What happens when a MemoryCache object exceeds its CacheMemoryLimit?

When an instanc开发者_Python百科e of System.Runtime.Caching.MemoryCache (.NET 4.0) exceeds its CacheMemoryLimit, are all cache entries removed, or just some of them?

Technically, it should just be some of them. However, I've had some issues with items not being evicted at all -- which I seem to have tracked down to the new garbage collection configuration options in .Net 4. It won't ever be all of them, though.