PAE versus HIGHMEM64

[Chris Lalancette]

Thorsten Leemhuis wrote:
> 
> Which brings me to the point why I'm writing this mail: should we enable
> PAE by default after F8 is out and ship a HIGHMEM64G-Kernel instead on
> x86-32? Then normal users on x86-32 can benefit from NX by default. Or
> is that considered "not worth the trouble because we ship execshield
> already"?
> 
> Further: Does PAE-by-default still make lots of machines unbootable (I
> doubt that for newer machines, as some-well-known-other-os enables PAE
> since its service pack 2 by default iirc)? If we suspect it still does:
> could we fix that by some kind of automatic "if machine is newer than
> ${year}" check in the kernel?
> 
> Just wondering.

Yes, it does still tend to break machines, especially laptops and older 
machines (we run into this a lot with Xen, since we only ship a PAE 
variant there).  Unfortunately, PAE is a compile time option, not 
something that can (currently) be turned on or off at runtime.  It would 
be nice to make it a runtime option (IIRC, OpenSolaris does this), but I 
don't know if it is worth the effort given that 32-bit should be 
becoming less and less common.

Chris Lalancette