Yes it will fill the entire memory with all kinds of stuff it can cache. If it needs memory for something it kicks out the cache to make room the thing it wants to store in memory.
Be aware that memory figures in tools like top and ps are not meant to be read as absolute values. They are meant to be interpreted and put into context. Otherwise they will give you wrong impressions.
Unless there is trouble or your an expert it is probably best to leave Linux memory management alone and let Linux do its job