code: public long getMemoryForMapTask() {
      long value = getDeprecatedMemoryValue();
      if (value == DISABLED_MEMORY_LIMIT) {
        value = normalizeMemoryConfigValue(
                  getLong(JobConf.MAPRED_JOB_MAP_MEMORY_MB_PROPERTY,
                            DISABLED_MEMORY_LIMIT));
      }
      return value;
    }
docs: Get memory required to run a map task of the job, in MB.
  
  If a value is specified in the configuration, it is returned.
  Else, it returns {@link #DISABLED_MEMORY_LIMIT}.
  <p/>
  For backward compatibility, if the job configuration sets the
  key {@link #MAPRED_TASK_MAXVMEM_PROPERTY} to a value different
  from {@link #DISABLED_MEMORY_LIMIT}, that value will be used
  after converting it from bytes to MB.
  @return memory required to run a map task of the job, in MB,
  or {@link #DISABLED_MEMORY_LIMIT} if unset.