Re: loadavg and memusage display during init

[Martin Pala]

My first though was the same, however i changed my mind :)

Monit on linux displays used memory without buffer cache, the formula is:

  "memory_used = MemTotal - MemFree - Buffers - Cached"

The reason is, that the system will use usualy as much free memory as 
possible for buffers/cache. This will lead to almost 100% memory usage 
each time, even though applications in reality need just subset of this 
amount.

In this context it is not so important to know how large the 
buffers/cache is, but rather the hit ratio of the cache. When the hit 
ratio is low (for example <90%), it could be usefull to add additional 
memory.

Similarly, when you know some absolute value which you preffer for 
buffers/cache, it should be sufficient to watch just real memory usage 
as monit does already (the rest is available for cache, i.e. high memory 
usage means low space for buffer cache).

We plann to add cache hit ratio monitoring support, but it has low 
priority currently on our todo list. Btw. the code will be highly system 
dependent (there are several types of caches and interfaces).

However, when there will be good reason, i think it shouldn't be problem 
to add buffers/cache real size monitoring - let's discusse :)

Martin

John Barton wrote:
...
> A question though:
> monit reports on my system that I am using about 55M of RAM. 'free'
> reports I am using about 71M. It seems that monit is displaying memory
> used after subtracting the memory used for cache, so it is not displaying
> the amount truly in use at the time. I personally would rather see the
> buffer included in the used memory, for a more accurate picture of how
> much free memory I have. You thoughts?
> Thanks,
> -John