linux-kernel - [mm/contpte v3 1/1] mm/contpte: Optimize loop to reduce redundant operations

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Message-Id: <20250415082205.2249918-2-xavier_qy@163.com>
Date: Tue, 15 Apr 2025 16:22:05 +0800
From: Xavier <xavier_qy@....com>
To: ryan.roberts@....com,
	dev.jain@....com,
	ioworker0@...il.com,
	21cnbao@...il.com
Cc: akpm@...ux-foundation.org,
	catalin.marinas@....com,
	david@...hat.com,
	gshan@...hat.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	will@...nel.org,
	willy@...radead.org,
	xavier_qy@....com,
	ziy@...dia.com
Subject: [mm/contpte v3 1/1] mm/contpte: Optimize loop to reduce redundant operations

This commit optimizes the contpte_ptep_get function by adding early
 termination logic. It checks if the dirty and young bits of orig_pte
 are already set and skips redundant bit-setting operations during
 the loop. This reduces unnecessary iterations and improves performance.

Signed-off-by: Xavier <xavier_qy@....com>
---
 arch/arm64/mm/contpte.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
index bcac4f55f9c1..0acfee604947 100644
--- a/arch/arm64/mm/contpte.c
+++ b/arch/arm64/mm/contpte.c
@@ -152,6 +152,16 @@ void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr,
 }
 EXPORT_SYMBOL_GPL(__contpte_try_unfold);
 
+/* Note: in order to improve efficiency, using this macro will modify the
+ * passed-in parameters.*/
+#define CHECK_CONTPTE_FLAG(start, ptep, orig_pte, flag) \
+    for (; (start) < CONT_PTES; (start)++, (ptep)++) { \
+		if (pte_##flag(__ptep_get(ptep))) { \
+				orig_pte = pte_mk##flag(orig_pte); \
+				break; \
+		} \
+    }
+
 pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte)
 {
 	/*
@@ -169,11 +179,17 @@ pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte)
 	for (i = 0; i < CONT_PTES; i++, ptep++) {
 		pte = __ptep_get(ptep);
 
-		if (pte_dirty(pte))
+		if (pte_dirty(pte)) {
 			orig_pte = pte_mkdirty(orig_pte);
+			CHECK_CONTPTE_FLAG(i, ptep, orig_pte, young);
+			break;
+		}
 
-		if (pte_young(pte))
+		if (pte_young(pte)) {
 			orig_pte = pte_mkyoung(orig_pte);
+			CHECK_CONTPTE_FLAG(i, ptep, orig_pte, dirty);
+			break;
+		}
 	}
 
 	return orig_pte;
-- 
2.34.1