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Subject[PATCH v3 4/7] mm/thp: Carry over dirty bit when thp splits on pmd
Date
Carry over the dirty bit from pmd to pte when a huge pmd splits.  It
shouldn't be a correctness issue since when pmd_dirty() we'll have the page
marked dirty anyway, however having dirty bit carried over helps the next
initial writes of split ptes on some archs like x86.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/huge_memory.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0611b2fd145a..e8e78d1bac5f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2005,7 +2005,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
pgtable_t pgtable;
pmd_t old_pmd, _pmd;
bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false;
- bool anon_exclusive = false;
+ bool anon_exclusive = false, dirty = false;
unsigned long addr;
int i;

@@ -2098,6 +2098,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
SetPageDirty(page);
write = pmd_write(old_pmd);
young = pmd_young(old_pmd);
+ dirty = pmd_dirty(old_pmd);
soft_dirty = pmd_soft_dirty(old_pmd);
uffd_wp = pmd_uffd_wp(old_pmd);

@@ -2161,6 +2162,9 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
entry = pte_wrprotect(entry);
if (!young)
entry = pte_mkold(entry);
+ /* NOTE: this may set soft-dirty too on some archs */
+ if (dirty)
+ entry = pte_mkdirty(entry);
if (soft_dirty)
entry = pte_mksoft_dirty(entry);
if (uffd_wp)
--
2.32.0
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