[PATCH v4 2/4] mm: mprotect: avoid unnecessary struct page accessing if pte_protnone()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

If the pte_protnone() is true, we could avoid unnecessary struct page
accessing and reduce cache footprint when scanning page tables for prot
numa, there was a similar change before, see more commit a818f5363a0e
("autonuma: reduce cache footprint when scanning page tables").

Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 mm/mprotect.c | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 056986d9076a..6236d120c8e6 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -118,18 +118,13 @@ static int mprotect_folio_pte_batch(struct folio *folio, pte_t *ptep,
 	return folio_pte_batch_flags(folio, NULL, ptep, &pte, max_nr_ptes, flags);
 }
 
-static bool prot_numa_skip(struct vm_area_struct *vma, unsigned long addr,
-			   pte_t oldpte, pte_t *pte, int target_node,
-			   struct folio *folio)
+static bool prot_numa_skip(struct vm_area_struct *vma, int target_node,
+		struct folio *folio)
 {
 	bool ret = true;
 	bool toptier;
 	int nid;
 
-	/* Avoid TLB flush if possible */
-	if (pte_protnone(oldpte))
-		goto skip;
-
 	if (!folio)
 		goto skip;
 
@@ -307,23 +302,25 @@ static long change_pte_range(struct mmu_gather *tlb,
 			struct page *page;
 			pte_t ptent;
 
+			/* Already in the desired state. */
+			if (prot_numa && pte_protnone(oldpte))
+				continue;
+
 			page = vm_normal_page(vma, addr, oldpte);
 			if (page)
 				folio = page_folio(page);
+
 			/*
 			 * Avoid trapping faults against the zero or KSM
 			 * pages. See similar comment in change_huge_pmd.
 			 */
-			if (prot_numa) {
-				int ret = prot_numa_skip(vma, addr, oldpte, pte,
-							 target_node, folio);
-				if (ret) {
+			if (prot_numa &&
+			    prot_numa_skip(vma, target_node, folio)) {
 
-					/* determine batch to skip */
-					nr_ptes = mprotect_folio_pte_batch(folio,
-						  pte, oldpte, max_nr_ptes, /* flags = */ 0);
-					continue;
-				}
+				/* determine batch to skip */
+				nr_ptes = mprotect_folio_pte_batch(folio,
+					  pte, oldpte, max_nr_ptes, /* flags = */ 0);
+				continue;
 			}
 
 			nr_ptes = mprotect_folio_pte_batch(folio, pte, oldpte, max_nr_ptes, flags);
-- 
2.27.0