Hi Minchan, On Thu, Aug 15, 2013 at 11:10:04PM +0900, Minchan Kim wrote: >On Thu, Aug 15, 2013 at 02:56:27PM +0100, Mel Gorman wrote: >> On Thu, Aug 15, 2013 at 10:41:39PM +0900, Minchan Kim wrote: >> > Hey Mel, >> > >> > On Thu, Aug 15, 2013 at 11:47:27AM +0100, Mel Gorman wrote: >> > > On Thu, Aug 15, 2013 at 06:02:53PM +0800, Hillf Danton wrote: >> > > > If the allocation order is not high, direct compaction does nothing. >> > > > Can we skip compaction here if order drops to zero? >> > > > >> > > >> > > If the allocation order is not high then >> > > >> > > pgdat_needs_compaction == (order > 0) == false == no calling compact_pdatt >> > > >> > > In the case where order is reset to 0 due to fragmentation then it does >> > > call compact_pgdat but it does no work due to the cc->order check in >> > > __compact_pgdat. >> > > >> > >> > I am looking at mmotm-2013-08-07-16-55 but couldn't find cc->order >> > check right before compact_zone in __comact_pgdat. >> > Could you pinpoint code piece? >> > >> >> Thanks, I screwed up as that check happens too late. However, it still >> ends up not mattering because it does this >> >> compact_pgdat >> -> __compact_pgdat >> -> compact_zone >> -> compaction_suitable >> >> For order == 0, compaction_suitable will return either COMPACT_SKIPPED >> (if the watermarks are not met) and COMPACT_PARTIAL otherwise. Either >> way, compaction doesn't run. > >In compaction_suitable, it could pass first zone_watermark_ok >but failed second zone_watermark_ok while fragindex is -1000 >so compaction could run. > I'm not sure why you said that second zone_watermark_ok failed while fragindex is -1000, actually they are the same check against order 0. First: watermark = low_wmark_pages(zone) + (2UL << order); zone_watermark_ok(zone, 0, watermark, 0, 0); Second: fragindex == -1000 && zone_watermark_ok(zone, order, watermark, 0, 0) Both COMPACT_SKIPPED and COMPACT_PARTIAL will fail compaction. Regards, Wanpeng Li >And we shouldn't depend on such coincidence. > > >> >> -- >> Mel Gorman >> SUSE Labs >> >> -- >> 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> > >-- >Kind regards, >Minchan Kim > >-- >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> -- 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>