Last year I gave a talk extolling the benefits of the Linux radix tree. This year I am talking about its shortcomings, what I did to improve things, and how I came to the conclusion that it had to be replaced.

The new XArray is easier to use than the radix tree. Conceptually, it is an array of 16 quintillion pointers, all of which are initially NULL. Just like an array, its basic operations are 'load' and 'store', unlike a tree's 'lookup', 'insert' and 'delete'. It provides some more advanced operations, and enables users to build their own operations.

This talk covers general aspects of API design for C programmers, as well as particular considerations for kernel API design due to the constrained environment.