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

Commit Message

Nicholas Piggin Dec. 20, 2020, 4:55 a.m. UTC

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

Signed-off-by: Nicholas Piggin <[e-mail]>
---
 mm/huge_memory.c | 14 ++++++++++----
 mm/hugetlb.c     |  2 +-
 2 files changed, 11 insertions(+), 5 deletions(-)

Patch

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