Re: 2G memory split

[Jens Axboe]

On Tue, Jan 10 2006, Jeff V. Merkey wrote:
> Alan Cox wrote:
> 
> >On Maw, 2006-01-10 at 09:56 -0700, Jeff V. Merkey wrote:
> > 
> >
> >>RH ES uses 4:4 which is ideal and superior to this hack.
> >>   
> >>
> >
> >Its a non trivial trade-off. 4/4 lets you run very large physical memory
> >systems much more efficiently than usual but you pay a cost on syscalls
> >and some other events when using the majority of processors. The 4/4
> >tricks also give most emulations (eg Qemu) serious heartburn trying to
> >emulate %cr3 reloading via mmap and other interfaces with high overhead
> >in relative terms.
> >
> >Of course AMD64 kind of shot the problem in the head once and for all.
> >
> > 
> >
> 
> Yep, they sure did.  Seriously, the 4:4 option should also be present 
> along with 3:1 and 2:2
> splits.  You should merge your RH work into this patch and allow both.  
> It would save me one less
> patch to maintain off the tree.

You can't compare the two patches, saying that 4:4 should go in because
configurable page offsets is merged is nonsense.

Note that I'm not advocating against 4:4 as such, I have no real
oppinion on that. It has its uses for sure, while it comes with a cost
for others.

-- 
Jens Axboe

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