tree aafa5169cde98a2bb8327fcc948c76dba0746322
parent 7e325d3a6b117c7288bfc0755410e9d9d2b71326
author Al Viro <viro@zeniv.linux.org.uk> 1245823518 -0400
committer Al Viro <viro@zeniv.linux.org.uk> 1245845725 -0400

Make allocation of anon devices cheaper

Standard trick - add a new variable (start) such that
for each n < start n is known to be busy.  Allocation can
skip checking everything in [0..start) and if it returns
n, we can set start to n + 1.  Freeing below start sets
start to what we'd just freed.

Of course, it still sucks if we do something like
	free 0
	allocate
	allocate
in a loop - still O(n^2) time.  However, on saner loads it
improves the things a lot and the entire thing is not worth
the trouble of switching to something with better worst-case
behaviour.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>