linux-kernel - Re: [PATCH] mm/page_alloc: Restrict and formalize compound_page

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Date:   Mon, 18 May 2020 12:05:21 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: Restrict and formalize
 compound_page_dtors[]

On 18.05.20 11:59, Anshuman Khandual wrote:
> Restrict elements in compound_page_dtors[] array per NR_COMPOUND_DTORS and
> explicitly position them according to enum compound_dtor_id. This improves
> protection against possible misalignment between compound_page_dtors[] and
> enum compound_dtor_id later on.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  include/linux/mm.h |  2 +-
>  mm/page_alloc.c    | 10 +++++-----
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 688558c57751..d1bd7736a5e5 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -856,7 +856,7 @@ enum compound_dtor_id {
>  #endif
>  	NR_COMPOUND_DTORS,
>  };
> -extern compound_page_dtor * const compound_page_dtors[];
> +extern compound_page_dtor * const compound_page_dtors[NR_COMPOUND_DTORS];
>  
>  static inline void set_compound_page_dtor(struct page *page,
>  		enum compound_dtor_id compound_dtor)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cef05d3a23f5..2e4c23b34940 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -302,14 +302,14 @@ const char * const migratetype_names[MIGRATE_TYPES] = {
>  #endif
>  };
>  
> -compound_page_dtor * const compound_page_dtors[] = {
> -	NULL,
> -	free_compound_page,
> +compound_page_dtor * const compound_page_dtors[NR_COMPOUND_DTORS] = {
> +	[NULL_COMPOUND_DTOR] = NULL,
> +	[COMPOUND_PAGE_DTOR] = free_compound_page,
>  #ifdef CONFIG_HUGETLB_PAGE
> -	free_huge_page,
> +	[HUGETLB_PAGE_DTOR] = free_huge_page,
>  #endif
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	free_transhuge_page,
> +	[TRANSHUGE_PAGE_DTOR] = free_transhuge_page,
>  #endif
>  };
>  
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb