[Xymon] Improving memory monitoring

[Steve Hill]

I'm working on improving my Xymon configuration to reduce the number of 
false alerts that we get.  In particular, memory monitoring is a bit of 
a problem so I'm hoping someone will be able to offer some advice.

At the moment, Xymon is set up with something like:

MEMPHYS 100 101
MEMSWAP 20 40
MEMACT 95 97

I pretty much don't care about MEMPHYS.  The problem with MEMSWAP and 
MEMACT is that they work independently or each other - i.e. the above 
will give me an alert if > 97% of the RAM is used OR > 40% of swap is used.

However, this results in warnings for systems that have a lot of idle 
data in memory.  The Linux kernel will page out idle data (increasing 
swap usage and reducing RAM usage) and use that space for 
buffers/caches, and this is a very sensible strategy.  Unfortunately, 
then Xymon comes along and notices that there's lots of swap in use and 
throws an alert, even though there's plenty of RAM free.

Basically, I don't care that a machine is 4GB into swap if it has 5GB of 
free ram - that isn't a problem, it just means there's quite a lot of 
idle data that the kernel has decided can be paged out.  I do care if 
it's 4GB into swap and only has 0.5GB of free RAM since this would 
indicate that it's actually short of memory.

What I really need is to warn if > x% of the RAM is used AND > y% of 
swap is used - is there a way to do that?

Thanks.

-- 
  - Steve Hill
    Technical Director
    Opendium Limited     http://www.opendium.com

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