On Tue, 2008-11-04 at 17:34 +0100, Rafael J. Wysocki wrote:
> Now, I need to do one more thing, which is to check how much memory has to be
> freed before creating the image.  For this purpose I need to lock memory
> hotplug temporarily, count pages to free and unlock it.  What interface should
> I use for this purpose? 
> 
> [I'll also need to lock memory hotplug temporarily during resume.]

We currently don't have any big switch to disable memory hotplug, like
lock_memory_hotplug() or something. :)

If you are simply scanning and counting pages, I think the best thing to
use would be the zone_span_seq*() seqlock stuff.  Do your count inside
the seqlock's while loop.  That covers detecting a zone changing while
it is being scanned.

The other case to detect is when a new zone gets added.  These are
really rare.  Rare enough that we actually use a stop_machine() call in
build_all_zonelists() to do it.  All you would have to do is detect when
one of these calls gets made.  I think that's a good application for a
new seq_lock.

I've attached an utterly untested patch that should do the trick.
Yasunori and KAME should probably take a look at it since the node
addition code is theirs.

-- Dave