linux-kernel - [PATCHv2 3/8] khugepaged: Drain all LRU caches before scanning pages

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Date:   Fri,  3 Apr 2020 14:29:23 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...hat.com>
Cc:     Zi Yan <ziy@...dia.com>, Yang Shi <yang.shi@...ux.alibaba.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv2 3/8] khugepaged: Drain all LRU caches before scanning pages

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@...ux.intel.com>
---
 mm/khugepaged.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 14d7afc90786..fdc10ffde1ca 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2065,6 +2065,8 @@ 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;
-- 
2.26.0