[PATCH] mm: Improve documentation of page_order v2

Developers occasionally try and optimise PFN scanners by using page_order but miss that in general it requires zone->lock. This has happened twice for compaction.c and rejected both times. This patch clarifies the documentation of page_order and adds a note to compaction.c why page_order is not

[PATCH] mm: Improve documentation of page_order v2

Developers occasionally try and optimise PFN scanners by using page_order but miss that in general it requires zone-lock. This has happened twice for compaction.c and rejected both times. This patch clarifies the documentation of page_order and adds a note to compaction.c why page_order is not