Re: Re vkernel and all

["Thomas E. Spanjaard" <tgen@xxxxxxxxxxxxx>]

Oliver Fromme wrote:
> When I start a qemu virtual machine with, say, 128 MB of
> RAM, then that memory is allocated to the qemu process in
> a normal way, i.e. it can also be paged to swap.
>
> If I understand you correctly, then DF's virtual kernels
> work differently:  they delegate the allocations to the
> real kernel.  Right?  I guess that means that the memory
> of user processes running in the vkernel can be paged to
> swap, while the pages of the vkernel (its virtual KVM,
> so to speak) are locked to physical RAM, just like the
> real kernel.  Is that correct?

I don't know if the vkernel's vmspace's pages are resident or not.

> What about the cache (VM cache, buffer cache, whatever).
> During normal operation, a kernel tends to use almost all
> free RAM for the cache, i.e. there is almost zero free
> RAM.  Do the virtual kernels behave the same?  Do they
> even have their own caches?

The vkernel does not have a buffer cache like the real kernel, because 
it just acts like a normal userland process to the real kernel in this 
regard.

> I guess what I'm really trying to ask is this:  If I
> start 4 vkernels, each with 256 MB RAM, will they
> use 1 GB of real memory, even if only a few small
> processes run inside them?

I suspect 1GB of real memory will be absorbed by the vkernel, though as 
I said above, I'm not sure.

Cheers,
--
        Thomas E. Spanjaard
        tgen@netphreax.net

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