On Fri, 11 Sep 2009, Doug Hughes wrote: > Suppose you have an application that makes a memory reservation, a large > memory reservation.. Enterprise databases and some CAD or EDA programs > have been known to do this. In such cases, it makes more sense to make
You're quite right that they do this but a reservation does not imply that memory or swap is actually being used. In a modern system a page fault will occur if the system asks for a memory page which has been reserved for the app but doesn't actually contain anything. The OS can then dynamically provision the page in real time. This is where overcommit comes in. If you allow for a large overcommit then you can run these apps without actually having to allocate large amounts of swap. The key reason for this is that they often don't use as much memory as they initially ask for. Of course if you allow overcommit and the app does demand it's full allocation then you're in OOM territory. Cheers, Rob -- I tried to change the world but they had a no-return policy http://www.practicalsysadmin.com _______________________________________________ Discuss mailing list [email protected] http://lopsa.org/cgi-bin/mailman/listinfo/discuss This list provided by the League of Professional System Administrators http://lopsa.org/
