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Subject[PATCH] mm: thp: fix soft dirty for migration when split
When splitting a huge migrating PMD, we'll transfer the soft dirty bit
from the huge page to the small pages. However we're possibly using a
wrong data since when fetching the bit we're using pmd_soft_dirty()
upon a migration entry. Fix it up.

CC: Andrea Arcangeli <>
CC: Andrew Morton <>
CC: "Kirill A. Shutemov" <>
CC: Matthew Wilcox <>
CC: Michal Hocko <>
CC: Dave Jiang <>
CC: "Aneesh Kumar K.V" <>
CC: Souptick Joarder <>
CC: Konstantin Khlebnikov <>
Signed-off-by: Peter Xu <>

I noticed this during code reading. Only compile tested. I'm sending
a patch directly for review comments since it's relatively
straightforward and not easy to test. Please have a look, thanks.
mm/huge_memory.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f2d19e4fe854..fb0787c3dd3b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2161,7 +2161,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
write = pmd_write(old_pmd);
young = pmd_young(old_pmd);
- soft_dirty = pmd_soft_dirty(old_pmd);
+ if (unlikely(pmd_migration))
+ soft_dirty = pmd_swp_soft_dirty(old_pmd);
+ else
+ soft_dirty = pmd_soft_dirty(old_pmd);

* Withdraw the table only after we mark the pmd entry invalid.
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