Messages in this thread | | | Date | Tue, 5 Dec 2023 14:17:38 +0100 | Subject | Re: [PATCH RFC 34/39] mm/rmap: introduce folio_try_dup_anon_rmap_[pte|ptes|pmd]() | From | David Hildenbrand <> |
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On 05.12.23 14:12, Ryan Roberts wrote: > On 04/12/2023 14:21, David Hildenbrand wrote: >> The last user of page_needs_cow_for_dma() and __page_dup_rmap() are gone, >> remove them. >> >> Add folio_try_dup_anon_rmap_ptes() right away, we want to perform rmap >> baching during fork() soon. >> >> Signed-off-by: David Hildenbrand <david@redhat.com> >> --- >> include/linux/mm.h | 6 -- >> include/linux/rmap.h | 145 +++++++++++++++++++++++++++++-------------- >> 2 files changed, 100 insertions(+), 51 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 24c1c7c5a99c0..f7565b35ae931 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -1964,12 +1964,6 @@ static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma, >> return folio_maybe_dma_pinned(folio); >> } >> >> -static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma, >> - struct page *page) >> -{ >> - return folio_needs_cow_for_dma(vma, page_folio(page)); >> -} >> - >> /** >> * is_zero_page - Query if a page is a zero page >> * @page: The page to query >> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >> index 21d72cc602adc..84439f7720c62 100644 >> --- a/include/linux/rmap.h >> +++ b/include/linux/rmap.h >> @@ -354,68 +354,123 @@ static inline void folio_dup_file_rmap_pmd(struct folio *folio, >> #endif >> } >> >> -static inline void __page_dup_rmap(struct page *page, bool compound) >> +static inline int __folio_try_dup_anon_rmap(struct folio *folio, > > __always_inline?
Yes.
> >> + struct page *page, unsigned int nr_pages, >> + struct vm_area_struct *src_vma, enum rmap_mode mode) >> { >> - VM_WARN_ON(folio_test_hugetlb(page_folio(page))); >> + int i; >> >> - if (compound) { >> - struct folio *folio = (struct folio *)page; >> + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); >> >> - VM_BUG_ON_PAGE(compound && !PageHead(page), page); >> - atomic_inc(&folio->_entire_mapcount); >> - } else { >> - atomic_inc(&page->_mapcount); >> + /* >> + * No need to check+clear for already shared PTEs/PMDs of the folio. >> + * This includes PTE mappings of (order-0) KSM folios. >> + */ >> + if (likely(mode == RMAP_MODE_PTE)) { > > Presumbly if __always_inline then the compiler will remove this if/else and just > keep the part indicated by mode? In which case "likely" is pretty useless? Same > for all similar sites in the other patches.
Yes, also had this in mind. As long as we use __always_inline it shouldn't ever matter.
> >> + for (i = 0; i < nr_pages; i++) { >> + if (PageAnonExclusive(page + i)) >> + goto clear; >> + } >> + } else if (mode == RMAP_MODE_PMD) { >> + if (PageAnonExclusive(page)) >> + goto clear; >> } >> + goto dup; >> + >> +clear: >> + /* >> + * If this folio may have been pinned by the parent process, >> + * don't allow to duplicate the mappings but instead require to e.g., >> + * copy the subpage immediately for the child so that we'll always >> + * guarantee the pinned folio won't be randomly replaced in the >> + * future on write faults. >> + */ >> + if (likely(!folio_is_device_private(folio) && >> + unlikely(folio_needs_cow_for_dma(src_vma, folio)))) >> + return -EBUSY; >> + >> + if (likely(mode == RMAP_MODE_PTE)) { >> + for (i = 0; i < nr_pages; i++) > > Do you really need to reset i=0 here? You have already checked that lower pages > are shared in the above loop, so can't you just start from the first exclusive > page here?
It's best to check the updated patch I sent.
-- Cheers,
David / dhildenb
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