On 25/12/2025 02:48, Baolin Wang wrote:

On 2025/12/24 22:07, Ryan Roberts wrote:

quoted

On 23/12/2025 05:48, Baolin Wang wrote:

quoted

Currently, contpte_ptep_test_and_clear_young() and
contpte_ptep_clear_flush_young()
only clear the young flag and flush TLBs for PTEs within the contiguous range.
To support batch PTE operations for other sized large folios in the following
patches, adding a new parameter to specify the number of PTEs that map
consecutive
pages of the same large folio in a single VMA and a single page table.

While we are at it, rename the functions to maintain consistency with other
contpte_*() functions.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
  arch/arm64/include/asm/pgtable.h | 12 ++++++------
  arch/arm64/mm/contpte.c          | 33 ++++++++++++++++++--------------
  2 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 445e18e92221..d5fbe72e820a 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h

@@ -1648,10 +1648,10 @@ extern void contpte_clear_full_ptes(struct mm_struct

*mm, unsigned long addr,
  extern pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm,
                  unsigned long addr, pte_t *ptep,
                  unsigned int nr, int full);
-extern int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma,
-                unsigned long addr, pte_t *ptep);
-extern int contpte_ptep_clear_flush_young(struct vm_area_struct *vma,
-                unsigned long addr, pte_t *ptep);
+int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma,
+                unsigned long addr, pte_t *ptep, unsigned int nr);
+int contpte_clear_flush_young_ptes(struct vm_area_struct *vma,
+                unsigned long addr, pte_t *ptep, unsigned int nr);
  extern void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr,
                  pte_t *ptep, unsigned int nr);
  extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma,

@@ -1823,7 +1823,7 @@ static inline int ptep_test_and_clear_young(struct

vm_area_struct *vma,
      if (likely(!pte_valid_cont(orig_pte)))
          return __ptep_test_and_clear_young(vma, addr, ptep);
  -    return contpte_ptep_test_and_clear_young(vma, addr, ptep);
+    return contpte_test_and_clear_young_ptes(vma, addr, ptep, CONT_PTES);

As per your fixup patch, I agree that nr should be 1 here, not CONT_PTES.

Yes.

quoted

quoted

  }
    #define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH

@@ -1835,7 +1835,7 @@ static inline int ptep_clear_flush_young(struct

vm_area_struct *vma,
      if (likely(!pte_valid_cont(orig_pte)))
          return __ptep_clear_flush_young(vma, addr, ptep);
  -    return contpte_ptep_clear_flush_young(vma, addr, ptep);
+    return contpte_clear_flush_young_ptes(vma, addr, ptep, CONT_PTES);

And same here.

quoted

  }
    #define wrprotect_ptes wrprotect_ptes

diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
index e4ddeb46f25d..b929a455103f 100644
--- a/arch/arm64/mm/contpte.c
+++ b/arch/arm64/mm/contpte.c

@@ -508,8 +508,9 @@ pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm,

  }
  EXPORT_SYMBOL_GPL(contpte_get_and_clear_full_ptes);
  -int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma,
-                    unsigned long addr, pte_t *ptep)
+int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma,
+                    unsigned long addr, pte_t *ptep,
+                    unsigned int nr)
  {
      /*
       * ptep_clear_flush_young() technically requires us to clear the access

@@ -518,41 +519,45 @@ int contpte_ptep_test_and_clear_young(struct

vm_area_struct *vma,
       * contig range when the range is covered by a single folio, we can get
       * away with clearing young for the whole contig range here, so we avoid
       * having to unfold.
+     *
+     * The 'nr' means consecutive (present) PTEs that map consecutive pages
+     * of the same large folio in a single VMA and a single page table.
       */
  +    unsigned long end = addr + nr * PAGE_SIZE;
      int young = 0;
-    int i;
  -    ptep = contpte_align_down(ptep);
-    addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
-
-    for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE)
+    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;
  }
-EXPORT_SYMBOL_GPL(contpte_ptep_test_and_clear_young);
+EXPORT_SYMBOL_GPL(contpte_test_and_clear_young_ptes);
  -int contpte_ptep_clear_flush_young(struct vm_area_struct *vma,
-                    unsigned long addr, pte_t *ptep)
+int contpte_clear_flush_young_ptes(struct vm_area_struct *vma,
+                unsigned long addr, pte_t *ptep,
+                unsigned int nr)
  {
      int young;
  -    young = contpte_ptep_test_and_clear_young(vma, addr, ptep);
+    young = contpte_test_and_clear_young_ptes(vma, addr, ptep, nr);
        if (young) {
+        unsigned long end = addr + nr * PAGE_SIZE;
+
+        contpte_align_addr_ptep(&addr, &end, ptep, nr);
          /*
           * See comment in __ptep_clear_flush_young(); same rationale for
           * eliding the trailing DSB applies here.
           */
-        addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
-        __flush_tlb_range_nosync(vma->vm_mm, addr, addr + CONT_PTE_SIZE,
+        __flush_tlb_range_nosync(vma->vm_mm, addr, end,
                       PAGE_SIZE, true, 3);

Hmm... The requirement is that we must flush the _page_ if clearing access for a
pte that does not have the contiguous bit set, or we must flush the _contpte
block_ if clearing access for a pte that does have the contiguous bit set.

With your changes, you may call for a large range that covers multiple contpte
blocks but only has a single pte in a single contpte block for which the access
bit was previously set. But that will cause flushing the TLB for the full range.
Could this cause a performance issue? Yes, no, maybe... I think it's unlikely
but I wouldn't rule it out in some edge case.

I wonder if it's better to track the sub-ranges where access was cleared and
only issue tlbi for those sub-ranges? Probably just keep it simple (the way you
have done it) until/unless we see an actual problem?

Good question. Indeed, as you said, we flush the TLB per folio now, which might
increase the flush range. However, I think this approach is relatively
reasonable for now.

First, the mm-core also tracks the access status per folio, and it's really
unnecessary to add excessive complexity to track the access status of sub-pages
(or sub-ranges). I can already imagine that tracking the access status for each
cont-block range as well as for non-cont pages across the entire large folio
range, which can be too complicated.

Second, __flush_tlb_range_nosync() is a lightweight flush. I quickly ran a
measurement on my machine and found that the overhead of
__flush_tlb_range_nosync() barely changes between nr=16 and nr=256 (both are
around 40 ns).

I'm not concerned about the direct cost of the flush; I agree it should be
lightweight given we elide the trailing DSB. (although there is a possible case
on older HW that doesn't support TLBI-by-range where this will be converted to
multiple TLBI-by-page instructions and that can cause stalls if there are too
many of them).

My concern was the opportunity cost of evicting the entries for all the
non-accessed parts of the folio from the TLB. But of course, I'm talking
nonsense because the architecture does not allow caching non-accessed entries in
the TLB.

So doesn't sound like a problem; I think we can ignore this. Sorry for the noise.

Therefore, I would still prefer to keep the logic here simple.

Agreed.

Thanks,
Ryan