On Fri, Nov 20, 2015 at 11:06:46AM +0100, Vlastimil Babka wrote: > On 11/20/2015 10:33 AM, Aaron Lu wrote: > >On 11/20/2015 04:55 PM, Aaron Lu wrote: > >>On 11/19/2015 09:29 PM, Vlastimil Babka wrote: > >>>+CC Andrea, David, Joonsoo > >>> > >>>On 11/19/2015 10:29 AM, Aaron Lu wrote: > >>>>The vmstat and perf-profile are also attached, please let me know if you > >>>>need any more information, thanks. > >>> > >>>Output from vmstat (the tool) isn't much useful here, a periodic "cat > >>>/proc/vmstat" would be much better. > >> > >>No problem. > >> > >>>The perf profiles are somewhat weirdly sorted by children cost (?), but > >>>I noticed a very high cost (46%) in pageblock_pfn_to_page(). This could > >>>be due to a very large but sparsely populated zone. Could you provide > >>>/proc/zoneinfo? > >> > >>Is a one time /proc/zoneinfo enough or also a periodic one? > > > >Please see attached, note that this is a new run so the perf profile is > >a little different. > > > >Thanks, > >Aaron > > Thanks. > > DMA32 is a bit sparse: > > Node 0, zone DMA32 > pages free 62829 > min 327 > low 408 > high 490 > scanned 0 > spanned 1044480 > present 495951 > managed 479559 > > Since the other zones are much larger, probably this is not the > culprit. But tracepoints should tell us more. I have a theory that > updating free scanner's cached pfn doesn't happen if it aborts due > to need_resched() during isolate_freepages(), before hitting a valid > pageblock, if the zone has a large hole in it. But zoneinfo doesn't Today, I revisit this issue and yes, I think that your theory is right. isolate_freepages() will not update cached pfn until call isolate_freepages_block(). So, if there are many holes or many unmovable pageblocks or !isolation_suitable() pageblocks, cached pfn will not updated if compaction aborts due to need_resched(). zoneinfo shows that there is not much holes so I guess that this problem is caused by latter two cases. It is better to update cached pfn in these cases. Although I don't see your solution yet, I guess it will help here. 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>