Ninja's_RGR'us (8/10/2011)
Eddie Wuerch (8/10/2011)
Having 512GB of memory lets me think you have a lot of CPUs in that box as well.If you're seeing loads of CMEMTHREAD waits in SQL Server 2008 R2 on ad-hoc compiles on a server with more than 16 CPU cores, you are likely suffering from a bug in R2. (We dealt with this on a 48-core box)
Update to the latest hotfix. If that doesn't solve it, you may need a specific hotfix from MS Support.
-Eddie
Do you have the kb link?
This looks similar, it may be the actual problem. I don't remember the particulars, but we did get the PSS hotfix around the time this KB article was published:
http://support.microsoft.com/kb/2492381
FIX: SQL Server 2008 R2 performs poorly when most threads wait for the CMEMTHREAD wait type if the threads use table variables or temp tables to load or update rowsets
Eddie Wuerch
MCM: SQL