From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Date: Mon, 6 Apr 2020 20:05:10 -0700
Subject: mm/page_reporting: rotate reported pages to the tail of the list
Git-commit: 02cf8719b8cb2b474b37bcbeee4706950b3d1d3d
Patch-mainline: v5.7-rc1
References: MM Functionality, jsc#SLE-12717

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Nitesh Narayan Lal <nitesh@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pankaj Gupta <pagupta@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Wang <wei.w.wang@intel.com>
Cc: Yang Zhang <yang.zhang.wz@gmail.com>
Cc: wei qi <weiqi4@huawei.com>
Link: http://lkml.kernel.org/r/20200211224708.29318.16862.stgit@localhost.localdomain
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/page_reporting.c |   32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -131,17 +131,27 @@ page_reporting_cycle(struct page_reporti
 		if (PageReported(page))
 			continue;
 
-		/* Attempt to pull page from list */
-		if (!__isolate_free_page(page, order))
-			break;
-
-		/* Add page to scatter list */
-		--(*offset);
-		sg_set_page(&sgl[*offset], page, page_len, 0);
+		/* 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);
 
-		/* 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 @@ page_reporting_cycle(struct page_reporti
 			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;