Switching Fedora to pae kernel by default?

[Avi Kivity]

Jeremy Katz wrote:
> On Monday, January 19 2009, Avi Kivity said:
>   
>> Jeremy Katz wrote:
>>     
>>> That said, we currently do install the PAE kernel if you have 4 GB+ of
>>> RAM[1].  Switching to it by default is problematic because then we're
>>> back to using different kernels for different cases 
>>>       
>> You have that now, don't you?  One case for <4GB and one for >=4GB.   
>> Worse, if you install more memory, the kernel doesn't see it.
>>
>> Downgrading your CPU to one which does not support PAE should be rare.
>>     
>
> Yes, but at least the "running a different kernel" case is currently the
> relatively rare one.
>   

It will become more and more frequent as machines get beefier.  If we 
switch to PAE, it will be the non-PAE case which is rare.

btw, what's wrong with running a different kernel?  So long as the 
configs match, there shouldn't be a difference in reliability.


>>> and it also makes
>>> the 'what do you with the live image' case a lot more complex.
>>>       
>> I'd just go with PAE here.
>>     
>
> Can't do so -- the live image is definitely used on a lot of hardware
> that isn't PAE capable.  Many/most Pentium M's didn't support it, the OLPC 
> doesn't[1].  And those are common hardware targets for the live image
>   

So either put both kernels there, or the non-PAE kernel.

>>> The _real_ fix here is to get PAE runtime much like was finally done
>>> with SMP :-)
>>>       
>> Patches, as they say, are welcome.  
>>     
>
> Low-level x86 setup code isn't quite my forte...  Hence I go for
> goading others into doing it ;-)
>   

I meant, "this requires a monumental amount of work".

>   
>> But you could install both kernels  
>> and have the bootloaded choose (sticks wax balls into ears).
>>     
>
> Want to write code for syslinux and grub to do the auto-choosing?  

Not really.  I don't see it as particularly difficult.

With grub, you could use multiboot to add a module to select the correct 
kernel, maybe.

I think Windows works this way, with the /PAE switch on the kernel 
command line causing a different kernel to be loaded.

> Then
> we also have to figure out a way to shoe-horn another 50 MB of stuff
> into the already full live image

Cut away the drivers for Infiniband and similarly useless hardware (for 
livecds, that is).  Put them in a separate subpackage or use 
steam-powered rm -rf.

-- 
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