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

From: Oliver Fromme <check+jcc1g100rss0n5wu@xxxxxxxxxx>
Date: 23 Jan 2007 18:04:57 GMT

Matthew Dillon wrote:
 >    A virtualized kernel requires actually reserving the (memory) resources 
 >    beforehand, and it also guarentees that there won't be any resource
 >    leakage or starvation.  If you give a vkernel 64 MB of ram, that's all
 >    it will use, period.

A few (dumb) questions, just out of curiosity ...

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?

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?

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?

Unfortunately I currently don't have a spare machine to
install -preview and play with vkernels myself.  :-(

Best regards

Oliver Fromme,  secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd

Any opinions expressed in this message may be personal to the author
and may not necessarily reflect the opinions of secnetix in any way.

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