linux-kernel - [PATCH v2 1/7] mm: Refactor code in mprotect

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Message-Id: <20250429052336.18912-2-dev.jain@arm.com>
Date: Tue, 29 Apr 2025 10:53:30 +0530
From: Dev Jain <dev.jain@....com>
To: akpm@...ux-foundation.org
Cc: ryan.roberts@....com,
	david@...hat.com,
	willy@...radead.org,
	linux-mm@...ck.org,
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	Dev Jain <dev.jain@....com>
Subject: [PATCH v2 1/7] mm: Refactor code in mprotect

Reduce indentation in change_pte_range() by refactoring some of the code
into a new function. No functional change.

Signed-off-by: Dev Jain <dev.jain@....com>
---
 mm/mprotect.c | 116 +++++++++++++++++++++++++++++---------------------
 1 file changed, 68 insertions(+), 48 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 88608d0dc2c2..70f59aa8c2a8 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -83,6 +83,71 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr,
 	return pte_dirty(pte);
 }
 
+
+
+static bool prot_numa_skip(struct vm_area_struct *vma, struct folio *folio,
+		int target_node)
+{
+	bool toptier;
+	int nid;
+
+	/* Also skip shared copy-on-write pages */
+	if (is_cow_mapping(vma->vm_flags) &&
+	    (folio_maybe_dma_pinned(folio) ||
+	     folio_maybe_mapped_shared(folio)))
+		return true;
+
+	/*
+	 * While migration can move some dirty pages,
+	 * it cannot move them all from MIGRATE_ASYNC
+	 * context.
+	 */
+	if (folio_is_file_lru(folio) &&
+	    folio_test_dirty(folio))
+		return true;
+
+	/*
+	 * Don't mess with PTEs if page is already on the node
+	 * a single-threaded process is running on.
+	 */
+	nid = folio_nid(folio);
+	if (target_node == nid)
+		return true;
+	toptier = node_is_toptier(nid);
+
+	/*
+	 * Skip scanning top tier node if normal numa
+	 * balancing is disabled
+	 */
+	if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
+	    toptier)
+		return true;
+	return false;
+}
+
+static bool prot_numa_avoid_fault(struct vm_area_struct *vma,
+		unsigned long addr, pte_t oldpte, int target_node)
+{
+	struct folio *folio;
+	int ret;
+
+	/* Avoid TLB flush if possible */
+	if (pte_protnone(oldpte))
+		return true;
+
+	folio = vm_normal_folio(vma, addr, oldpte);
+	if (!folio || folio_is_zone_device(folio) ||
+	    folio_test_ksm(folio))
+		return true;
+	ret = prot_numa_skip(vma, folio, target_node);
+	if (ret)
+		return ret;
+	if (folio_use_access_time(folio))
+		folio_xchg_access_time(folio,
+			jiffies_to_msecs(jiffies));
+	return false;
+}
+
 static long change_pte_range(struct mmu_gather *tlb,
 		struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr,
 		unsigned long end, pgprot_t newprot, unsigned long cp_flags)
@@ -116,56 +181,11 @@ static long change_pte_range(struct mmu_gather *tlb,
 			 * Avoid trapping faults against the zero or KSM
 			 * pages. See similar comment in change_huge_pmd.
 			 */
-			if (prot_numa) {
-				struct folio *folio;
-				int nid;
-				bool toptier;
-
-				/* Avoid TLB flush if possible */
-				if (pte_protnone(oldpte))
-					continue;
-
-				folio = vm_normal_folio(vma, addr, oldpte);
-				if (!folio || folio_is_zone_device(folio) ||
-				    folio_test_ksm(folio))
-					continue;
-
-				/* Also skip shared copy-on-write pages */
-				if (is_cow_mapping(vma->vm_flags) &&
-				    (folio_maybe_dma_pinned(folio) ||
-				     folio_maybe_mapped_shared(folio)))
-					continue;
-
-				/*
-				 * While migration can move some dirty pages,
-				 * it cannot move them all from MIGRATE_ASYNC
-				 * context.
-				 */
-				if (folio_is_file_lru(folio) &&
-				    folio_test_dirty(folio))
+			if (prot_numa &&
+			    prot_numa_avoid_fault(vma, addr,
+						  oldpte, target_node))
 					continue;
 
-				/*
-				 * Don't mess with PTEs if page is already on the node
-				 * a single-threaded process is running on.
-				 */
-				nid = folio_nid(folio);
-				if (target_node == nid)
-					continue;
-				toptier = node_is_toptier(nid);
-
-				/*
-				 * Skip scanning top tier node if normal numa
-				 * balancing is disabled
-				 */
-				if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
-				    toptier)
-					continue;
-				if (folio_use_access_time(folio))
-					folio_xchg_access_time(folio,
-						jiffies_to_msecs(jiffies));
-			}
-
 			oldpte = ptep_modify_prot_start(vma, addr, pte);
 			ptent = pte_modify(oldpte, newprot);
 
-- 
2.30.2