linux-kernel - Re: [PATCH] mm/page_reporting: the "page" must not be the list head

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Date:   Mon, 17 Aug 2020 09:05:32 -0700
From:   Alexander Duyck <alexander.h.duyck@...ux.intel.com>
To:     David Hildenbrand <david@...hat.com>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_reporting: the "page" must not be the list head



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@...ux.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.

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.