On Tue, Apr 23, 2002 at 09:44:50AM -0300, "Marc G. Fournier"

> Next, again, if I'm reading this right ... if I set my KVA to 3G,
> when the system boots, it will reserve 3G of *physical* RAM for
> the kernel itself, correct?  So on a 4G machine, 1G of *physical*
> RAM will be available for UVAs ... so, if I run >1G worth of
> processes, that is where swapping to disk comes in, right?  Other
> then the massive performance hit, and the limit you mention about
> some parts of UVA not being swappable, I could theoretically have
> >4G of swap to page out to?

You can have up to ~12GB of usable swap space, as I've heard. Don't
remember why such arbitrary limit, unfortunately. Information about
such topics is spread over several lists arhives, usually the
subjects are strange, too.. so hard to find out. As I understand it
you are on the track, having 3GB allocated to KVA means 1GB for UVA,
whatever it exactly means. Userspace processes will allocate memory
from UVA space and can grow over 1GB of size if needed by swapping.
You can certainly have more than one over-1GB process going on at
the same time, but swapping will constrain your performance.
I'm sure Terry or some other knowledgeable person will correct me if
it doesn't make sense.

> Is there a reason why this stuff isn't auto-scaled based on RAM as
> it is?

Probably lack of manpower, to code it up you'll have to understand
every bit of it, but as we currently see, we don't understand it,
probably many others as well :-)

Vallo Kallaste

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