[PATCH v3 1/3] mm/cow: don't bother write protecting already write-protected huge pages

Nicholas Piggin
2020-12-20T04:55:47Z

This is the HugePage / THP equivalent for 1b2de5d039c8 ("mm/cow: don't
bother write protecting already write-protected pages").

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
mm/huge_memory.c | 14 ++++++++++----
mm/hugetlb.c | 2 +-
2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9237976abe72..87da60c583a9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1111,8 +1111,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
mm_inc_nr_ptes(dst_mm);
pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);

- pmdp_set_wrprotect(src_mm, addr, src_pmd);
- pmd = pmd_mkold(pmd_wrprotect(pmd));
+ if (pmd_write(pmd)) {
+ pmdp_set_wrprotect(src_mm, addr, src_pmd);
+ pmd = pmd_wrprotect(pmd);
+ }
+ pmd = pmd_mkold(pmd);
set_pmd_at(dst_mm, addr, dst_pmd, pmd);

ret = 0;
@@ -1218,8 +1221,11 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
return -EAGAIN;
}

- pudp_set_wrprotect(src_mm, addr, src_pud);
- pud = pud_mkold(pud_wrprotect(pud));
+ if (pud_write(pud)) {
+ pudp_set_wrprotect(src_mm, addr, src_pud);
+ pud = pud_mkold(pud_wrprotect(pud));
+ }
+ pud = pud_mkold(pud);
set_pud_at(dst_mm, addr, dst_pud, pud);

ret = 0;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index cbf32d2824fd..c068ae4b2fef 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3813,7 +3813,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
}
set_huge_swap_pte_at(dst, addr, dst_pte, entry, sz);
} else {
- if (cow) {
+ if (cow && huge_pte_write(entry)) {
/*
* No need to notify as we are downgrading page
* table protection not changing it to point
--
2.23.0