Re: [PATCH 1/7] mm: Document x86 uses a linked list of pgds

[Ira Weiny]

On Tue, Apr 28, 2020 at 12:44:43PM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> 
> x86 uses page->lru of the pages used for pgds, but that's not immediately
> obvious to anyone looking to make changes.  Add a struct list_head to
> the union so it's clearly in use for pgds.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
>  include/linux/mm_types.h | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 4aba6c0c2ba8..9bb34e2cd5a5 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -142,8 +142,13 @@ struct page {
>  			struct list_head deferred_list;
>  		};
>  		struct {	/* Page table pages */
> -			unsigned long _pt_pad_1;	/* compound_head */
> -			pgtable_t pmd_huge_pte; /* protected by page->ptl */
> +			union {
> +				struct list_head pgd_list;	/* x86 */

Shouldn't pgd_list_{add,del}() use this list head variable instead of lru to
complete the documentation?

Probably the list iteration loops arch/x86/* as well?

Ira

> +				struct {
> +					unsigned long _pt_pad_1;
> +					pgtable_t pmd_huge_pte;
> +				};
> +			};
>  			unsigned long _pt_pad_2;	/* mapping */
>  			union {
>  				struct mm_struct *pt_mm; /* x86 pgds only */
> -- 
> 2.26.2
> 
>