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

Xavier
2025-04-15T08:30:11Z

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@163.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