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

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Message-Id: <20200416160026.16538-4-kirill.shutemov@linux.intel.com>
Date:   Thu, 16 Apr 2020 19:00:21 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...hat.com>
Cc:     Zi Yan <ziy@...dia.com>, Yang Shi <yang.shi@...ux.alibaba.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        William Kucharski <william.kucharski@...cle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv4 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>
Reviewed-by: William Kucharski <william.kucharski@...cle.com>
Reviewed-and-Tested-by: Zi Yan <ziy@...dia.com>
Acked-by: Yang Shi <yang.shi@...ux.alibaba.com>
---
 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