Re: [PATCHv2 4/8] khugepaged: Drain LRU add pagevec after swapin

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On 4/3/20 4:29 AM, Kirill A. Shutemov wrote:
__collapse_huge_page_isolate() may fail due to extra pin in the LRU add
pagevec. It's petty common for swapin case: we swap in pages just to
fail due to the extra pin.

Drain LRU add pagevec on sucessfull swapin.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
  mm/khugepaged.c | 5 +++++
  1 file changed, 5 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index fdc10ffde1ca..57ff287caf6b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -940,6 +940,11 @@ 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();

There is already lru_add_drain() called in swap readahead path, please see swap_vma_readahead() and swap_cluster_readahead().

The extra call to draining lru seems unnecessary.

+
  	trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
  	return true;
  }





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