Re: [PATCH v4 1/4] mm/page_alloc: fix incorrect isolation behavior by rechecking migratetype

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

On Mon, Oct 27, 2014 at 11:33:20AM +0100, Vlastimil Babka wrote:
> On 10/23/2014 10:10 AM, Joonsoo Kim wrote:
> > Changes from v3:
> > Add one more check in free_one_page() that checks whether migratetype is
> > MIGRATE_ISOLATE or not. Without this, abovementioned case 1 could happens.
> 
> Good catch.
> 
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> 
> (minor suggestion below)
> 
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -749,9 +749,16 @@ static void free_one_page(struct zone *zone,
> >  	if (nr_scanned)
> >  		__mod_zone_page_state(zone, NR_PAGES_SCANNED, -nr_scanned);
> >  
> > +	if (unlikely(has_isolate_pageblock(zone) ||
> 
> Would it make any difference if this was read just once and not in each
> loop iteration?
> 
> 

I guess that you'd like to say this to patch 2.
I can do it, but, it doesn't any difference in terms of performance,
because we access zone's member variable in each loop iteration
in __free_one_page().

Thanks.

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