Re: [Bigsister-general] Memory Usage Issue

[Matt Kettler <suppressed>]

Linda Hu wrote:
> Hi,
>  
> I found that  Memory Usage can only shows the usage of "Swap" or
> "Virtual Memory". Is any possible I can monitor Physical Memory in servers?
>  

Why would you want to monitor Physical Memory? If your OS is working properly,
Physical Memory should always be nearly 100% used, with only enough free to be
able to do high-priority driver allocations without blocking.

If not used by applications, the disk caching should expand to fill the rest,
and get re-allocated to apps when needed.

I personally find the best statistics to be:
	total VM
	swap in-use
	cache/buffer size


Take for example one of my servers with 512m of physical ram:

             total       used       free     shared    buffers     cached
Mem:        514556     499728      14828          0     164428     148296
-/+ buffers/cache:     187004     327552
Swap:      2104432        128    2104304


Note that physical memory only has 14.8M free, but there's 148.2M of cache and
164M of i/o buffering.

Only 128k of the Swap is being used, and given there's so much cache that 128k
is likely to be pages that have not been used for a very long time (ie: unused
for days). So the kernel decided they are pages that aren't going to be used on
any regular basis (error traps, code not used by my config, etc), thus it
swapped them out to make room for more disk cache.







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