Recently, Robert Mueller reported zone_reclaim_mode doesn't work
properly on his new NUMA server (Dual Xeon E5520 + Intel S5520UR MB).
He is using Cyrus IMAPd and it's built on a very traditional
single-process model.
Let's add Robert to the cc to see if this is still an issue, it hasn't
been re-reported in over six months.
We definitely still set this in /etc/sysctl.conf on every imap server
machine:
vm.zone_reclaim_mode = 0
I believe it still defaults to 1 otherwise. What I haven't tested is if
leaving it at 1 still causes problems. It definitely DID previously cause
big problems (I think that was around 2.6.34 or so).
http://blog.fastmail.fm/2010/09/15/default-zone_reclaim_mode-1-on-numa-kernel-is-bad-for-fileemailweb-servers/
I'll try changing it to 1 on a machine for 4 hours, see if it makes a
noticeable difference and report back.
Rob
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