PAE versus HIGHMEM64

[Thorsten Leemhuis]

On 15.09.2007 18:27, fedorawiki-noreply at fedoraproject.org wrote:
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> The following page has been changed by PaulFrields: 
> http://fedoraproject.org/wiki/Docs/Beats/Kernel?action=diff&rev2=112&rev1=111
>  [...] 
> +  * The kernel-PAE, for use in 32-bit x86 systems with more
> than 4GB of RAM, or with CPUs that have a NX (No eXecute) feature.
> This kernel support both uniprocessor and multi-processor systems.
> Configured sources are available in the `kernel-PAE-devel` package.

This reminded me of:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=c673f1a9d994de501b674b2bb6a48bd5e912afe0

Quoting Patch description:

> i386: divorce CONFIG_X86_PAE from CONFIG_HIGHMEM64G
> 
> PAE is useful for more than supporting more than 4GB RAM.  It supports
> expanded swapspace and NX executable protections.  Some users may want NX
> or expanded swapspace support without the overhead or instability of
> highmem.  For these reasons, the following patch divorces CONFIG_X86_PAE
> from CONFIG_HIGHMEM64G.

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.

CU
knurd