It's a bug in linux-next, but taking me too long to identify which commit is "to blame", so let me throw it over to you without more delay: I think __PageMovable() now needs to check !PageSlab(). I had made a small experimental change somewhere, rebuilt and rebooted, was not surprised to crash once swapping and compaction came in, but was surprised to find the crash in isolate_movable_page(), called by compaction's isolate_migratepages_block(). page->mapping was ffffffff811303aa, which qualifies as __PageMovable(), which expects struct movable_operations at page->mapping minus low bits. But ffffffff811303aa was the address of SLUB's rcu_free_slab(): I have CONFIG_CC_OPTIMIZE_FOR_SIZE=y, so function addresses may have low bits set. Over to you! Thanks, Hugh
