Memcached uses a simple Least Recently Used (LRU) eviction policy to manage memory usage when the cache reaches its maximum capacity. The LRU eviction policy evicts the least recently accessed items from the cache to make room for new data. When new data needs to be stored in the cache and the cache is full, Memcached identifies the least recently accessed item (i.e., the item that has not been accessed for the longest time) and removes it from the cache to free up space.

The LRU eviction policy helps ensure that the most frequently accessed items remain in the cache while less frequently accessed items are evicted to make room for new data. This helps optimize cache performance by maximizing the likelihood of cache hits for frequently accessed data.

It's important to note that Memcached does not support configurable eviction policies out of the box. However, some third-party Memcached distributions or middleware solutions may offer additional eviction policies or customization options for managing cache eviction behavior. Additionally, developers can implement custom eviction logic within their applications to handle cache eviction based on specific criteria or application requirements.