Re: [PATCH v6 03/33] pgtable: Create struct ptdesc

On Mon, Jun 26, 2023 at 08:14:01PM -0700, Vishal Moola (Oracle) wrote:
> Currently, page table information is stored within struct page. As part
> of simplifying struct page, create struct ptdesc for page table
> information.
> 
> Signed-off-by: Vishal Moola (Oracle) <[email protected]>
> Acked-by: Mike Rapoport (IBM) <[email protected]>
> ---
>  include/linux/pgtable.h | 68 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 68 insertions(+)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 5063b482e34f..d46cb709ce08 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -987,6 +987,74 @@ static inline void ptep_modify_prot_commit(struct vm_area_struct *vma,
>  #endif /* __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION */
>  #endif /* CONFIG_MMU */
>  
> +
> +/**
> + * struct ptdesc -    Memory descriptor for page tables.
> + * @__page_flags:     Same as page flags. Unused for page tables.
> + * @pt_rcu_head:      For freeing page table pages.
> + * @pt_list:          List of used page tables. Used for s390 and x86.
> + * @_pt_pad_1:        Padding that aliases with page's compound head.
> + * @pmd_huge_pte:     Protected by ptdesc->ptl, used for THPs.
> + * @_pt_s390_gaddr:   Aliases with page's mapping. Used for s390 gmap only.

Should some arch-specific bits (and a few others) always under some
#ifdefs, so it shouldn't appear on other archs?

> + * @pt_mm:            Used for x86 pgds.
> + * @pt_frag_refcount: For fragmented page table tracking. Powerpc and s390 only.
> + * @ptl:              Lock for the page table.
> + * @__page_type:      Same as page->page_type. Unused for page tables.
> + * @_refcount:        Same as page refcount. Used for s390 page tables.
> + * @pt_memcg_data:    Memcg data. Tracked for page tables here.
> + *
> + * This struct overlays struct page for now. Do not modify without a good
> + * understanding of the issues.
> + */
> +struct ptdesc {
> +	unsigned long __page_flags;
> +
> +	union {
> +		struct rcu_head pt_rcu_head;
> +		struct list_head pt_list;
> +		struct {
> +			unsigned long _pt_pad_1;
> +			pgtable_t pmd_huge_pte;
> +		};
> +	};
> +	unsigned long _pt_s390_gaddr;
> +
> +	union {
> +		struct mm_struct *pt_mm;
> +		atomic_t pt_frag_refcount;
> +	};
> +
> +	union {
> +		unsigned long _pt_pad_2;
> +#if ALLOC_SPLIT_PTLOCKS
> +		spinlock_t *ptl;
> +#else
> +		spinlock_t ptl;
> +#endif
> +	};
> +	unsigned int __page_type;
> +	atomic_t _refcount;
> +#ifdef CONFIG_MEMCG
> +	unsigned long pt_memcg_data;
> +#endif
> +};

-- 
Peter Xu