-M, --total_memory=NUM[B|K|M|G] Amount of memory on a system for memory utilization calculations above. If itdoesnotendwith K,M,G thenits assumed to be B (bytes)
同时设定阈值需要使用 -m 参数，即：
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-m, --memory_utilization=[WARN,CRIT] This calculates percent of total memory on system used by redis, which is utilization=redis_memory_rss/total_memory*100. Total_memory on server must be specified with -M since Redis doesnot report itand can use maximum memory unless you enabled virtual memory andset a limit (I plan to test this case and see ifit gets reported then). If you specify -m by itself, the plugin will just output this info, with '-f' it will also include this in performance data. You can also specify parameter values which are interpreted as WARNING and CRITICAL thresholds.