Re: [PATCH 4/33] mm: add utility functions for ptdesc

On Wed, Apr 19, 2023 at 6:34 AM Vernon Yang <[email protected]> wrote:
>
> On Mon, Apr 17, 2023 at 01:50:19PM -0700, Vishal Moola wrote:
> > Introduce utility functions setting the foundation for ptdescs. These
> > will also assist in the splitting out of ptdesc from struct page.
> >
> > ptdesc_alloc() is defined to allocate new ptdesc pages as compound
> > pages. This is to standardize ptdescs by allowing for one allocation
> > and one free function, in contrast to 2 allocation and 2 free functions.
> >
> > Signed-off-by: Vishal Moola (Oracle) <[email protected]>
> > ---
> >  include/asm-generic/tlb.h | 11 ++++++++++
> >  include/linux/mm.h        | 44 +++++++++++++++++++++++++++++++++++++++
> >  include/linux/pgtable.h   | 13 ++++++++++++
> >  3 files changed, 68 insertions(+)
> >
> > diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
> > index b46617207c93..6bade9e0e799 100644
> > --- a/include/asm-generic/tlb.h
> > +++ b/include/asm-generic/tlb.h
> > @@ -481,6 +481,17 @@ static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
> >       return tlb_remove_page_size(tlb, page, PAGE_SIZE);
> >  }
> >
> > +static inline void tlb_remove_ptdesc(struct mmu_gather *tlb, void *pt)
> > +{
> > +     tlb_remove_table(tlb, pt);
> > +}
> > +
> > +/* Like tlb_remove_ptdesc, but for page-like page directories. */
> > +static inline void tlb_remove_page_ptdesc(struct mmu_gather *tlb, struct ptdesc *pt)
> > +{
> > +     tlb_remove_page(tlb, ptdesc_page(pt));
> > +}
> > +
> >  static inline void tlb_change_page_size(struct mmu_gather *tlb,
> >                                                    unsigned int page_size)
> >  {
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index b18848ae7e22..ec3cbe2fa665 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2744,6 +2744,45 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a
> >  }
> >  #endif /* CONFIG_MMU */
> >
> > +static inline struct ptdesc *virt_to_ptdesc(const void *x)
> > +{
> > +     return page_ptdesc(virt_to_head_page(x));
> > +}
> > +
> > +static inline void *ptdesc_to_virt(struct ptdesc *pt)
> > +{
> > +     return page_to_virt(ptdesc_page(pt));
> > +}
> > +
> > +static inline void *ptdesc_address(struct ptdesc *pt)
> > +{
> > +     return folio_address(ptdesc_folio(pt));
> > +}
> > +
> > +static inline bool ptdesc_is_reserved(struct ptdesc *pt)
> > +{
> > +     return folio_test_reserved(ptdesc_folio(pt));
> > +}
> > +
> > +static inline struct ptdesc *ptdesc_alloc(gfp_t gfp, unsigned int order)
> > +{
> > +     struct page *page = alloc_pages(gfp | __GFP_COMP, order);
> > +
> > +     return page_ptdesc(page);
> > +}
> > +
> > +static inline void ptdesc_free(struct ptdesc *pt)
> > +{
> > +     struct page *page = ptdesc_page(pt);
> > +
> > +     __free_pages(page, compound_order(page));
> > +}
> > +
> > +static inline void ptdesc_clear(void *x)
> > +{
> > +     clear_page(x);
> > +}
> > +
> >  #if USE_SPLIT_PTE_PTLOCKS
> >  #if ALLOC_SPLIT_PTLOCKS
> >  void __init ptlock_cache_init(void);
> > @@ -2970,6 +3009,11 @@ static inline void mark_page_reserved(struct page *page)
> >       adjust_managed_page_count(page, -1);
> >  }
> >
> > +static inline void free_reserved_ptdesc(struct ptdesc *pt)
> > +{
> > +     free_reserved_page(ptdesc_page(pt));
> > +}
> > +
> >  /*
> >   * Default method to free all the __init memory into the buddy system.
> >   * The freed pages will be poisoned with pattern "poison" if it's within
> > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> > index 7cc6ea057ee9..7cd803aa38eb 100644
> > --- a/include/linux/pgtable.h
> > +++ b/include/linux/pgtable.h
> > @@ -97,6 +97,19 @@ TABLE_MATCH(ptl, ptl);
> >  #undef TABLE_MATCH
> >  static_assert(sizeof(struct ptdesc) <= sizeof(struct page));
> >
> > +#define ptdesc_page(pt)                      (_Generic((pt),                 \
> > +     const struct ptdesc *:          (const struct page *)(pt),      \
> > +     struct ptdesc *:                (struct page *)(pt)))
> > +
> > +#define ptdesc_folio(pt)             (_Generic((pt),                 \
> > +     const struct ptdesc *:          (const struct folio *)(pt),     \
> > +     struct ptdesc *:                (struct folio *)(pt)))
> > +
> > +static inline struct ptdesc *page_ptdesc(struct page *page)
> > +{
> > +     return (struct ptdesc *)page;
> > +}
>
> Hi Vishal,
>
> I'm a little curious, why is the page_ptdesc() using inline functions instead of macro?
> If this is any magic, please tell me, thank you very much.

No magic here, I was mainly basing it off Matthew's netmem
series. I'm not too clear on when to use macros vs inlines
myself :/.

If there's a benefit to having it be a macro let me
know and I can make that change in v2.

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