long getGlobalMemStoreLimitLowMark() {
    return this.globalMemStoreLimitLowMark;
  }
RegionServerAccounting keeps record of some basic real time information about the Region Server.
Currently, it keeps record the global memstore size and global memstore on-heap and off-heap
overhead. It also tracks the replay edits per region.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RegionServerAccounting.java