mm/compaction: stop isolation if too many pages are isolated and we h…

…ave pages to migrate

In isolate_migratepages_block, if we have too many isolated pages and
nr_migratepages is not zero, we should try to migrate what we have
without wasting time on isolating.

In theory it's possible that multiple parallel compactions will cause
too_many_isolated() to become true even if each has isolated less than
COMPACT_CLUSTER_MAX, and loop forever in the while loop.  Bailing
immediately prevents that.

[[email protected]: changelog addition]

Fixes: 1da2f32 (“mm,thp,compaction,cma: allow THP migration for CMA allocations”)
Suggested-by: Vlastimil Babka <[email protected]>
Signed-off-by: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Yang Shi <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

mm/compaction.c

@@ -817,6 +817,10 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 	 * delay for some time until fewer pages are isolated
 	 */
 	while (unlikely(too_many_isolated(pgdat))) {
+		/* stop isolation if there are still pages not migrated */
+		if (cc->nr_migratepages)
+			return 0;
+
 		/* async migration should just abort */
 		if (cc->mode == MIGRATE_ASYNC)
 			return 0;