Re: [RFC PATCH v3 1/4] mm/page_alloc: fix incorrect isolation behavior by rechecking migratetype

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

On Mon, Sep 08, 2014 at 10:31:29AM +0200, Vlastimil Babka wrote:
> On 08/26/2014 10:08 AM, Joonsoo Kim wrote:
> 
> >diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >index f86023b..51e0d13 100644
> >--- a/mm/page_alloc.c
> >+++ b/mm/page_alloc.c
> >@@ -740,9 +740,15 @@ 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))) {
> >+		migratetype = get_pfnblock_migratetype(page, pfn);
> >+		if (is_migrate_isolate(migratetype))
> >+			goto skip_counting;
> >+	}
> >+	__mod_zone_freepage_state(zone, 1 << order, migratetype);
> >+
> >+skip_counting:
> 
> Here, wouldn't a simple 'else __mod_zone_freepage_state...' look
> better than goto + label? (same for the following 2 patches). Or
> does that generate worse code?

To remove goto label, we need two __mod_zone_freepage_state() like
as below. On my system, it doesn't generate worse code, but, I am not
sure that this is true if more logic would be added. I think that
goto + label is better.

+	if (unlikely(has_isolate_pageblock(zone))) {
+		migratetype = get_pfnblock_migratetype(page, pfn);
+               if (!is_migrate_isolate(migratetype))
+                       __mod_zone_freepage_state(zone, 1 << order, migratetype);
+       } else {
+               __mod_zone_freepage_state(zone, 1 << order, migratetype);
        }

Anyway, What do you think which one is better, either v2 or v3? Still, v3? :)

Thanks.

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