[RFC] change non-atomic bitops method

[David Miller]

From: Andrew Morton <akpm at linux-foundation.org>
Date: Mon, 2 Feb 2015 22:38:51 -0800

> It is only with both these ratios that we can work out whether the
> patch is a net gain.  My suspicion is that set_bit on an already-set
> bit is so rare that the patch will be a loss.

A common pattern is implementing a "referenced" bit, and in that case
the bit is often already set, and in such a scenerio the proposed
change is a huge win.