mm, cma: prevent nr_isolated_* counters from going negative

/proc/sys/vm/stat_refresh warns nr_isolated_anon and nr_isolated_file go
increasingly negative under compaction: which would add delay when
should be none, or no delay when should delay.  The bug in compaction
was due to a recent mmotm patch, but much older instance of the bug was
also noticed in isolate_migratepages_range() which is used for CMA and
gigantic hugepage allocations.

The bug is caused by putback_movable_pages() in an error path
decrementing the isolated counters without them being previously
incremented by acct_isolated().  Fix isolate_migratepages_range() by
removing the error-path putback, thus reaching acct_isolated() with
migratepages still isolated, and leaving putback to caller like most
other places do.

Fixes: edc2ca6 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")
[[email protected]: expanded the changelog]
Signed-off-by: Hugh Dickins <[email protected]>
Signed-off-by: Vlastimil Babka <[email protected]>
Acked-by: Joonsoo Kim <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/compaction.c

@@ -852,16 +852,8 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
 		pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
 							ISOLATE_UNEVICTABLE);
 
-		/*
-		 * In case of fatal failure, release everything that might
-		 * have been isolated in the previous iteration, and signal
-		 * the failure back to caller.
-		 */
-		if (!pfn) {
-			putback_movable_pages(&cc->migratepages);
-			cc->nr_migratepages = 0;
+		if (!pfn)
 			break;
-		}
 
 		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
 			break;