[PATCHv3, RESEND 3/8] khugepaged: Drain all LRU caches before scanning pages

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: akpm@linux-foundation.org, Andrea Arcangeli <aarcange@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>, Yang Shi <yang.shi@linux.alibaba.com>,
	Ralph Campbell <rcampbell@nvidia.com>,
	John Hubbard <jhubbard@nvidia.com>,
	William Kucharski <william.kucharski@oracle.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCHv3, RESEND 3/8] khugepaged: Drain all LRU caches before scanning pages
Date: Mon, 13 Apr 2020 15:52:15 +0300	[thread overview]
Message-ID: <20200413125220.663-4-kirill.shutemov@linux.intel.com> (raw)
In-Reply-To: <20200413125220.663-1-kirill.shutemov@linux.intel.com>

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

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 5968ec5ddd6b..ee66c140c2d6 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2059,6 +2059,8 @@ 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


