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Subject: Re: [PATCH] mm/page_reporting: the "page" must not be the list head
To:     Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Wei Yang <richard.weiyang@linux.alibaba.com>,
        akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20200817084836.29216-1-richard.weiyang@linux.alibaba.com>
 <fa97519b-a860-5fea-9511-2237f195caeb@redhat.com>
 <aaa56d83-2444-d74e-025a-508a2be6b772@linux.intel.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <c362eb24-d4bc-82e8-e813-0951ce50b440@redhat.com>
Date:   Mon, 17 Aug 2020 19:07:04 +0200
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On 17.08.20 18:05, Alexander Duyck wrote:
> 
> 
> On 8/17/2020 2:35 AM, David Hildenbrand wrote:
>> On 17.08.20 10:48, Wei Yang wrote:
>>> If "page" is the list head, list_for_each_entry_safe() would stop
>>> iteration.
>>>
>>> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
>>> ---
>>>   mm/page_reporting.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/mm/page_reporting.c b/mm/page_reporting.c
>>> index 3bbd471cfc81..aaaa3605123d 100644
>>> --- a/mm/page_reporting.c
>>> +++ b/mm/page_reporting.c
>>> @@ -178,7 +178,7 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
>>>   		 * the new head of the free list before we release the
>>>   		 * zone lock.
>>>   		 */
>>> -		if (&page->lru != list && !list_is_first(&page->lru, list))
>>> +		if (!list_is_first(&page->lru, list))
>>>   			list_rotate_to_front(&page->lru, list);
>>>   
>>>   		/* release lock before waiting on report processing */
>>>
>>
>> Is this a fix or a cleanup? If it's a fix, can this be reproduced easily
>> and what ere the effects?
>>
> 
> This should be a clean-up. Since the &page->lru != list will always be true.
> 

Makes sense, maybe we can make that a little bit clearer in the patch
description.

> If I recall at some point the that was a check for &next->lru != list 
> but I think I pulled out an additional conditional check somewhere so 
> that we just go through the start of the loop again and iterate over 
> reported pages until we are guaranteed to have a non-reported page to 
> rotate to the top of the list with the general idea being that we wanted 
> the allocator to pull non-reported pages before reported pages.

-- 
Thanks,

David / dhildenb