Messages in this thread | | | Date | Tue, 8 Apr 2014 16:26:42 +0200 | From | Andres Freund <> | Subject | Re: [PATCH 0/2] Disable zone_reclaim_mode by default |
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On 2014-04-08 09:17:04 -0500, Christoph Lameter wrote: > On Tue, 8 Apr 2014, Vlastimil Babka wrote: > > > On 04/08/2014 12:34 AM, Mel Gorman wrote: > > > When it was introduced, zone_reclaim_mode made sense as NUMA distances > > > punished and workloads were generally partitioned to fit into a NUMA > > > node. NUMA machines are now common but few of the workloads are NUMA-aware > > > and it's routine to see major performance due to zone_reclaim_mode being > > > disabled but relatively few can identify the problem. > > ^ I think you meant "enabled" here? > > > > Just in case the cover letter goes to the changelog... > > Correct. > > Another solution here would be to increase the threshhold so that > 4 socket machines do not enable zone reclaim by default. The larger the > NUMA system is the more memory is off node from the perspective of a > processor and the larger the hit from remote memory.
FWIW, I've the problem hit majorly on 8 socket machines. Those are the largest I have seen so far in postgres scenarios. Everything larger is far less likely to be used as single node database server, so that's possibly a sensible cutoff. But then, I'd think that special many-socket machines are setup by specialists, that'd know to enable if it makes sense...
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
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