On Tue, 29 Jul 2014, Vlastimil Babka wrote: > > I think there's two ways to go about it: > > > > - allow a single thp fault to be expensive and then rely on deferred > > compaction to avoid subsequent calls in the near future, or > > > > - try to make all thp faults be as least expensive as possible so that > > the cumulative effect of faulting large amounts of memory doesn't end > > up with lengthy stalls. > > > > Both of these are complex because of the potential for concurrent calls to > > memory compaction when faulting thp on several cpus. > > > > I also think the second point from that email still applies, that we > > should abort isolating pages within a pageblock for migration once it can > > no longer allow a cc->order allocation to succeed. > > That was the RFC patch 15, I hope to reintroduce it soon.
Which of the points above are you planning on addressing in another patch? I think the approach would cause the above to be mutually exclusive options. > You could still test > it meanwhile to see if you see the same extfrag regression as me. In my tests, > kswapd/khugepaged wasn't doing enough work to defragment the pageblocks that > the stress-highalloc benchmark (configured to behave like thp page fault) was > skipping. > The initial regression that I encountered was on a 128GB machine where async compaction would cause faulting 64MB of transparent hugepages to excessively stall and I don't see how kswapd can address this if there's no memory pressure and khugepaged can address it if it has the default settings which is very slow. Another idea I had is to only do async memory compaction for thp on local zones and avoid defragmenting remotely since, in my experimentation, remote thp memory causes a performance degradation over regular pages. If that solution were to involve zone_reclaim_mode and a test of node_distance() > RECLAIM_DISTANCE, I think that would be acceptable as well. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
