On Fri, Oct 14, 2016 at 12:52:26PM +0200, Vlastimil Babka wrote: > On 10/14/2016 03:26 AM, Joonsoo Kim wrote: > >On Thu, Oct 13, 2016 at 11:12:10AM +0200, Vlastimil Babka wrote: > >>On 10/13/2016 10:08 AM, js1304@xxxxxxxxx wrote: > >>>From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > >>> > >>>When we try to find freepage in fallback buddy list, we always serach > >>>the largest one. This would help for fragmentation if we process > >>>unmovable/reclaimable allocation request because it could cause permanent > >>>fragmentation on movable pageblock and spread out such allocations would > >>>cause more fragmentation. But, movable allocation request is > >>>rather different. It would be simply freed or migrated so it doesn't > >>>contribute to fragmentation on the other pageblock. In this case, it would > >>>be better not to break the precious highest order freepage so we need to > >>>search the smallest freepage first. > >> > >>I've also pondered this, but then found a lower hanging fruit that > >>should be hopefully clear win and mitigate most cases of breaking > >>high-order pages unnecessarily: > >> > >>http://marc.info/?l=linux-mm&m=147582914330198&w=2 > > > >Yes, I agree with that change. That's the similar patch what I tried > >before. > > > >"mm/page_alloc: don't break highest order freepage if steal" > >http://marc.info/?l=linux-mm&m=143011930520417&w=2 > > Ah, indeed, I forgot about it and had to rediscover :) > > > > >> > >>So I would try that first, and then test your patch on top? In your > >>patch there's a risk that we make it harder for > >>unmovable/reclaimable pageblocks to become movable again (we start > >>with the smallest page which means there's lower chance that > >>move_freepages_block() will convert more than half of the block). > > > >Indeed, but, with your "count movable pages when stealing", risk would > >disappear. :) > > Hmm, but that counting is only triggered when we attempt to steal > whole pageblock. For movable allocation, can_steal_fallback() allows > that only for > (order >= pageblock_order / 2), and since your patch makes "order" > as small as possible for movable allocations, the chances are lower? Chances are lower than current but we eventually try to steal that (order >= pageblock_order / 2) freepage from unmovable pageblock and your logic will result in changing pageblock migratetype from unmovable to movable. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>