On 3/6/26 10:47 PM, David Hildenbrand (Arm) wrote:

On 3/6/26 07:43, Baolin Wang wrote:

quoted

Implement the Arm64 architecture-specific test_and_clear_young_ptes() to enable
batched checking of young flags, improving performance during large folio
reclamation when MGLRU is enabled.

While we're at it, simplify ptep_test_and_clear_young() by calling
test_and_clear_young_ptes(). Since callers guarantee that PTEs are present
before calling these functions, we can use pte_cont() to check the CONT_PTE
flag instead of pte_valid_cont().

Performance testing:
Enable MGLRU, then 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 60%+ performance improvement on my Arm64 32-core server (and about
15% improvement on my X86 machine).

W/o patchset:
real	0m0.470s
user	0m0.000s
sys	0m0.470s

W/ patchset:
real	0m0.180s
user	0m0.001s
sys	0m0.179s

Reviewed-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
  arch/arm64/include/asm/pgtable.h | 18 ++++++++++++------
  1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index aa4b13da6371..ab451d20e4c5 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h

@@ -1812,16 +1812,22 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
  	return __ptep_get_and_clear(mm, addr, ptep);
  }
  
+#define test_and_clear_young_ptes test_and_clear_young_ptes
+static inline int test_and_clear_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_test_and_clear_young(vma, addr, ptep);
+
+	return contpte_test_and_clear_young_ptes(vma, addr, ptep, nr);
+}

Thinking out loud, what would happen if

Good questions, I think the contpte_test_and_clear_young_ptes() takes 
that into account.

(a) The range spans multiple possible cont ranges (like, 64 ptes).

The contpte_test_and_clear_young_ptes() will call 
contpte_align_addr_ptep() to align the range to cont‑block boundary, 
that means the range can span multiple cont blocks.

int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma,
					unsigned long addr, pte_t *ptep,
					unsigned int nr)
{
	unsigned long end = addr + nr * PAGE_SIZE;
	int young = 0;

	ptep = contpte_align_addr_ptep(&addr, &end, ptep, nr);
	for (; addr != end; ptep++, addr += PAGE_SIZE)
		young |= __ptep_test_and_clear_young(vma, addr, ptep);

	return young;
}

(b) The first pte is !pte_cont(), but some others in there are?

IMO they can’t be handled in a single batch. Since the folio_pte_batch() 
will group consecutive !cont PTEs into one batch and consecutive cont 
PTEs into another (assume all PTEs belong to a single large folio), 
because their PTE entries have different CONT bits.

Even if the callers do so, contpte_align_addr_ptep() will check the 
pte_cont() of the start and end address to align the range appropriately.