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: f20ad70ca336 ("mm, compaction: move pageblock checks up from isolate_migratepages_range()")
[vbabka@suse.cz: expanded the changelog]
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index ccf97b02b85f32d38f6f68a41bedf89b9a1ee596..4a0d4b8ccde8a60c502200f7eeb8a2f521382ef1 100644 (file)
--- a/mm/compaction.c
+++ b/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;