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Date:   Thu, 8 Jun 2023 18:20:04 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
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        Mike Rapoport <rppt@kernel.org>,
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        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH v2 11/32] mm/vmwgfx: simplify pmd & pud mapping dirty
 helpers
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wp_clean_pmd_entry() need not check pmd_trans_unstable() or pmd_none(),
wp_clean_pud_entry() need not check pud_trans_unstable() or pud_none():
it's just the ACTION_CONTINUE when trans_huge or devmap that's needed
to prevent splitting, and we're hoping to remove pmd_trans_unstable().
Is that PUD #ifdef necessary?  Maybe some configs are missing a stub.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
 mm/mapping_dirty_helpers.c | 34 +++++++++-------------------------
 1 file changed, 9 insertions(+), 25 deletions(-)

diff --git a/mm/mapping_dirty_helpers.c b/mm/mapping_dirty_helpers.c
index e1eb33f49059..87b4beeda4fa 100644
--- a/mm/mapping_dirty_helpers.c
+++ b/mm/mapping_dirty_helpers.c
@@ -128,19 +128,11 @@ static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
 {
 	pmd_t pmdval = pmdp_get_lockless(pmd);
 
-	if (!pmd_trans_unstable(&pmdval))
-		return 0;
-
-	if (pmd_none(pmdval)) {
-		walk->action = ACTION_AGAIN;
-		return 0;
-	}
-
-	/* Huge pmd, present or migrated */
-	walk->action = ACTION_CONTINUE;
-	if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
+	/* Do not split a huge pmd, present or migrated */
+	if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval)) {
 		WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));
-
+		walk->action = ACTION_CONTINUE;
+	}
 	return 0;
 }
 
@@ -156,23 +148,15 @@ static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
 static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
 			      struct mm_walk *walk)
 {
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 	pud_t pudval = READ_ONCE(*pud);
 
-	if (!pud_trans_unstable(&pudval))
-		return 0;
-
-	if (pud_none(pudval)) {
-		walk->action = ACTION_AGAIN;
-		return 0;
-	}
-
-#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
-	/* Huge pud */
-	walk->action = ACTION_CONTINUE;
-	if (pud_trans_huge(pudval) || pud_devmap(pudval))
+	/* Do not split a huge pud */
+	if (pud_trans_huge(pudval) || pud_devmap(pudval)) {
 		WARN_ON(pud_write(pudval) || pud_dirty(pudval));
+		walk->action = ACTION_CONTINUE;
+	}
 #endif
-
 	return 0;
 }
 
-- 
2.35.3