Hi Dan, On 12/01/2015 17:25, Dan Van Der Ster wrote: > >> On 12 Jan 2015, at 17:08, Sage Weil <sage@xxxxxxxxxxxx <mailto: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? If you're looking at adapting the https://github.com/mongodb/mongo/blob/master/src/mongo/db/startup_warnings_mongod.cpp#L107 code block and a few others into Ceph the licensing terms do not apply. If you were to disregard the mongodb implementation and rewrite it from scratch, you would come up with the same code because there is no way to do it differently. A contrario, if the licensing terms were to be applied, every implementation recommending that /proc/sys/vm/zone_reclaim_mode is set to zero would always be under AGPLv3 because they are all a) reading the file, b) printing a warning. That would not make sense and this is why software implementing a trivial logic can't be copyrighted. In my opinion you can borrow code from startup_warnings_mongod.cpp into Ceph because it's trivial and non copyrightable. Cheers > > Cheers, Dan > > >> Thanks! >> sage > > > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > -- Loïc Dachary, Artisan Logiciel Libre
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