[PATCH] HWPOISON: fix wrong num_poisoned_pages in handling memory error on thp

[Naoya Horiguchi]

num_poisoned_pages counts up the number of pages isolated by memory errors.
But for thp, only one subpage is isolated because memory error handler
splits it, so it's wrong to add (1 << compound_trans_order).

Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
---
 mm/memory-failure.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git mmotm-2013-01-23-17-04.orig/mm/memory-failure.c mmotm-2013-01-23-17-04/mm/memory-failure.c
index 9cab165..d5c50d6 100644
--- mmotm-2013-01-23-17-04.orig/mm/memory-failure.c
+++ mmotm-2013-01-23-17-04/mm/memory-failure.c
@@ -1039,7 +1039,14 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 		return 0;
 	}
 
-	nr_pages = 1 << compound_trans_order(hpage);
+	/*
+	 * If a thp is hit by a memory failure, it's supposed to be split.
+	 * So we should add only one to num_poisoned_pages for that case.
+	 */
+	if (PageHuge(p))
+		nr_pages = 1 << compound_trans_order(hpage);
+	else /* normal page or thp */
+		nr_pages = 1;
 	atomic_long_add(nr_pages, &num_poisoned_pages);
 
 	/*
-- 
1.7.11.7

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