On 2015-09-10 18:45:06 +0200, Andrea Arcangeli wrote: > On Mon, Aug 24, 2015 at 08:46:11PM +0000, James Hartshorn wrote: > > Some more links to discussion > > about THP: Postgresql https://lwn.net/Articles/591723/ Postgresql > > http://www.postgresql.org/message-id/20120821131254.1415a545@xxxxxxxxxxxxxxxxxxxx > > "and my interpretation was that it was trying to create hugepages from > scattered fragments" > > This is a very old email, but I'm just taking it as an example because > this has to be a compaction issue. If you run into very visible hangs > that goes away by disabling THP, it can't be THP to blame. THP can > increase the latency jitter during page faults (real time sensitive > application could notice a 2MB clear_page vs a 4KB clear_page), but > not in a way that hangs a system and becomes visible to the user. > > It's just very early compaction code was too aggressive and it got > fixed in the meanwhile. There's still some slowdown (as of 4.0) in extreme postgres workloads with THP and/or compaction enabled, but I've indeed not been able to reproduce bad stalls or large (10%+) slowdowns with recent kernels. 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>