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

[Vernon Yang <vernon2gm@xxxxxxxxx>]

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) <vishal.moola@xxxxxxxxx>
> ---
>  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.

> +
>  /*
>   * A page table page can be thought of an array like this: 
> pXd_t[PTRS_PER_PxD]
>   *
>
> --
> 2.39.2
>