[Devel] [PATCH -mm v2 1/2] mem-hotplug: implement get/put_online_mems

[Andrew Morton]

On Mon, 7 Apr 2014 13:45:34 +0400 Vladimir Davydov <vdavydov at parallels.com> wrote:

> {un}lock_memory_hotplug, which is used to synchronize against memory
> hotplug, is currently backed by a mutex, which makes it a bit of a
> hammer - threads that only want to get a stable value of online nodes
> mask won't be able to proceed concurrently. Also, it imposes some strong
> locking ordering rules on it, which narrows down the set of its usage
> scenarios.
> 
> This patch introduces get/put_online_mems, which are the same as
> get/put_online_cpus, but for memory hotplug, i.e. executing a code
> inside a get/put_online_mems section will guarantee a stable value of
> online nodes, present pages, etc.

Well that seems a nice change.  I added the important paragraph

"lock_memory_hotplug()/unlock_memory_hotplug() are removed altogether."

I'll Cc a large number of people who have recently worked on the memory
hotplug code.  Hopefully some of them will have time to review and test
these patches, thanks.