[PATCH v2 1/1] mm/contpte: Optimize loop to reduce redundant operations

Xavier
2025-04-08T09:15:04Z

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 | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
index bcac4f55f9c1..034d153d7d19 100644
--- a/arch/arm64/mm/contpte.c
+++ b/arch/arm64/mm/contpte.c
@@ -152,6 +152,18 @@ void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr,
}
EXPORT_SYMBOL_GPL(__contpte_try_unfold);

+#define CHECK_CONTPTE_FLAG(start, ptep, orig_pte, flag) \
+ do { \
+ int _start = start; \
+ pte_t *_ptep = ptep; \
+ while (_start++ < CONT_PTES) { \
+ if (pte_##flag(__ptep_get(_ptep++))) { \
+ orig_pte = pte_mk##flag(orig_pte); \
+ break; \
+ } \
+ } \
+ } while (0)
+
pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte)
{
/*
@@ -169,11 +181,17 @@ 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