Due to vmstat counters percpu drift result of too_many_isolated() check
can be false-positive. Unfortunately it can be stable false-positive:
for example if zone at the one moment hasn't active/inactive pages at all
(for small zones like "DMA" this is very likely) but its atomic part of
isolated-pages counter is non-zero. In this sutuation shrink_inactive_list()
and isolate_migratepages() will loop forever around too_many_isolated().
After this patch too_many_isolated() will sum percpu fractions of
isolated pages counter if atomic part above watermark, but not higher than
watermark plus possible percpu drift.
We can ignore drift for active/inactive pages counters, because sooner or later
isolate pages counter drops to zero.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
---
mm/compaction.c | 11 +++++++++--
mm/vmscan.c | 5 +++++
2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 899d956..2d6fced 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -231,7 +231,7 @@ static void acct_isolated(struct zone *zone, struct compact_control *cc)
/* Similar to reclaim, but different enough that they don't share logic */
static bool too_many_isolated(struct zone *zone)
{
- unsigned long active, inactive, isolated;
+ unsigned long active, inactive, isolated, watermark;
inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
zone_page_state(zone, NR_INACTIVE_ANON);
@@ -240,7 +240,14 @@ static bool too_many_isolated(struct zone *zone)
isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
zone_page_state(zone, NR_ISOLATED_ANON);
- return isolated > (inactive + active) / 2;
+ watermark = (inactive + active) / 2;
+
+ if (isolated > watermark &&
+ isolated - watermark <= zone->percpu_drift * 2)
+ isolated = zone_page_state_snapshot(zone, NR_ISOLATED_FILE) +
+ zone_page_state_snapshot(zone, NR_ISOLATED_ANON);
+
+ return isolated > watermark;
}
/* possible outcome of isolate_migratepages */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 393ebce..3918c5f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1320,6 +1320,11 @@ static int too_many_isolated(struct zone *zone, int file,
isolated = zone_page_state(zone, NR_ISOLATED_ANON);
}
+ if (isolated > inactive &&
+ isolated - inactive <= zone->percpu_drift)
+ isolated = zone_page_state_snapshot(zone,
+ file ? NR_ISOLATED_FILE : NR_ISOLATED_ANON);
+
return isolated > inactive;
}
--
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