Re: [PATCH 10/27] mm, vmscan: Clear congestion, dirty and need for compaction on a per-node basis

[Vlastimil Babka]

On 06/09/2016 08:04 PM, Mel Gorman wrote:
Congested and dirty tracking of a node and whether reclaim should stall
is still based on zone activity. This patch considers whether the kernel
should stall based on node-based reclaim activity.

I'm a bit confused about the description vs actual code.
It appears to move some duplicated code to a related function, which is 
fine. The rest of callsites that didn't perform the clearing before 
(prepare_kswapd_sleep() and wakeup_kswapd()) might be a bit overkill, 
but won't hurt. But I don't see the part "considers whether the kernel
should stall based on node-based reclaim activity". Is something missing?

Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
---
 mm/vmscan.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index dd68e3154732..e4f3e068b7a0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2966,7 +2966,17 @@ 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;
 }

 /*
@@ -3112,13 +3122,6 @@ 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);
                        }
                }

@@ -3177,11 +3180,8 @@ 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;
-                       }
                }

                /*