Re: 2G memory split

["Jeff V. Merkey" <jmerkey@wolfmountaingroup.com>]

Jens Axboe wrote:

> 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.
>
>  
I agree and I appreciate your recognizing this. As it stands, if I need 
4:4 I just ship on ES3 and ES4. the 3:1
patch in the standard kernel is a very good thing, and you are to be 
commended for finally getting it in.

P.S. Your bio stuff works great.

Jeff
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