On 04/18/2014 10:26 AM, Andi Kleen wrote: > Mel Gorman <mgorman@xxxxxxx> writes: >> Favour the common case and disable it by default. Users that are >> sophisticated enough to know they need zone_reclaim_mode will detect it. > > While I'm not totally against this change, it will destroy many > carefully tuned configurations as the default NUMA behavior may be completely > different now. So it seems like a big hammer, and it's not even clear > what problem you're exactly solving here. I'm not 100% sure what the common case _is_. Folks who want good NUMA affinity are happy now and are happy by default. Folks who want to fill memory with page cache are mad and mad by default, and they're the ones complaining. It's hard to count the happy ones. :) But, on the other hand, the current situation is easy to debug. Someone complains that they have too much free memory, and it ends up being pretty easy to solve just looking at statistics, and things go horribly wrong quickly. If we apply this patch, it's much less obvious when things are going wrong, and we have no statistics to help. We'll need to get folks running more things like numatop: https://01.org/numatop That said, as a recipient of angry calls from customers who don't like zone_reclaim_mode, I _do_ think this is the path we should take at the moment. Maybe we'll be reverting it in a few years once all of our customers are angry about lack of NUMA locality. Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> -- 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>