linux-kernel - Re: [PATCH 1/2] mm/memory-failure.c: PageHuge is handled at the beginning of memory

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Date:   Tue, 19 Nov 2019 13:23:54 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>,
        n-horiguchi@...jp.nec.com, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/memory-failure.c: PageHuge is handled at the
 beginning of memory_failure

On 18.11.19 09:20, Wei Yang wrote:
> PageHuge is handled by memory_failure_hugetlb(), so this case could be
> removed.
> 
> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
> ---
>   mm/memory-failure.c | 5 +----
>   1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 3151c87dff73..392ac277b17d 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1359,10 +1359,7 @@ int memory_failure(unsigned long pfn, int flags)
>   	 * page_remove_rmap() in try_to_unmap_one(). So to determine page status
>   	 * correctly, we save a copy of the page flags at this time.
>   	 */
> -	if (PageHuge(p))
> -		page_flags = hpage->flags;
> -	else
> -		page_flags = p->flags;
> +	page_flags = p->flags;
>   
>   	/*
>   	 * unpoison always clear PG_hwpoison inside page lock
> 

I somewhat miss a proper explanation why this is safe to do. We access 
page flags here, so why is it safe to refer to the ones of the sub-page?

-- 

Thanks,

David / dhildenb