[PATCH v4 4/5] arm64: mm: implement the architecture-specific clear_flush_young_ptes()

[Baolin Wang]

Implement the Arm64 architecture-specific clear_flush_young_ptes() to enable
batched checking of young flags and TLB flushing, improving performance during
large folio reclamation.

Performance testing:
Allocate 10G clean file-backed folios by mmap() in a memory cgroup, and try to
reclaim 8G file-backed folios via the memory.reclaim interface. I can observe
33% performance improvement on my Arm64 32-core server (and 10%+ improvement
on my X86 machine). Meanwhile, the hotspot folio_check_references() dropped
from approximately 35% to around 5%.

W/o patchset:
real	0m1.518s
user	0m0.000s
sys	0m1.518s

W/ patchset:
real	0m1.018s
user	0m0.000s
sys	0m1.018s

Signed-off-by: Baolin Wang <baolin.wang at linux.alibaba.com>
---
 arch/arm64/include/asm/pgtable.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index d5fbe72e820a..84a6bdabb1f9 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1838,6 +1838,17 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
 	return contpte_clear_flush_young_ptes(vma, addr, ptep, CONT_PTES);
 }
 
+#define clear_flush_young_ptes clear_flush_young_ptes
+static inline int clear_flush_young_ptes(struct vm_area_struct *vma,
+					unsigned long addr, pte_t *ptep,
+					unsigned int nr)
+{
+	if (likely(nr == 1 && !pte_cont(__ptep_get(ptep))))
+		return __ptep_clear_flush_young(vma, addr, ptep);
+
+	return contpte_clear_flush_young_ptes(vma, addr, ptep, nr);
+}
+
 #define wrprotect_ptes wrprotect_ptes
 static __always_inline void wrprotect_ptes(struct mm_struct *mm,
 				unsigned long addr, pte_t *ptep, unsigned int nr)
-- 
2.47.3