Correctly determine free memory amount before swapping

["Gregory Giguashvili" <Gregoryg@ParadigmGeo.com>]

I apologize if this question was already discussed here - Google search
revealed lots of similar topics, but none in this particular aspect.

I need to commit the largest chunk of memory in the quickest way. This
operation may be slowed down by swapping - that's why I don't want to
get there.

Assuming that I define "free memory" as maximum memory that can be
allocated without causing swapping, is there a way I can give a rough
"free memory" amount estimate? I've tried to play with /proc/meminfo
values with some progress, but I'd like to get a qualified answer from
people working with MM.

According to my humble experiments with 2.4 and 2.6 kernels, some cashed
memory reported in /proc/meminfo is reused and some is swapped. The real
problem here is that I not sure what the right way is to "predict" how
much cached memory will be discarded before starting to swap when system
is low on available RAM.

In 2.4 kernels, I was using the following formula (/proc/meminfo names):
free = MemFree + (Inact_dirty > Inact_target ? Inact_dirty -
Inact_target : 0)

In 2.6 kernels, I'm still working on it.

I understand that this is a complicated question, but I'm looking for a
rough simplification of this matter that would work in most of the cases
with little or no swapping.

Any suggestions are greatly appreciated. 

Thanks a lot
Giga
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