Re: [PATCH v6 14/18] arm64/mm: Implement new [get_and_]clear_full_ptes() batch APIs

Mark Rutland
2024-02-15T11:29:07Z

On Thu, Feb 15, 2024 at 10:32:01AM +0000, Ryan Roberts wrote:
> Optimize the contpte implementation to fix some of the
> exit/munmap/dontneed performance regression introduced by the initial
> contpte commit. Subsequent patches will solve it entirely.
>
> During exit(), munmap() or madvise(MADV_DONTNEED), mappings must be
> cleared. Previously this was done 1 PTE at a time. But the core-mm
> supports batched clear via the new [get_and_]clear_full_ptes() APIs. So
> let's implement those APIs and for fully covered contpte mappings, we no
> longer need to unfold the contpte. This significantly reduces unfolding
> operations, reducing the number of tlbis that must be issued.
>
> Tested-by: John Hubbard <jhubbard@nvidia.com>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
> arch/arm64/include/asm/pgtable.h | 67 ++++++++++++++++++++++++++++++++
> arch/arm64/mm/contpte.c | 17 ++++++++
> 2 files changed, 84 insertions(+)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 8643227c318b..a8f1a35e3086 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -965,6 +965,37 @@ static inline pte_t __ptep_get_and_clear(struct mm_struct *mm,
> return pte;
> }
>
> +static inline void __clear_full_ptes(struct mm_struct *mm, unsigned long addr,
> + pte_t *ptep, unsigned int nr, int full)
> +{
> + for (;;) {
> + __ptep_get_and_clear(mm, addr, ptep);
> + if (--nr == 0)
> + break;
> + ptep++;
> + addr += PAGE_SIZE;
> + }
> +}
> +
> +static inline pte_t __get_and_clear_full_ptes(struct mm_struct *mm,
> + unsigned long addr, pte_t *ptep,
> + unsigned int nr, int full)
> +{
> + pte_t pte, tmp_pte;
> +
> + pte = __ptep_get_and_clear(mm, addr, ptep);
> + while (--nr) {
> + ptep++;
> + addr += PAGE_SIZE;
> + tmp_pte = __ptep_get_and_clear(mm, addr, ptep);
> + if (pte_dirty(tmp_pte))
> + pte = pte_mkdirty(pte);
> + if (pte_young(tmp_pte))
> + pte = pte_mkyoung(pte);
> + }
> + return pte;
> +}
> +
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> #define __HAVE_ARCH_PMDP_HUGE_GET_AND_CLEAR
> static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm,
> @@ -1160,6 +1191,11 @@ extern pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte);
> extern pte_t contpte_ptep_get_lockless(pte_t *orig_ptep);
> extern void contpte_set_ptes(struct mm_struct *mm, unsigned long addr,
> pte_t *ptep, pte_t pte, unsigned int nr);
> +extern void contpte_clear_full_ptes(struct mm_struct *mm, unsigned long addr,
> + pte_t *ptep, unsigned int nr, int full);
> +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,
> @@ -1253,6 +1289,35 @@ static inline void pte_clear(struct mm_struct *mm,
> __pte_clear(mm, addr, ptep);
> }
>
> +#define clear_full_ptes clear_full_ptes
> +static inline void clear_full_ptes(struct mm_struct *mm, unsigned long addr,
> + pte_t *ptep, unsigned int nr, int full)
> +{
> + if (likely(nr == 1)) {
> + contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep));
> + __clear_full_ptes(mm, addr, ptep, nr, full);
> + } else {
> + contpte_clear_full_ptes(mm, addr, ptep, nr, full);
> + }
> +}
> +
> +#define get_and_clear_full_ptes get_and_clear_full_ptes
> +static inline pte_t get_and_clear_full_ptes(struct mm_struct *mm,
> + unsigned long addr, pte_t *ptep,
> + unsigned int nr, int full)
> +{
> + pte_t pte;
> +
> + if (likely(nr == 1)) {
> + contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep));
> + pte = __get_and_clear_full_ptes(mm, addr, ptep, nr, full);
> + } else {
> + pte = contpte_get_and_clear_full_ptes(mm, addr, ptep, nr, full);
> + }
> +
> + return pte;
> +}
> +
> #define __HAVE_ARCH_PTEP_GET_AND_CLEAR
> static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
> unsigned long addr, pte_t *ptep)
> @@ -1337,6 +1402,8 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma,
> #define set_pte __set_pte
> #define set_ptes __set_ptes
> #define pte_clear __pte_clear
> +#define clear_full_ptes __clear_full_ptes
> +#define get_and_clear_full_ptes __get_and_clear_full_ptes
> #define __HAVE_ARCH_PTEP_GET_AND_CLEAR
> #define ptep_get_and_clear __ptep_get_and_clear
> #define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
> diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
> index bedb58524535..50e0173dc5ee 100644
> --- a/arch/arm64/mm/contpte.c
> +++ b/arch/arm64/mm/contpte.c
> @@ -212,6 +212,23 @@ void contpte_set_ptes(struct mm_struct *mm, unsigned long addr,
> }
> EXPORT_SYMBOL(contpte_set_ptes);
>
> +void contpte_clear_full_ptes(struct mm_struct *mm, unsigned long addr,
> + pte_t *ptep, unsigned int nr, int full)
> +{
> + contpte_try_unfold_partial(mm, addr, ptep, nr);
> + __clear_full_ptes(mm, addr, ptep, nr, full);
> +}
> +EXPORT_SYMBOL(contpte_clear_full_ptes);
> +
> +pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm,
> + unsigned long addr, pte_t *ptep,
> + unsigned int nr, int full)
> +{
> + contpte_try_unfold_partial(mm, addr, ptep, nr);
> + return __get_and_clear_full_ptes(mm, addr, ptep, nr, full);
> +}
> +EXPORT_SYMBOL(contpte_get_and_clear_full_ptes);
> +
> int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma,
> unsigned long addr, pte_t *ptep)
> {
> --
> 2.25.1
>