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Message-ID: <3c4b1711-5a84-4e7a-b54a-d4955d62ec59@arm.com>
Date: Tue, 16 Apr 2024 17:25:38 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Lance Yang <ioworker0@...il.com>, akpm@...ux-foundation.org
Cc: david@...hat.com, 21cnbao@...il.com, mhocko@...e.com,
fengwei.yin@...el.com, zokeefe@...gle.com, shy828301@...il.com,
xiehuan09@...il.com, wangkefeng.wang@...wei.com, songmuchun@...edance.com,
peterx@...hat.com, minchan@...nel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/3] mm/madvise: introduce clear_young_dirty_ptes()
batch helper
On 16/04/2024 04:34, Lance Yang wrote:
> This commit introduces clear_young_dirty_ptes() to replace mkold_ptes().
> By doing so, we can use the same function for both use cases
> (madvise_pageout and madvise_free), and it also provides the flexibility
> to only clear the dirty flag in the future if needed.
>
> Suggested-by: Ryan Roberts <ryan.roberts@....com>
> Signed-off-by: Lance Yang <ioworker0@...il.com>
Reviewed-by: Ryan Roberts <ryan.roberts@....com>
> ---
> include/linux/mm_types.h | 9 +++++
> include/linux/pgtable.h | 74 ++++++++++++++++++++++++----------------
> mm/madvise.c | 3 +-
> 3 files changed, 55 insertions(+), 31 deletions(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index c432add95913..28822cd65d2a 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -1367,6 +1367,15 @@ enum fault_flag {
>
> typedef unsigned int __bitwise zap_flags_t;
>
> +/* Flags for clear_young_dirty_ptes(). */
> +typedef int __bitwise cydp_t;
> +
> +/* Clear the access bit */
> +#define CYDP_CLEAR_YOUNG ((__force cydp_t)BIT(0))
> +
> +/* Clear the dirty bit */
> +#define CYDP_CLEAR_DIRTY ((__force cydp_t)BIT(1))
> +
> /*
> * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each
> * other. Here is what they mean, and how to use them:
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index e2f45e22a6d1..18019f037bae 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -361,36 +361,6 @@ static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
> }
> #endif
>
> -#ifndef mkold_ptes
> -/**
> - * mkold_ptes - Mark PTEs that map consecutive pages of the same folio as old.
> - * @vma: VMA the pages are mapped into.
> - * @addr: Address the first page is mapped at.
> - * @ptep: Page table pointer for the first entry.
> - * @nr: Number of entries to mark old.
> - *
> - * May be overridden by the architecture; otherwise, implemented as a simple
> - * loop over ptep_test_and_clear_young().
> - *
> - * Note that PTE bits in the PTE range besides the PFN can differ. For example,
> - * some PTEs might be write-protected.
> - *
> - * Context: The caller holds the page table lock. The PTEs map consecutive
> - * pages that belong to the same folio. The PTEs are all in the same PMD.
> - */
> -static inline void mkold_ptes(struct vm_area_struct *vma, unsigned long addr,
> - pte_t *ptep, unsigned int nr)
> -{
> - for (;;) {
> - ptep_test_and_clear_young(vma, addr, ptep);
> - if (--nr == 0)
> - break;
> - ptep++;
> - addr += PAGE_SIZE;
> - }
> -}
> -#endif
> -
> #ifndef __HAVE_ARCH_PMDP_TEST_AND_CLEAR_YOUNG
> #if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)
> static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma,
> @@ -489,6 +459,50 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
> }
> #endif
>
> +#ifndef clear_young_dirty_ptes
> +/**
> + * clear_young_dirty_ptes - Mark PTEs that map consecutive pages of the
> + * same folio as old/clean.
> + * @mm: Address space the pages are mapped into.
> + * @addr: Address the first page is mapped at.
> + * @ptep: Page table pointer for the first entry.
> + * @nr: Number of entries to mark old/clean.
> + * @flags: Flags to modify the PTE batch semantics.
> + *
> + * May be overridden by the architecture; otherwise, implemented by
> + * get_and_clear/modify/set for each pte in the range.
> + *
> + * Note that PTE bits in the PTE range besides the PFN can differ. For example,
> + * some PTEs might be write-protected.
> + *
> + * Context: The caller holds the page table lock. The PTEs map consecutive
> + * pages that belong to the same folio. The PTEs are all in the same PMD.
> + */
> +static inline void clear_young_dirty_ptes(struct vm_area_struct *vma,
> + unsigned long addr, pte_t *ptep,
> + unsigned int nr, cydp_t flags)
> +{
> + pte_t pte;
> +
> + for (;;) {
> + if (flags == CYDP_CLEAR_YOUNG)
> + ptep_test_and_clear_young(vma, addr, ptep);
> + else {
> + pte = ptep_get_and_clear(vma->vm_mm, addr, ptep);
> + if (flags & CYDP_CLEAR_YOUNG)
> + pte = pte_mkold(pte);
> + if (flags & CYDP_CLEAR_DIRTY)
> + pte = pte_mkclean(pte);
> + set_pte_at(vma->vm_mm, addr, ptep, pte);
> + }
> + if (--nr == 0)
> + break;
> + ptep++;
> + addr += PAGE_SIZE;
> + }
> +}
> +#endif
> +
> static inline void ptep_clear(struct mm_struct *mm, unsigned long addr,
> pte_t *ptep)
> {
> diff --git a/mm/madvise.c b/mm/madvise.c
> index f59169888b8e..edb592adb749 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -507,7 +507,8 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> continue;
>
> if (!pageout && pte_young(ptent)) {
> - mkold_ptes(vma, addr, pte, nr);
> + clear_young_dirty_ptes(vma, addr, pte, nr,
> + CYDP_CLEAR_YOUNG);
> tlb_remove_tlb_entries(tlb, pte, nr, addr);
> }
>
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