mm: bail out in shrink_inactive_list()

With node-lru, if there are enough reclaimable pages in highmem but
nothing in lowmem, VM can try to shrink inactive list although the
requested zone is lowmem.

The problem is that if the inactive list is full of highmem pages then a
direct reclaimer searching for a lowmem page waste CPU scanning
uselessly.  It just burns out CPU.  Even, many direct reclaimers are
stalled by too_many_isolated if lots of parallel reclaimer are going on
although there are no reclaimable memory in inactive list.

I tried the experiment 4 times in 32bit 2G 8 CPU KVM machine to get
elapsed time.

	hackbench 500 process 2

 = Old =

  1st: 289s 2nd: 310s 3rd: 112s 4th: 272s

 = Now =

  1st: 31s  2nd: 132s 3rd: 162s 4th: 50s.

[akpm@linux-foundation.org: fixes per Mel]
Link: http://lkml.kernel.org/r/1469433119-1543-1-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0294ab34f4759c20ad696703a67d993055c1d76b..650d26832569a9c41399f3a5da49c6eb56015d46 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1652,6 +1652,30 @@ static int current_may_throttle(void)
                bdi_write_congested(current->backing_dev_info);
 }
 
+static bool inactive_reclaimable_pages(struct lruvec *lruvec,
+                               struct scan_control *sc, enum lru_list lru)
+{
+       int zid;
+       struct zone *zone;
+       int file = is_file_lru(lru);
+       struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+
+       if (!global_reclaim(sc))
+               return true;
+
+       for (zid = sc->reclaim_idx; zid >= 0; zid--) {
+               zone = &pgdat->node_zones[zid];
+               if (!populated_zone(zone))
+                       continue;
+
+               if (zone_page_state_snapshot(zone, NR_ZONE_LRU_BASE +
+                               LRU_FILE * file) >= SWAP_CLUSTER_MAX)
+                       return true;
+       }
+
+       return false;
+}
+
 /*
  * shrink_inactive_list() is a helper for shrink_node().  It returns the number
  * of reclaimed pages
@@ -1674,6 +1698,9 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
        struct pglist_data *pgdat = lruvec_pgdat(lruvec);
        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
 
+       if (!inactive_reclaimable_pages(lruvec, sc, lru))
+               return 0;
+
        while (unlikely(too_many_isolated(pgdat, file, sc))) {
                congestion_wait(BLK_RW_ASYNC, HZ/10);