Re: Sigma0 and L4 Core

On Fri, Mar 15, 2013 at 1:16 AM, Taylor Bioniks <[email protected]> wrote:
> I know that sigma0 is the memory manager and pager.
> I would like to know if the server sigma0 could be merged into the core
> kernel?
> Or would doing this cause L4 to lose a lot of it's speed and stability?
> The reason I ask this is because I read that L4's IPC was designed to stay
> in the CPU cache, and I think making the kernel bigger would make this no
> longer possible.

I may be wrong, but this is how I understand the rationale behind
a user-space sigma0:

Basically, sigma0 is only needed at boot time to hand out
FPages to the pagers of the OS personality/personalities
running on top of L4. Once that happens, all paging activities will
be handled by those OS-specific pagers. There's no reason to keep
sigma0 in kernel space anymore at this point... especially since
pages that have once been granted/mapped by sigma0 to some
other tasks (including those OS-specific pagers) are gone forever.
Remember: sigma0 isn't a full-fledged pager that takes FPages
back once they're not needed by the tasks anymore. It's just some
kind of "bootstrapping pager."

-cpghost.

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