[PATCH] mm: separate move/undo parts from migrate_pages_batch()

[Byungchul Park]

Hi,

This is a part of luf(lazy unmap flush) patchset and also referred
several times by e.g. Shivank Garg and Zi Yan who are currently working
on page migration optimization.  Why don't we take this first so that
such a migration optimization tries can use it.

	Byungchul

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