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

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Date:   Tue, 28 Apr 2020 14:41:09 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org
Subject: Re: [PATCH 1/7] mm: Document x86 uses a linked list of pgds

On Tue, Apr 28, 2020 at 12:44:43PM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> 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@...radead.org>
> ---
>  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
> 
>