Messages in this thread Patch in this message | | | Date | Tue, 27 Feb 2024 10:14:43 +0100 | Subject | Re: [PATCH] mm: export folio_pte_batch as a couple of modules might need it | From | David Hildenbrand <> |
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On 27.02.24 10:07, Ryan Roberts wrote: > On 27/02/2024 02:40, Barry Song wrote: >> From: Barry Song <v-songbaohua@oppo.com> >> >> madvise and some others might need folio_pte_batch to check if a range >> of PTEs are completely mapped to a large folio with contiguous physcial >> addresses. Let's export it for others to use. >> >> Cc: Lance Yang <ioworker0@gmail.com> >> Cc: Ryan Roberts <ryan.roberts@arm.com> >> Cc: David Hildenbrand <david@redhat.com> >> Cc: Yin Fengwei <fengwei.yin@intel.com> >> Signed-off-by: Barry Song <v-songbaohua@oppo.com> >> --- >> -v1: >> at least two jobs madv_free and madv_pageout depend on it. To avoid >> conflicts and dependencies, after discussing with Lance, we prefer >> this one can land earlier. > > I think this will also ultimately be useful for mprotect too, though I haven't > looked at it properly yet. >
Yes, I think we briefly discussed that.
>> >> mm/internal.h | 13 +++++++++++++ >> mm/memory.c | 11 +---------- >> 2 files changed, 14 insertions(+), 10 deletions(-) >> >> diff --git a/mm/internal.h b/mm/internal.h >> index 13b59d384845..8e2bc304f671 100644 >> --- a/mm/internal.h >> +++ b/mm/internal.h >> @@ -83,6 +83,19 @@ static inline void *folio_raw_mapping(struct folio *folio) >> return (void *)(mapping & ~PAGE_MAPPING_FLAGS); >> } >> >> +/* Flags for folio_pte_batch(). */ >> +typedef int __bitwise fpb_t; >> + >> +/* Compare PTEs after pte_mkclean(), ignoring the dirty bit. */ >> +#define FPB_IGNORE_DIRTY ((__force fpb_t)BIT(0)) >> + >> +/* Compare PTEs after pte_clear_soft_dirty(), ignoring the soft-dirty bit. */ >> +#define FPB_IGNORE_SOFT_DIRTY ((__force fpb_t)BIT(1)) >> + >> +extern int folio_pte_batch(struct folio *folio, unsigned long addr, >> + pte_t *start_ptep, pte_t pte, int max_nr, fpb_t flags, >> + bool *any_writable); >> + >> void __acct_reclaim_writeback(pg_data_t *pgdat, struct folio *folio, >> int nr_throttled); >> static inline void acct_reclaim_writeback(struct folio *folio) >> diff --git a/mm/memory.c b/mm/memory.c >> index 1c45b6a42a1b..319b3be05e75 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -953,15 +953,6 @@ static __always_inline void __copy_present_ptes(struct vm_area_struct *dst_vma, >> set_ptes(dst_vma->vm_mm, addr, dst_pte, pte, nr); >> } >> >> -/* Flags for folio_pte_batch(). */ >> -typedef int __bitwise fpb_t; >> - >> -/* Compare PTEs after pte_mkclean(), ignoring the dirty bit. */ >> -#define FPB_IGNORE_DIRTY ((__force fpb_t)BIT(0)) >> - >> -/* Compare PTEs after pte_clear_soft_dirty(), ignoring the soft-dirty bit. */ >> -#define FPB_IGNORE_SOFT_DIRTY ((__force fpb_t)BIT(1)) >> - >> static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags) >> { >> if (flags & FPB_IGNORE_DIRTY) >> @@ -982,7 +973,7 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags) >> * If "any_writable" is set, it will indicate if any other PTE besides the >> * first (given) PTE is writable. >> */ > > David was talking in Lance's patch thread, about improving the docs for this > function now that its exported. Might be worth syncing on that.
Here is my take:
Signed-off-by: David Hildenbrand <david@redhat.com> --- mm/memory.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c index d0b855a1837a8..098356b8805ae 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -971,16 +971,28 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags) return pte_wrprotect(pte_mkold(pte)); } -/* +/** + * folio_pte_batch - detect a PTE batch for a large folio + * @folio: The large folio to detect a PTE batch for. + * @addr: The user virtual address the first page is mapped at. + * @start_ptep: Page table pointer for the first entry. + * @pte: Page table entry for the first page. + * @max_nr: The maximum number of table entries to consider. + * @flags: Flags to modify the PTE batch semantics. + * @any_writable: Optional pointer to indicate whether any entry except the + * first one is writable. + * * Detect a PTE batch: consecutive (present) PTEs that map consecutive - * pages of the same folio. + * pages of the same large folio. * * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN, * the accessed bit, writable bit, dirty bit (with FPB_IGNORE_DIRTY) and * soft-dirty bit (with FPB_IGNORE_SOFT_DIRTY). * - * If "any_writable" is set, it will indicate if any other PTE besides the - * first (given) PTE is writable. + * start_ptep must map any page of the folio. max_nr must be at least one and + * must be limited by the caller so scanning cannot exceed a single page table. + * + * Return: the number of table entries in the batch. */ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, pte_t *start_ptep, pte_t pte, int max_nr, fpb_t flags, @@ -996,6 +1008,8 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, *any_writable = false; VM_WARN_ON_FOLIO(!pte_present(pte), folio); + VM_WARN_ON_FOLIO(!folio_test_large(folio) || max_nr < 1, folio); + VM_WARN_ON_FOLIO(page_folio(pfn_to_page(pte_pfn(pte))) != folio, folio); nr = pte_batch_hint(start_ptep, pte); expected_pte = __pte_batch_clear_ignored(pte_advance_pfn(pte, nr), flags); -- 2.43.2
> >> -static inline int folio_pte_batch(struct folio *folio, unsigned long addr, >> +int folio_pte_batch(struct folio *folio, unsigned long addr, > > fork() is very performance sensitive. Is there a risk we are regressing > performance by making this out-of-line? Although its in the same compilation > unit so the compiler may well inline it anyway?
Easy to verify by looking at the generated asm I guess?
> > Either way, perhaps we are better off making it inline in the header? That would > avoid needing to rerun David's micro-benchmarks for fork() and munmap().
That way, the compiler can most certainly better optimize it also outside of mm/memory.c
-- Cheers,
David / dhildenb
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