A fast "list" data structure, which is actually a radix tree, with an
IDA for slot allocation and a percpu buffer on top of that.
Items cannot be added or moved to the head or tail, only added at some
(arbitrary) position and removed. The advantage is that adding, removing
and iteration is generally lockless, only hitting the lock in ida when
the percpu buffer is full or empty.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>