm->numa_scan_offset = start;
         else
                 reset_ptenuma_scan(p);
         up_read(&mm->mmap_sem);