Yes, as mentioned, it is a very good feature if used correctly. Also keep the locked in cache a measured percentage of the overall memory. I have seen systems freeze up completely because of large locked caches.
Regards, Nikhils On Mon, Apr 13, 2009 at 11:20 PM, Matt Ingenthron <[email protected]> wrote: > > Qiangning Hong wrote: > >> The manpage says: >> -k Lock down all paged memory. This is a somewhat >> dangerous option >> with large caches, so consult the README and memcached >> homepage >> for configuration suggestions. >> >> README says: >> Also, be warned that the -k (mlockall) option to memcached might be >> dangerous when using a large cache. Just make sure the memcached >> machines >> don't swap. memcached does non-blocking network I/O, but not disk. >> (it >> should never go to disk, or you've lost the whole point of it) >> >> Why locking pages in memory considered dangerous? It can avoid >> swapping, so that keep a good response time. Doesn't it a good >> feature? >> >> > > It's likely considered dangerous due to the impact it can have on other > applications running on the same system, or components of the OS. As you > say, it is a good feature if used correctly. > If you have, for instance, your application running on the same system and > have a peak in user requests, it can lead to a situation where that > application has memory needs and cannot get any more memory. Even though > your cache could have a low response time, the overall user experience can > be quite low. > > I've recommended this flag to others in the past, and I'd just recommend > start conservative (without creating too large a cache), monitor the > environment, and tune from there. > > Hope that helps, > > - Matt >
