Re: NUMA zone_reclaim_mode

[Dan Van Der Ster <daniel.vanderster@xxxxxxx>]

On 12 Jan 2015, at 17:08, Sage Weil <sage@xxxxxxxxxxxx> wrote:

On Mon, 12 Jan 2015, Dan Van Der Ster wrote:

Moving forward, I think it would be good for Ceph to a least document
this behaviour, but better would be to also detect when
zone_reclaim_mode != 0 and warn the admin (like MongoDB does). This
line from the commit which disables it in the kernel is pretty wise,
IMHO: "On current machines and workloads it is often the case that
zone_reclaim_mode destroys performance but not all users know how to
detect this. Favour the common case and disable it by default."

Sounds good to me.  Do you mind submitting a patch that prints a warning
from either FileStore::_detect_fs()?  That will appear in the local
ceph-osd.NNN.log.

Alternatively, we should send something to the cluster log
(osd->clog.warning() << "...") but if we go that route we need to be
careful that the logger it up and running first, which (I think) rules out
FileStore::_detect_fs().  It could go in OSD itself although that seems
less clean since the recommendation probably doesn't apply when
using a backend that doesn't use a file system…

Sure, I’ll try to prepare a patch which warns but isn’t too annoying. MongoDB already solved the heuristic:

https://github.com/mongodb/mongo/blob/master/src/mongo/db/startup_warnings_mongod.cpp

It’s licensed as AGPLv3 -- do you already know if we can borrow such code into Ceph?

Cheers, Dan

Thanks!
sage

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