From d4b752081863b2f2f224b1e2042f1bb8a080a05f Mon Sep 17 00:00:00 2001
From: Henning Baldersheim <balder@oath.com>
Date: Wed, 5 Sep 2018 11:03:19 +0200
Subject: If memory utilisation is not found to be stable, return the median
 sample.

---
 .../process_memory_stats_test.cpp                     |  8 ++++++++
 .../src/vespa/vespalib/util/process_memory_stats.cpp  | 19 +++++++++++--------
 .../src/vespa/vespalib/util/process_memory_stats.h    |  2 ++
 3 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/staging_vespalib/src/tests/util/process_memory_stats/process_memory_stats_test.cpp b/staging_vespalib/src/tests/util/process_memory_stats/process_memory_stats_test.cpp
index 45e75547fb2..26444fa8606 100644
--- a/staging_vespalib/src/tests/util/process_memory_stats/process_memory_stats_test.cpp
+++ b/staging_vespalib/src/tests/util/process_memory_stats/process_memory_stats_test.cpp
@@ -80,4 +80,12 @@ TEST("grow mapped memory")
     munmap(mapAddr, mapLen);
 }
 
+TEST("order samples")
+{
+    ProcessMemoryStats a(0,7,0,0,0);
+    ProcessMemoryStats b(0,8,0,0,0);
+    EXPECT_TRUE(a < b);
+    EXPECT_FALSE(b < a);
+}
+
 TEST_MAIN() { TEST_RUN_ALL(); }
diff --git a/staging_vespalib/src/vespa/vespalib/util/process_memory_stats.cpp b/staging_vespalib/src/vespa/vespalib/util/process_memory_stats.cpp
index 138e7a25803..f0cbefd443b 100644
--- a/staging_vespalib/src/vespa/vespalib/util/process_memory_stats.cpp
+++ b/staging_vespalib/src/vespa/vespalib/util/process_memory_stats.cpp
@@ -4,6 +4,7 @@
 #include <vespa/vespalib/stllike/asciistream.h>
 #include <fstream>
 #include <sstream>
+#include <algorithm>
 
 #include <vespa/log/log.h>
 
@@ -182,18 +183,20 @@ ProcessMemoryStats::toString() const
 ProcessMemoryStats
 ProcessMemoryStats::create(uint64_t sizeEpsilon)
 {
-    ProcessMemoryStats prevStats = createStatsFromSmaps();
-    const size_t NUM_TRIES = 10;
+    constexpr size_t NUM_TRIES = 10;
+    std::vector<ProcessMemoryStats> samples;
+    samples.reserve(NUM_TRIES);
+    samples.push_back(createStatsFromSmaps());
     for (size_t i = 0; i < NUM_TRIES; ++i) {
-        ProcessMemoryStats currStats = createStatsFromSmaps();
-        if (prevStats.similarTo(currStats, sizeEpsilon)) {
-            return prevStats;
+        samples.push_back(createStatsFromSmaps());
+        if (samples.back().similarTo(*(samples.rbegin()+1), sizeEpsilon)) {
+            return samples.back();
         }
         LOG(info, "create(): Memory stats have changed, trying to read smaps file again: i=%zu, prevStats={%s}, currStats={%s}",
-            i, prevStats.toString().c_str(), currStats.toString().c_str());
-        prevStats = currStats;
+            i, (samples.rbegin()+1)->toString().c_str(), samples.back().toString().c_str());
     }
-    return prevStats;
+    std::sort(samples.begin(), samples.end());
+    return samples[samples.size()/2];
 }
 
 }
diff --git a/staging_vespalib/src/vespa/vespalib/util/process_memory_stats.h b/staging_vespalib/src/vespa/vespalib/util/process_memory_stats.h
index fe5062f75cd..44c7c378623 100644
--- a/staging_vespalib/src/vespa/vespalib/util/process_memory_stats.h
+++ b/staging_vespalib/src/vespa/vespalib/util/process_memory_stats.h
@@ -4,6 +4,7 @@
 
 #include <cstdint>
 #include <vespa/vespalib/stllike/string.h>
+#include <vector>
 
 namespace vespalib {
 
@@ -37,6 +38,7 @@ public:
     uint64_t getMappingsCount() const { return _mappings_count; }
     bool similarTo(const ProcessMemoryStats &rhs, uint64_t sizeEpsilon) const;
     vespalib::string toString() const;
+    bool operator < (const ProcessMemoryStats & rhs) const { return _mapped_rss < rhs._mapped_rss; }
 
     /** for unit tests only */
     ProcessMemoryStats(uint64_t, uint64_t, uint64_t, uint64_t, uint64_t);
-- 
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