Why are items limited to 1 megabyte in size in Memcache?

Memcached's memory storage engine, uses a slabs approach to memory management. Memory is broken up into slabs chunks of varying sizes, starting at a minimum number and ascending by a factorial up to the largest possible value.

Say the minimum value is 400 bytes, and the maximum value is 1 megabyte, and the factorial is 1.20:

slab 1 - 400 bytes slab 2 - 480 bytes slab 3 - 576 bytes ... etc.

The larger the slab, the more of a gap there is between it and the previous slab. So the larger the maximum value the less efficient the memory storage is. Memcached also has to pre-allocate some memory for every slab that exists, so setting a smaller factorial with a larger max value will require even more overhead.