[Xymon] Improving memory monitoring

[Mark Felder]

On Tue, Apr 14, 2015, at 06:56, Steve Hill wrote:
> 
> 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?
> 

I agree -- this would have been very valuable to me in the past. I'm not
currently aware of a way to do this, but I've recently discovered so
many Xymon features I was unaware of that maybe it's possible...