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> - page_is_fake_head(): no longer needed; > - page_count_writable(): no longer needed for RCU protection; > - RCU read_lock in page_ref_add_unless(): no longer needed; > > This substantially simplifies compound_head() and page_ref_add_unless()= , > removing both branches and RCU overhead from these hot paths. > > Signed-off-by: Kiryl Shutsemau > Reviewed-by: Muchun Song > --- > include/linux/page-flags.h | 93 ++------------------------------------= > include/linux/page_ref.h | 8 +--- > 2 files changed, 4 insertions(+), 97 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index e16a4bc82856..660f9154a211 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -221,102 +221,15 @@ static __always_inline bool compound_info_has_ma= sk(void) > return is_power_of_2(sizeof(struct page)); > } > > -#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP > DECLARE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key); > > -/* > - * Return the real head page struct iff the @page is a fake head page,= otherwise > - * return the @page itself. See Documentation/mm/vmemmap_dedup.rst. > - */ > -static __always_inline const struct page *page_fixed_fake_head(const s= truct page *page) > -{ > - if (!static_branch_unlikely(&hugetlb_optimize_vmemmap_key)) > - return page; > - > - /* Fake heads only exists if compound_info_has_mask() is true */ > - if (!compound_info_has_mask()) > - return page; > - > - /* > - * Only addresses aligned with PAGE_SIZE of struct page may be fake h= ead > - * struct page. The alignment check aims to avoid access the fields (= > - * e.g. compound_info) of the @page[1]. It can avoid touch a (possibl= y) > - * cold cacheline in some cases. > - */ > - if (IS_ALIGNED((unsigned long)page, PAGE_SIZE) && > - test_bit(PG_head, &page->flags.f)) { > - /* > - * We can safely access the field of the @page[1] with PG_head > - * because the @page is a compound page composed with at least > - * two contiguous pages. > - */ > - unsigned long info =3D READ_ONCE(page[1].compound_info); > - > - /* See set_compound_head() */ > - if (likely(info & 1)) { > - unsigned long p =3D (unsigned long)page; > - > - return (const struct page *)(p & info); > - } > - } > - return page; > -} > - > static __always_inline unsigned long _compound_head(const struct page = *page) > { > unsigned long info =3D READ_ONCE(page->compound_info); > > /* Bit 0 encodes PageTail() */ > if (!(info & 1)) > - return (unsigned long)page_fixed_fake_head(page); > + return (unsigned long)page; Is this right? Assuming 64B struct page and 4KB page size, thus 64 struct= pages in a page, the 64th struct page (0-indexed) is mapped to the head page an= d has !(info & 1). But _compound_head() should return page & info here. Am I missing something? Thanks. Best Regards, Yan, Zi