The behavior of Windows Server AppFabric 1.1 memory consumption is puzzling to many people. You may observe that the DistributedCacheService.exe consumes a large amount of memory even when the total size of objects stored in the cache is really small, the memory consumption is creeping up over time and can reach twice as much as the configured host cache size.
The behavior is expected if it is AppFabric 1.1. The memory management has changed from 1.0 to 1.1. AppFabric 1.1 manages the memory as its own pools. It adds the released memory to its own free pools but would not give back to GC. That is the reason why the memory usage on the OS level can be high and keeps climbing.
You can validate no memory leak by pushing additional data into the cache when the memory usage of DistributedCacheService.exe is already high or close to the configured host cache size. If AppFabric is able to accommodate, then you know AppFabric is managing it well.
By default, the amount of memory reserved for the cache on a given server is 50% of the total RAM. The host size in MB is available caching memory on the cache host. This only accounts for items in the cache and not the memory used for the caching service itself. You can configure it lower, but configuring the amount higher is not supported
Additional info on AppFabric 1.1 memory management: