Re: [PATCH 11/34] mm, vmscan: remove duplicate logic clearing node congestion and dirty state

[Vlastimil Babka]

On 07/08/2016 11:34 AM, Mel Gorman wrote:
Reclaim may stall if there is too much dirty or congested data on a node.
This was previously based on zone flags and the logic for clearing the
flags is in two places.  As congestion/dirty tracking is now tracked on a
per-node basis, we can remove some duplicate logic.
Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
Acked-by: Hillf Danton <hillf...@alibaba-inc.com>

I don't think it's that big a side-effect to be concerned. I would be 
more worried about frequently dirtying cache lines from other 
zone_balanced callers where, but I guess even the calls from 
wakeup_kswapd() rarely return true for zone_balanced(), otherwise the 
wakeups wouldn't have a reason to happen.

Acked-by: Vlastimil Babka <vba...@suse.cz>

---
 mm/vmscan.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 01fe4708e404..8b39b903bd14 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3008,7 +3008,17 @@ static bool zone_balanced(struct zone *zone, int order, 
int classzone_idx)
 {
        unsigned long mark = high_wmark_pages(zone);

-       return zone_watermark_ok_safe(zone, order, mark, classzone_idx);
+       if (!zone_watermark_ok_safe(zone, order, mark, classzone_idx))
+               return false;
+
+       /*
+        * If any eligible zone is balanced then the node is not considered
+        * to be congested or dirty
+        */
+       clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags);
+       clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags);
+
+       return true;
 }

 /*
@@ -3154,13 +3164,6 @@ static int balance_pgdat(pg_data_t *pgdat, int order, 
int classzone_idx)
                        if (!zone_balanced(zone, order, 0)) {
                                classzone_idx = i;
                                break;
-                       } else {
-                               /*
-                                * If any eligible zone is balanced then the
-                                * node is not considered congested or dirty.
-                                */
-                               clear_bit(PGDAT_CONGESTED, 
&zone->zone_pgdat->flags);
-                               clear_bit(PGDAT_DIRTY, 
&zone->zone_pgdat->flags);
                        }
                }

@@ -3219,11 +3222,8 @@ static int balance_pgdat(pg_data_t *pgdat, int order, 
int classzone_idx)
                        if (!populated_zone(zone))
                                continue;

-                       if (zone_balanced(zone, sc.order, classzone_idx)) {
-                               clear_bit(PGDAT_CONGESTED, &pgdat->flags);
-                               clear_bit(PGDAT_DIRTY, &pgdat->flags);
+                       if (zone_balanced(zone, sc.order, classzone_idx))
                                goto out;
-                       }
                }

                /*