Messages in this thread | | | Date | Tue, 16 Apr 2024 17:01:32 +0200 | Subject | Re: [PATCH v7 1/3] mm/madvise: introduce clear_young_dirty_ptes() batch helper | From | David Hildenbrand <> |
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On 16.04.24 05:34, 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@arm.com> > Signed-off-by: Lance Yang <ioworker0@gmail.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; > + } > +}
The complier *might* generate a bit faster code if you check for CYDP_CLEAR_YOUNG outside of the loop, so you don't have to recheck on each loop iteration.
For now, nothing to lose sleep about
Acked-by: David Hildenbrand <david@redhat.com>
-- Cheers,
David / dhildenb
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