[PATCH 0/3] memory hotplug: updates and bugfix for is_removable

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

Problem:

/sys/devices/system/memory/memoryX/removable file shows whether the section
can be offlined or not. Returns "1" if it seems removable.

Now, the file uses a similar logic to one offline_pages() uses.
Problem here is.
 
  - removable detection logics of is_removable() and offline_pages() is
    different from each other.
  - The logic, which check MIGRATE_TYPE, tend to be incorrect once fragmented.
    MIGRATE_TYPE of a pageblock is just a hint, no guarantee.

Then, this patch set does.

  - use the same logic between is_removable() and offline_pages().
  - don't use MIGRATE_TYPE, check the memmap itself directly rather than hint.

Brief patch description:
 1. bugfix for is_removable() check. I think this should be back ported.
 2. bugfix for callback at counting immobile pages.
    I think the old logic rarely hits this bug..so, not necessary to backport.
 3. the unified new logic for is_remobable.

Only patch1 is CCed to stable for now and the patch series itself is onto
mmotm-08-27.

Thanks,
-Kame

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