mm: compaction: do not mark unmovable pageblocks as skipped in async compaction

mm: compaction: do not mark unmovable pageblocks as skipped in async compaction

Compaction temporarily marks pageblocks where it fails to isolate pages as
to-be-skipped in further compactions, in order to improve efficiency.  One
of the reasons to fail isolating pages is that isolation is not attempted
in pageblocks that are not of MIGRATE_MOVABLE (or CMA) type.

The problem is that blocks skipped due to not being MIGRATE_MOVABLE in
async compaction become skipped due to the temporary mark also in future
sync compaction.  Moreover, this may follow quite soon during
__alloc_page_slowpath, without much time for kswapd to clear the pageblock
skip marks.  This goes against the idea that sync compaction should try to
scan these blocks more thoroughly than the async compaction.

The fix is to ensure in async compaction that these !MIGRATE_MOVABLE
blocks are not marked to be skipped.  Note this should not affect
performance or locking impact of further async compactions, as skipping a
block due to being !MIGRATE_MOVABLE is done soon after skipping a block
marked to be skipped, both without locking.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>