Re: [PATCH v2 05/34] mm: add utility functions for ptdesc

On Mon, May 01, 2023 at 12:28:00PM -0700, Vishal Moola (Oracle) 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   | 12 +++++++++++
>  3 files changed, 67 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..258f3b730359 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));

Do we ever use compound pages for page tables?

> +}
> +
> +static inline void *ptdesc_to_virt(const struct ptdesc *pt)
> +{
> +	return page_to_virt(ptdesc_page(pt));
> +}
> +
> +static inline void *ptdesc_address(const 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));
> +}

The ptdesc_{alloc,free} API does not sound right to me. The name
ptdesc_alloc() implies the allocation of the ptdesc itself, rather than
allocation of page table page. The same goes for free.

> +
> +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 5e0f51308724..b067ac10f3dd 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1041,6 +1041,18 @@ 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)))
> +
> +#define page_ptdesc(p)			(_Generic((p),			\
> +	const struct page *:		(const struct ptdesc *)(p),	\
> +	struct page *:			(struct ptdesc *)(p)))
> +
>  /*
>   * No-op macros that just return the current protection value. Defined here
>   * because these macros can be used even if CONFIG_MMU is not defined.
> -- 
> 2.39.2
> 
> 

-- 
Sincerely yours,
Mike.