[PATCHv4 3/8] khugepaged: Drain all LRU caches before scanning pages

[Kirill A. Shutemov]

Having a page in LRU add cache offsets page refcount and gives
false-negative on PageLRU(). It reduces collapse success rate.

Drain all LRU add caches before scanning. It happens relatively
rare and should not disturb the system too much.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
Reviewed-and-Tested-by: Zi Yan <ziy@xxxxxxxxxx>
Acked-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
---
 mm/khugepaged.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 6e69dc9a9fb1..0b75b9821f44 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2078,6 +2078,8 @@ static void khugepaged_do_scan(void)
 
 	barrier(); /* write khugepaged_pages_to_scan to local stack */
 
+	lru_add_drain_all();
+
 	while (progress < pages) {
 		if (!khugepaged_prealloc_page(&hpage, &wait))
 			break;
-- 
2.26.1