On Sun, Nov 14, 2010 at 03:02:03PM +0900, KOSAKI Motohiro wrote: > > On Thu, Nov 11, 2010 at 07:07:04PM +0000, Mel Gorman wrote: > > > + if (COMPACTION_BUILD) > > > + sc->lumpy_reclaim_mode = LUMPY_MODE_COMPACTION; > > > + else > > > + sc->lumpy_reclaim_mode = LUMPY_MODE_CONTIGRECLAIM; > > > > > > > Gack, I posted the slightly wrong version. This version prevents lumpy > > reclaim ever being used. The figures I posted were for a patch where > > this condition looked like > > > > if (COMPACTION_BUILD && priority > DEF_PRIORITY - 2) > > sc->lumpy_reclaim_mode = LUMPY_MODE_COMPACTION; > > else > > sc->lumpy_reclaim_mode = LUMPY_MODE_CONTIGRECLAIM; > > Can you please tell us your opinition which is better 1) automatically turn lumby on > by priority (this approach) 2) introduce GFP_LUMPY (andrea proposed). I'm not > sure which is better, then I'd like to hear both pros/cons concern. > That's a very good question! The main "pro" of using lumpy reclaim is that it has been tested. It's known to be very heavy and disrupt the system but it's also known to work. Lumpy reclaim is also less suspectible to allocation races than compaction is i.e. if memory is low, compaction requires that X number of pages be free where as lumpy frees the pages it requires. GFP_LUMPY is something else and is only partially related. Transparent Huge Pages (THP) does not want to hit lumpy reclaim no matter what the circumstances are - It is always better for THP to not use lumpy reclaim. It's debatable whether it should even reclaim order-0 pages for compaction so even with this series, THP might still introduce GFP_LUMPY. Does this answer your question? -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>