On 03/05/2015 05:52 PM, Andres Freund wrote: > Hi, > > On 2015-03-05 17:30:16 +0100, Vlastimil Babka wrote: >> That however means the workload is based on hugetlbfs and shouldn't trigger THP >> page fault activity, which is the aim of this patchset. Some more googling made >> me recall that last LSF/MM, postgresql people mentioned THP issues and pointed >> at compaction. See http://lwn.net/Articles/591723/ That's exactly where this >> patchset should help, but I obviously won't be able to measure this before LSF/MM... >> >> I'm CCing the psql guys from last year LSF/MM - do you have any insight about >> psql performance with THPs enabled/disabled on recent kernels, where e.g. >> compaction is no longer synchronous for THP page faults? > > What exactly counts as "recent" in this context? Most of the bigger > installations where we found THP to be absolutely prohibitive (slowdowns > on the order of a magnitude, huge latency spikes) unfortunately run > quite old kernels... I guess 3.11 does *not* count :/? That'd be a Yeah that's too old :/ 3.17 has patches to make compaction less aggressive on THP page faults, and 3.18 prevents khugepaged from holding mmap_sem during compaction, which could be also relevant. > bigger machine where I could relatively quickly reenable THP to check > whether it's still bad. I might be able to trigger it to be rebooted > onto a newer kernel, will ask. Thanks, that would be great, if you could do that. I also noticed that you now support hugetlbfs. That could be also interesting data point, if the hugetlbfs usage helped because THP code wouldn't trigger. Vlastimil > Greetings, > > Andres Freund > -- 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>