Re: [uml-devel] [PATCH] Locking user-mode kernel RAM into host physical RAM

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

Alle 20:01, lunedì 8 dicembre 2003, Jeff Dike ha scritto:
> As far as I'm concerned, this is papering over the symptoms rather than
> fixing a real problem.
>
> If you're really not overselling memory, then the host should not be
> swapping. If it is, then that's the problem.
>
> > My experience with 2.4 as  a host kernel is that it will quite happily
> > swap out pages from running  applications to use as disc cache; this
> > is apparently alleviated with 2.6's  "swappiness" kernel parameter.
>
> This being the case, you should maybe be looking at 2.6 as your host.
>
> > I hope that it's obvious enough to warrant inclusion in the next
> > release of  the UML patch
>
> It's not.  Feel free to argue, but this is really the wrong thing to do,
> IMHO.
But anyway, if the "physical memory" of the guest is not guaranted to be 
actually physical, then the UML's kernel VM will get fooled. What's more, 
it's the guest's VM which must decide what has to be swapped.
The only swap that must be used is the UML's one. He must be fair to his 
customer(i.e. no overselling), but done that the host can't swap anything 
out.

> /dev/anon is a new host driver which implements the munmap semantics needed
> by UML physical memory (pages are release to the host when they're no
> longer mapped, even if they're dirty).
It means that the guest VM will see that the available memory has shrinked and 
that it will swap things out following the new memory limit? It seems to me a 
little bit difficult. This (if I understand correctly) requires core VM 
changes(the stock VM isn't much tested with shrinking/increasing memory 
sizes, if this is supported at all, for strange architectures).

-- 
cat <<EOSIGN
Paolo Giarrusso, aka Blaisorblade
Linux Kernel 2.4.21/2.6.0-test on an i686; Linux registered user n. 292729
EOSIGN



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