Re: [PATCH v2 1/3] arm64: mm: support batch clearing of the young flag for large folios
From: Baolin Wang
Date: Thu Dec 18 2025 - 20:05:56 EST
On 2025/12/18 20:20, Ryan Roberts wrote:
On 18/12/2025 07:15, Baolin Wang wrote:
On 2025/12/17 23:43, Ryan Roberts wrote:
Sorry I'm a bit late to the party...
Never mind. It's not late and comments are always welcome :)
On 11/12/2025 08:16, Baolin Wang wrote:
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.
While we are at it, rename the functions to maintain consistency with other
contpte_*() functions.
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/pgtable.h | 12 ++++-----
arch/arm64/mm/contpte.c | 44 ++++++++++++++++++++++----------
2 files changed, 37 insertions(+), 19 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 0944e296dd4a..e03034683156 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1679,10 +1679,10 @@ 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);
+extern int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *ptep, unsigned int nr);
+extern int contpte_clear_flush_young_ptes(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *ptep, unsigned int nr);
The "contpte_" functions are intended to be private to the arm64 arch and should
be exposed via the generic APIs. But I don't see any generic batched API for
this, so you're only actually able to pass CONT_PTES as nr. Perhaps you're
planning to define "test_and_clear_young_ptes()" and "clear_flush_young_ptes()"
in later patches?
Right. This is a preparation patch, and will be used in patch 2.
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,
@@ -1854,7 +1854,7 @@ 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);
}
#define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
@@ -1866,7 +1866,7 @@ 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);
}
#define wrprotect_ptes wrprotect_ptes
diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
index c0557945939c..19b122441be3 100644
--- a/arch/arm64/mm/contpte.c
+++ b/arch/arm64/mm/contpte.c
@@ -488,8 +488,9 @@ 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
@@ -500,39 +501,56 @@ int contpte_ptep_test_and_clear_young(struct
vm_area_struct *vma,
* having to unfold.
*/
+ unsigned long start = addr;
Personally I wouldn't bother defining start - just reuse addr. You're
incrementing start in the below loop, so it's more appropriate to call it addr
anyway.
OK.
+ unsigned long end = start + nr * PAGE_SIZE;
int young = 0;
int i;
- ptep = contpte_align_down(ptep);
- addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
+ if (pte_cont(__ptep_get(ptep + nr - 1)))
+ end = ALIGN(end, CONT_PTE_SIZE);
- for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE)
- young |= __ptep_test_and_clear_young(vma, addr, ptep);
+ if (pte_cont(__ptep_get(ptep))) {
+ start = ALIGN_DOWN(start, CONT_PTE_SIZE);
+ ptep = contpte_align_down(ptep);
+ }
+
+ nr = (end - start) / PAGE_SIZE;
+ for (i = 0; i < nr; i++, ptep++, start += PAGE_SIZE)
Given you're now defining end, perhaps we don't need nr?
for (; addr != end; ptep++, addr += PAGE_SIZE)
young |= __ptep_test_and_clear_young(vma, addr, ptep);
Yes, good point.
+ young |= __ptep_test_and_clear_young(vma, start, 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 start = addr;
+ unsigned long end = start + nr * PAGE_SIZE;
+
+ if (pte_cont(__ptep_get(ptep + nr - 1)))
+ end = ALIGN(end, CONT_PTE_SIZE);
+
+ if (pte_cont(__ptep_get(ptep)))
+ start = ALIGN_DOWN(start, CONT_PTE_SIZE);
+
We now have this pattern of expanding contpte blocks up and down in 3 places.
Perhaps create a helper?
Sounds reasonable. How about the following helper?
static pte_t *contpte_align_addr_ptep(unsigned long *start, unsigned long *end,
pte_t *ptep, unsigned int nr)
{
unsigned long end_addr = *start + nr * PAGE_SIZE;
if (pte_cont(__ptep_get(ptep + nr - 1)))
I think this is safe but calling it out to check; you're not checking that the
pte is valid, so theoretically you could have a swap-entry here with whatever
overlays the contiguous bit set. So then you would incorrectly extend.
But I think it is safe because the expectation is that core-mm has already
checked that the whole range is present?
Yes. They must be present PTEs that map consecutive pages of the same large folio within a single VMA and a single page table. I will add some comments to make this clear.
*end = ALIGN(end_addr, CONT_PTE_SIZE);
if (pte_cont(__ptep_get(ptep))) {
*start = ALIGN_DOWN(*start, CONT_PTE_SIZE);
ptep = contpte_align_down(ptep);
}
return ptep;
}
Looks good.
Thanks for reviewing.