On Wed, Feb 19, 2020 at 12:42:20PM -0800, Sultan Alsawaf wrote:
> > Again, do you have more details about the workload and what was the
> > cause of responsiveness issues? Because I would expect that the
> > situation would be quite opposite because it is usually the direct
> > reclaim that is a source of stalls visible from userspace. Or is this
> > about a single CPU situation where kswapd saturates the single CPU and
> > all other tasks are just not getting enough CPU cycles?
>
> The workload was having lots of applications open at once. At a certain point
> when memory ran low, my system became sluggish and kswapd CPU usage skyrocketed.
> I added printks into kswapd with this patch, and my premature exit in kswapd
> kicked in quite often.
>
This could be watermark boosting run wild again. Can you test with
sysctl vm.watermark_boost_factor=0 or the following patch? (preferably
both to compare and contrast).
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 572fb17c6273..71dd47172cef 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3462,6 +3462,25 @@ static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
return false;
}
+static void acct_boosted_reclaim(pg_data_t *pgdat, int classzone_idx,
+ unsigned long *zone_boosts)
+{
+ struct zone *zone;
+ unsigned long flags;
+ int i;
+
+ for (i = 0; i <= classzone_idx; i++) {
+ if (!zone_boosts[i])
+ continue;
+
+ /* Increments are under the zone lock */
+ zone = pgdat->node_zones + i;
+ spin_lock_irqsave(&zone->lock, flags);
+ zone->watermark_boost -= min(zone->watermark_boost, zone_boosts[i]);
+ spin_unlock_irqrestore(&zone->lock, flags);
+ }
+}
+
/* Clear pgdat state for congested, dirty or under writeback. */
static void clear_pgdat_congested(pg_data_t *pgdat)
{
@@ -3654,9 +3673,17 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
if (!nr_boost_reclaim && balanced)
goto out;
- /* Limit the priority of boosting to avoid reclaim writeback */
- if (nr_boost_reclaim && sc.priority == DEF_PRIORITY - 2)
- raise_priority = false;
+ /*
+ * Abort boosting if reclaiming at higher priority is not
+ * working to avoid excessive reclaim due to lower zones
+ * being boosted.
+ */
+ if (nr_boost_reclaim && sc.priority == DEF_PRIORITY - 2) {
+ acct_boosted_reclaim(pgdat, classzone_idx, zone_boosts);
+ boosted = false;
+ nr_boost_reclaim = 0;
+ goto restart;
+ }
/*
* Do not writeback or swap pages for boosted reclaim. The
@@ -3738,18 +3765,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
out:
/* If reclaim was boosted, account for the reclaim done in this pass */
if (boosted) {
- unsigned long flags;
-
- for (i = 0; i <= classzone_idx; i++) {
- if (!zone_boosts[i])
- continue;
-
- /* Increments are under the zone lock */
- zone = pgdat->node_zones + i;
- spin_lock_irqsave(&zone->lock, flags);
- zone->watermark_boost -= min(zone->watermark_boost, zone_boosts[i]);
- spin_unlock_irqrestore(&zone->lock, flags);
- }
+ acct_boosted_reclaim(pgdat, classzone_idx, zone_boosts);
/*
* As there is now likely space, wakeup kcompact to defragment
