tree 353b2064ab9a23cfd52a231e03e1dfeae9bfa283
parent 01ecdf32d657f9e19f84ba9785c9954734666a9c
author Dave Watson <davejwatson@fb.com> 1456329883 -0800
committer Jason Evans <je@fb.com> 1456525270 -0800

Use linear scan for small bitmaps

For small bitmaps, a linear scan of the bitmap is slightly faster than
a tree search - bitmap_t is more compact, and there are fewer writes
since we don't have to propogate state transitions up the tree.
On x86_64 with the current settings, I'm seeing ~.5%-1% CPU improvement
in production canaries with this change.

The old tree code is left since 32bit sizes are much larger (and ffsl
smaller), and maybe the run sizes will change in the future.

This resolves #339.