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

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Message-ID: <20191120004620.GB11061@richard>
Date:   Wed, 20 Nov 2019 08:46:20 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        n-horiguchi@...jp.nec.com, akpm@...ux-foundation.org,
        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 Tue, Nov 19, 2019 at 01:23:54PM +0100, David Hildenbrand wrote:
>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?
>

Hi, David

I think your comment is on this line:

	page_flags = p->flags;

Maybe we need to use this:

	page_flags = hpage->flags;

And use hpage in the following or even the whole function?

While one thing interesting is not all "compound page" is PageCompound. For
some sub-page, we can't get the correct head. This means we may just check on
the sub-page.

>-- 
>
>Thanks,
>
>David / dhildenb

-- 
Wei Yang
Help you, Help me