linux-kernel - Re: [PATCH] hugetlb: clear PG_reserved before setting PG

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Message-ID: <004e01d10596$eba6de70$c2f49b50$@alibaba-inc.com>
Date:	Tue, 13 Oct 2015 17:09:52 +0800
From:	"Hillf Danton" <hillf.zj@...baba-inc.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Sasha Levin" <sasha.levin@...cle.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH] hugetlb: clear PG_reserved before setting PG_head on gigantic pages

> PF_NO_COMPOUND for PG_reserved assumes we don't use PG_reserved for
> compound pages. And we generally don't. But during allocation of
> gigantic pages we set PG_head before clearing PG_reserved and
> __ClearPageReserved() steps on the VM_BUG_ON_PAGE().
> 
> The fix is trivial: set PG_head after PG_reserved.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reported-by: Sasha Levin <sasha.levin@...cle.com>
> ---

Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>
> 
> Andrew, this patch can be folded into "page-flags: define PG_reserved behavior on compound pages".
> 
> ---
>  mm/hugetlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 6ecf61ffa65d..bd3f3e20313b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1258,8 +1258,8 @@ static void prep_compound_gigantic_page(struct page *page, unsigned int order)
> 
>  	/* we rely on prep_new_huge_page to set the destructor */
>  	set_compound_order(page, order);
> -	__SetPageHead(page);
>  	__ClearPageReserved(page);
> +	__SetPageHead(page);
>  	for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
>  		/*
>  		 * For gigantic hugepages allocated through bootmem at
> --
> 2.5.3
> 


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