mm, compaction: prevent VM_BUG_ON when terminating freeing scanner

It's possible to isolate some freepages in a pageblock and then fail
split_free_page() due to the low watermark check.  In this case, we hit
VM_BUG_ON() because the freeing scanner terminated early without a
contended lock or enough freepages.

This should never have been a VM_BUG_ON() since it's not a fatal
condition.  It should have been a VM_WARN_ON() at best, or even handled
gracefully.

Regardless, we need to terminate anytime the full pageblock scan was not
done.  The logic belongs in isolate_freepages_block(), so handle its
state gracefully by terminating the pageblock loop and making a note to
restart at the same pageblock next time since it was not possible to
complete the scan this time.

[[email protected]: don't rescan pages in a pageblock]
  Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: David Rientjes <[email protected]>
Reported-by: Minchan Kim <[email protected]>
Tested-by: Minchan Kim <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions