Removing uvm_emap (aka ephemeral mapping interface)?

[Jaromír Doleček <jaromir.dolecek%gmail.com@localhost>]

Hello,

I suggest to remove emap code.

Unfortunately it turned out as too tricky to implement and use
correctly. It's not currently used anywhere, the only use in
sys_pipe.c was ifdeffed out due to stability problems in 2009-08-31.

While the commit states the stability problems were present also on
sparc64 which used the emap fallback, I think the uvm_emap.c fallback
pmap_kenter_pa()/pmap_kremove() are actually not safe either.

Actual MD support for it was ever implemented only on x86. The emap
support complicates the already quite unwieldy x86 pmap, and I think
it makes sense to drop this unused code to lower the maintenance
overhead. Dropping this would certainly simplify my other work on PCID
support for x86.

Opinions?

Jaromir