Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
From: David Hildenbrand <david@redhat.com>
To: Wei Yang <richardw.yang@linux.intel.com>
Cc: n-horiguchi@ah.jp.nec.com, akpm@linux-foundation.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	James Morse <james.morse@arm.com>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH 1/2] mm/memory-failure.c: PageHuge is handled at the beginning of memory_failure
Date: Wed, 20 Nov 2019 16:04:44 +0100
Message-ID: <a85053b7-9298-9dd3-3826-e63cf8c7bd81@redhat.com> (raw)
In-Reply-To: <20191120004620.GB11061@richard>

On 20.11.19 01:46, Wei Yang wrote:
> 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@linux.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.

Oh wait, I think I missed the check right at the beginning of this 
function, sorry :/

Sooo, memory_failure_hugetlb() was introduced by

commit 761ad8d7c7b5485bb66fd5bccb58a891fe784544
Author: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Date:   Mon Jul 10 15:47:47 2017 -0700

     mm: hwpoison: introduce memory_failure_hugetlb()

and essentially ripped out all PageHuge() checks *except* this check. 
This check was introduced in

commit 7258ae5c5a2ce2f5969e8b18b881be40ab55433d
Author: James Morse <james.morse@arm.com>
Date:   Fri Jun 16 14:02:29 2017 -0700

     mm/memory-failure.c: use compound_head() flags for huge pages


Maybe that was just a merge oddity as both commits are only ~1month 
apart. IOW, I think Naoya's patch forgot to rip it out.


Can we make this clear in the patch description like "This is dead code 
that cannot be reached after commit 761ad8d7c7b5 ("mm: hwpoison: 
introduce memory_failure_hugetlb()")"

I assume Andrew can fix up when applying

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

-- 

Thanks,

David / dhildenb



  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-18  8:20 Wei Yang
2019-11-18  8:20 ` [PATCH 2/2] mm/memory-failure.c: not necessary to recalculate hpage Wei Yang
2019-11-20 15:07   ` David Hildenbrand
2019-11-21  1:05     ` Wei Yang
2019-12-02 22:28     ` Wei Yang
2019-12-05 15:06       ` David Hildenbrand
2019-12-06  1:48         ` Wei Yang
2020-01-08 12:20           ` David Hildenbrand
2020-01-09  1:58             ` Wei Yang
2019-11-19 12:23 ` [PATCH 1/2] mm/memory-failure.c: PageHuge is handled at the beginning of memory_failure David Hildenbrand
2019-11-20  0:46   ` Wei Yang
2019-11-20 15:04     ` David Hildenbrand [this message]
2019-11-21  1:07       ` Wei Yang

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=a85053b7-9298-9dd3-3826-e63cf8c7bd81@redhat.com \
    --to=david@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=james.morse@arm.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=n-horiguchi@ah.jp.nec.com \
    --cc=richardw.yang@linux.intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org
	public-inbox-index linux-mm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git