export memory events high and max metrics

Summary:
Same as D93677082, these are another metrics I want to add to monitor about whether we are close to OOM, and do some test see if we can use them as extra metrics for memory shedding.

The [metrics](https://facebookmicrosites.github.io/cgroup2/docs/memory-controller.html) added are:

- **memory events high**: The number of times processes of the cgroup are throttled and routed to perform direct memory reclaim because the high memory boundary was exceeded.

- **memory events max**: The number of times the cgroup's memory usage was about to go over the max boundary -- if we see failure about reclaim after this happen, we will OOM.

For now memory.high = memory.max in Revproxy settings thus memory_events.high = memory_events.max, but we might change that for better OOM protection so I'm still going to export two metrics here.

Differential Revision: D93800675

fbshipit-source-id: eb050bff5a404d11f574694f7b0bb892667e50a2

Author: Rongxin Xia

proxygen/lib/stats/ResourceData.h

@@ -168,6 +168,14 @@ struct ResourceData : public PeriodicStatsDataBase {
     return memPressureSomeAvg300Pct_;
   }
 
+  [[nodiscard]] int64_t getMemEventsHighCount() const {
+    return memEventsHighCount_;
+  }
+
+  [[nodiscard]] int64_t getMemEventsMaxCount() const {
+    return memEventsMaxCount_;
+  }
+
   [[nodiscard]] double getCpuPressureAvg10Pct() const {
     return cpuPressureAvg10Pct_;
   }
@@ -367,6 +375,11 @@ struct ResourceData : public PeriodicStatsDataBase {
     memPressureSomeAvg300Pct_ = avg300;
   }
 
+  void setMemEventsStats(int64_t highCount, int64_t maxCount) {
+    memEventsHighCount_ = highCount;
+    memEventsMaxCount_ = maxCount;
+  }
+
   void setIoPressureStats(double avg10, double avg60, double avg300) {
     ioPressureAvg10Pct_ = avg10;
     ioPressureAvg60Pct_ = avg60;
@@ -439,6 +452,9 @@ struct ResourceData : public PeriodicStatsDataBase {
   double memPressureSomeAvg60Pct_{0};
   double memPressureSomeAvg300Pct_{0};
 
+  int64_t memEventsHighCount_{0};
+  int64_t memEventsMaxCount_{0};
+
   double ioPressureAvg10Pct_{0};
   double ioPressureAvg60Pct_{0};
   double ioPressureAvg300Pct_{0};