linux-kernel - Re: [PATCH] hugetlb: remove unnecessary set_page_count in prep_compound_gigantic

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Message-ID: <YXjpDoa9yvtlBuJl@localhost.localdomain>
Date:   Wed, 27 Oct 2021 07:52:14 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pasha Tatashin <pasha.tatashin@...een.com>
Subject: Re: [PATCH] hugetlb: remove unnecessary set_page_count in
 prep_compound_gigantic_page

On Tue, Oct 26, 2021 at 03:06:35PM -0700, Mike Kravetz wrote:
> In commit 7118fc2906e29 ("hugetlb: address ref count racing in
> prep_compound_gigantic_page"), page_ref_freeze is used to atomically
> zero the ref count of tail pages iff they are 1.  The unconditional
> call to set_page_count(0) was left in the code.  This call is after
> page_ref_freeze so it is really a noop.
> 
> Remove redundant and unnecessary set_page_count call.
> 
> Fixes: 7118fc2906e29 ("hugetlb: address ref count racing in prep_compound_gigantic_page")
> Suggested-by: Pasha Tatashin <pasha.tatashin@...een.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

> ---
>  mm/hugetlb.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 906fe8a3b93d..88047a367080 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1795,7 +1795,6 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order,
>  		} else {
>  			VM_BUG_ON_PAGE(page_count(p), p);
>  		}
> -		set_page_count(p, 0);
>  		set_compound_head(p, page);
>  	}
>  	atomic_set(compound_mapcount_ptr(page), -1);
> -- 
> 2.31.1
> 
> 

-- 
Oscar Salvador
SUSE Labs