DragonFly kernel List (threaded) for 2007-01
DragonFly BSD
DragonFly kernel List (threaded) for 2007-01
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Re: Re vkernel and all

From: "Thomas E. Spanjaard" <tgen@xxxxxxxxxxxxx>
Date: Tue, 23 Jan 2007 18:44:35 +0000

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.

        Thomas E. Spanjaard

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