[PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the tail of the list

[Alexander Duyck <alexander.duyck@xxxxxxxxx>]

From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx>
---
 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;