mm, compaction: make fast_isolate_freepages() stay within zone
Compaction always operates on pages from a single given zone when isolating both pages to migrate and freepages. Pageblock boundaries are intersected with zone boundaries to be safe in case zone starts or ends in the middle of pageblock. The use of pageblock_pfn_to_page() protects against non-contiguous pageblocks. The functions fast_isolate_freepages() and fast_isolate_around() don't currently protect the fast freepage isolation thoroughly enough against these corner cases, and can result in freepage isolation operate outside of zone boundaries: - in fast_isolate_freepages() if we get a pfn from the first pageblock of a zone that starts in the middle of that pageblock, 'highest' can be a pfn outside of the zone. If we fail to isolate anything in this function, we may then call fast_isolate_around() on a pfn outside of the zone and there effectively do a set_pageblock_skip(page_to_pfn(highest)) which may currently hit a...
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