[PATCHv4 4/8] khugepaged: Drain LRU add pagevec after swapin

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

__collapse_huge_page_isolate() may fail due to extra pin in the LRU add
pagevec. It's pretty common for swapin case: we swap in pages just to
fail due to the extra pin.

Drain LRU add pagevec on successful swapin.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-and-Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
---
 mm/khugepaged.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 0b75b9821f44..adc686f13447 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -931,6 +931,11 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 	}
 	vmf.pte--;
 	pte_unmap(vmf.pte);
+
+	/* Drain LRU add pagevec to remove extra pin on the swapped in pages */
+	if (swapped_in)
+		lru_add_drain();
+
 	trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
 	return true;
 }
-- 
2.26.1