Make LoadMetric memory usage calculation constant time

No point in looping over elements. As a bonus, memory usage calculation
is now more accurate as well.

2 files changed, 5 insertions, 7 deletions

diff --git a/metrics/src/vespa/metrics/loadmetric.h b/metrics/src/vespa/metrics/loadmetric.h
index e23973d1681..3982e144846 100644
--- a/metrics/src/vespa/metrics/loadmetric.h
+++ b/metrics/src/vespa/metrics/loadmetric.h
@@ -46,7 +46,8 @@ template<typename MetricType>
 class LoadMetric : public MetricSet {
     std::vector<Metric::LP> _ownerList;
     typedef vespalib::LinkedPtr<MetricType> MetricTypeLP;
-    vespalib::hash_map<uint32_t, MetricTypeLP> _metrics;
+    using MetricMap = vespalib::hash_map<uint32_t, MetricTypeLP>;
+    MetricMap _metrics;
     SumMetric<MetricType> _sum;
 
 public:
@@ -90,5 +91,5 @@ public:
     void addMemoryUsage(MemoryConsumption& mc) const override;
 };
 
-} // documentapi
+} // metrics
 
diff --git a/metrics/src/vespa/metrics/loadmetric.hpp b/metrics/src/vespa/metrics/loadmetric.hpp
index ae743e959d1..7e0518d9403 100644
--- a/metrics/src/vespa/metrics/loadmetric.hpp
+++ b/metrics/src/vespa/metrics/loadmetric.hpp
@@ -71,11 +71,8 @@ template<typename MetricType>
 void
 LoadMetric<MetricType>::addMemoryUsage(MemoryConsumption& mc) const {
     ++mc._loadMetricCount;
-    mc._loadMetricMeta += sizeof(Metric::LP) * _ownerList.size();
-    for (const auto & unused : _metrics) {
-        (void) unused;
-        mc._loadMetricMeta += sizeof(uint32_t) + sizeof(MetricTypeLP);
-    }
+    mc._loadMetricMeta += (sizeof(Metric::LP) * _ownerList.capacity())
+                        + (sizeof(typename MetricMap::value_type) * _metrics.capacity());
     _sum.addMemoryUsage(mc);
     mc._loadMetricMeta += sizeof(LoadMetric<MetricType>)
                         - sizeof(MetricSet)