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@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Link: http://lkml.kernel.org/r/20200416160026.16538-4-kirill.shutemov@linux.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index c436fd3..8a74b97 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2079,6 +2079,8 @@ 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;