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Title
The Memory Utilization rule on Linux doesn't seem to account for disk caching. -
Description
In Linux there is a feature called Disk caching, if the Disk Cache is high and the memory is high both elements should be taken into account as part of Memory utilization metric and on Memory Utilization rule. -
Resolution
The logic in "Memory Utilization" rule is simple, just compare the value of memory utilization with an expected value, then check whether it's required to raise an alarm. Actually disk caching is taken into account of memory utilization. In IC(Infrastructure), disk caching is considered as a part of free memory, regarding calculate memory utilization. Let's see below statements:
1. For below output mentioned in Linux Web Site 1, here free memory = free + buffers + cached, while used memory is 635, so memory utilization is 635/1504 or (1504 - free
memory[13 + 91 + 764])/1504 so we can think that disk caching is taken into account of memory utilization.
$ free -mtotal used free shared buffers cachedMem: 1504 1491 13 0 91 764-/+ buffers/cache: 635 869Swap: 2047 6 2041The author explained again that if you don't know how to read the numbers, you'll think your RAM is 99% full when it's really just 42%!2. See item #1 and #2 in below link. The second line tells that 4.6 GB is free. This is the free memory in first line added with the buffers and cached amount of memory.Since the concern is that disk caching should be considered as a part of used memory, if so, then memory utilization in the example mentioned in item #1 is 99% while the proper value is 42%. Per this, then IC works as expected.