Its fine probably. Mine has 0.5G as cache.
This is what I found on internet
What's going on?
Linux is borrowing unused memory for disk caching. This makes it looks like you are low on memory, but you are not! Everything is fine!
If your applications want more memory, they just take back a chunk that the disk cache borrowed. Disk cache can always be given back to applications immediately! You are not low on ram!