mm: fs: invalidate BH LRU during page migration

mm: fs: invalidate BH LRU during page migration

Pages containing buffer_heads that are in one of the per-CPU buffer_head
LRU caches will be pinned and thus cannot be migrated.  This can prevent
CMA allocations from succeeding, which are often used on platforms with
co-processors (such as a DSP) that can only use physically contiguous
memory.  It can also prevent memory hot-unplugging from succeeding,
which involves migrating at least MIN_MEMORY_BLOCK_SIZE bytes of memory,
which ranges from 8 MiB to 1 GiB based on the architecture in use.

Correspondingly, invalidate the BH LRU caches before a migration starts
and stop any buffer_head from being cached in the LRU caches, until
migration has finished.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Minchan Kim <[email protected]>
Reported-by: Chris Goldsworthy <[email protected]>
Reported-by: Laura Abbott <[email protected]>
Tested-by: Oliver Sang <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: John Dias <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>