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

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Message-ID: <20200818032217.GA31960@L-31X9LVDL-1304.local>
Date:   Tue, 18 Aug 2020 11:22:17 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_reporting: the "page" must not be the list head

On Mon, Aug 17, 2020 at 09:05:32AM -0700, 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@...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.

Hi, Alexander,

I see you mentioned in the changelog, this change "mm/page_reporting: rotate
reported pages to the tail of the list" brings some performance gain.

Would you mind sharing more test detail? I would like to have a try at my
side.

Thanks :-)

-- 
Wei Yang
Help you, Help me