Currently, If VM migrates anonymous page, we lose dirty bit of
page table entry. Instead, VM translates dirty bit of page table
as PG_dirty of page flags. It was okay because dirty bit of
page table for anonymous page was no matter to swap out.
Instead, VM took care of PG_dirty.
However, with introducing MADV_FREE, it's important to keep
page table's dirty bit because It could make MADV_FREE handling
logics more straighforward without taking care of PG_dirty.
This patch aims for preparing to remove PG_dirty check for MADV_FREE.
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
mm/migrate.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/migrate.c b/mm/migrate.c
index 236ee25e79d9..add30c3aaaa9 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -151,6 +151,10 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
if (is_write_migration_entry(entry))
pte = maybe_mkwrite(pte, vma);
+ /* MADV_FREE relies on pte_dirty. */
+ if (PageAnon(new))
+ pte = pte_mkdirty(pte);
+
#ifdef CONFIG_HUGETLB_PAGE
if (PageHuge(new)) {
pte = pte_mkhuge(pte);
--
1.9.1
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