[PATCH] mm: mark head page dirty in split_huge_page

[Minchan Kim]

In thp split in old THP refcount, we mappped all of pages
(ie, head + tails) to pte_mkdirty and mark PG_flags to every
tail pages.

But with THP refcount redesign, we can lose dirty bit in page table
and PG_dirty for head page if we want to free the THP page using
migration_entry.

It ends up discarding head page by madvise_free suddenly.
This patch fixes it by mark the head page PG_dirty when VM splits
the THP page.

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 mm/huge_memory.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index adccfb48ce57..7fbbd42554a1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3258,6 +3258,7 @@ static void __split_huge_page(struct page *page, struct list_head *list)
 	atomic_sub(tail_mapcount, &head->_count);
 
 	ClearPageCompound(head);
+	SetPageDirty(head);
 	spin_unlock_irq(&zone->lru_lock);
 
 	unfreeze_page(page_anon_vma(head), head);
-- 
1.9.1

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