Recently I'm reading "Professional Linux Kernel Architecture" while referencing the source code of kernel 2.6.24 and I have a question about priority search tree.
In prio_tree_init function (http://lxr.free-electrons.com/source/lib/prio_tree.c?v=2.6.24#L71), array index_bits_to_maxindex is initialized to 1,3,7,15,31...2^(i+1)-1. I don't know why it is initialized to these numbers and what is the relationship between index_bits_to_maxindex and prio_tree_root->index_bits.