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

[Alexander Duyck]

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@xxxxxxxxxxxxxxxxx>
> > ---
> >   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.