[PATCH] mm: prevent NR_ISOLATE_* stats from going negative

[Rabin Vincent]

From: Rabin Vincent <rabinv@xxxxxxxx>

Commit 6afcf8ef0ca0 ("mm, compaction: fix NR_ISOLATED_* stats for pfn
based migration") moved the dec_node_page_state() call (along with the
page_is_file_cache() call) to after putback_lru_page().  But
page_is_file_cache() can change after putback_lru_page() is called, so
it should be called before putback_lru_page(), as it was before that
patch, to prevent NR_ISOLATE_* stats from going negative.

Without this fix, non-CONFIG_SMP kernels end up hanging in the
while(too_many_isolated()) { congestion_wait() } loop in
shrink_active_list() due to the negative stats.

 Mem-Info:
  active_anon:32567 inactive_anon:121 isolated_anon:1
  active_file:6066 inactive_file:6639 isolated_file:4294967295
                                                    ^^^^^^^^^^
  unevictable:0 dirty:115 writeback:0 unstable:0
  slab_reclaimable:2086 slab_unreclaimable:3167
  mapped:3398 shmem:18366 pagetables:1145 bounce:0
  free:1798 free_pcp:13 free_cma:0

Fixes: 6afcf8ef0ca0 ("mm, compaction: fix NR_ISOLATED_* stats for pfn based migration")
Cc: Ming Ling <ming.ling@xxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Rabin Vincent <rabinv@xxxxxxxx>
---
 mm/migrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index ed97c2c..738f1d5 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -184,9 +184,9 @@ void putback_movable_pages(struct list_head *l)
 			unlock_page(page);
 			put_page(page);
 		} else {
-			putback_lru_page(page);
 			dec_node_page_state(page, NR_ISOLATED_ANON +
 					page_is_file_cache(page));
+			putback_lru_page(page);
 		}
 	}
 }
-- 
2.7.0