Re: [patch V2 2/2] mm/memory-hotplug: Switch locking to a percpu rwsem

From: Davidlohr Bueso
Date: Tue Jul 04 2017 - 11:22:21 EST

On Tue, 04 Jul 2017, Davidlohr Bueso wrote:

As a side effect you end up optimizing get/put_online_mems() at the cost
of more overhead for the actual hotplug operation, which is rare and of less
performance importance.

So nm this, the reader side actually gets _more_ expensive with pcpu-rwsems
due to at least two full barriers for each get/put operation.