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Subject[PATCH v16 7/9] mm: Rotate free list so reported pages are moved to the tail of the list
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From: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Rather than walking over the same pages again and again to get to the pages
that have yet to be reported we can save ourselves a significant amount of
time by simply rotating the list so that when we have a full list of
reported pages the head of the list is pointing to the next non-reported
page. Doing this should save us some significant time when processing each
free list.

This doesn't gain us much in the standard case as all of the non-reported
pages should be near the top of the list already. However in the case of
page shuffling this results in a noticeable improvement. Below are the
will-it-scale page_fault1 w/ THP numbers for 16 tasks with and without
this patch.

Without:
tasks processes processes_idle threads threads_idle
16 8093776.25 0.17 5393242.00 38.20

With:
tasks processes processes_idle threads threads_idle
16 8283274.75 0.17 5594261.00 38.15

Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
---
mm/page_reporting.c | 30 ++++++++++++++++++++++--------
1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 1047c6872d4f..6885e74c2367 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -131,17 +131,27 @@ void __page_reporting_notify(void)
if (PageReported(page))
continue;

- /* Attempt to pull page from list */
- if (!__isolate_free_page(page, order))
- break;
+ /* Attempt to pull page from list and place in scatterlist */
+ if (*offset) {
+ if (!__isolate_free_page(page, order)) {
+ next = page;
+ break;
+ }

- /* Add page to scatter list */
- --(*offset);
- sg_set_page(&sgl[*offset], page, page_len, 0);
+ /* Add page to scatter list */
+ --(*offset);
+ sg_set_page(&sgl[*offset], page, page_len, 0);

- /* If scatterlist isn't full grab more pages */
- if (*offset)
continue;
+ }
+
+ /*
+ * Make the first non-processed page in the free list
+ * the new head of the free list before we release the
+ * zone lock.
+ */
+ if (&page->lru != list && !list_is_first(&page->lru, list))
+ list_rotate_to_front(&page->lru, list);

/* release lock before waiting on report processing */
spin_unlock_irq(&zone->lock);
@@ -169,6 +179,10 @@ void __page_reporting_notify(void)
break;
}

+ /* Rotate any leftover pages to the head of the freelist */
+ if (&next->lru != list && !list_is_first(&next->lru, list))
+ list_rotate_to_front(&next->lru, list);
+
spin_unlock_irq(&zone->lock);

return err;
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