Re: [00/17] Large Blocksize Support V3

[Nick Piggin]

Christoph Lameter wrote:
> On Thu, 26 Apr 2007, Nick Piggin wrote:
>
>
> > Christoph Lameter wrote:
> >
> > > On Thu, 26 Apr 2007, Nick Piggin wrote:
> > >
> > >
> > >
> > > > But I maintain that the end result is better than the fragmentation
> > > > based approach. A lot of people don't actually want a bigger page
> > > > cache size, because they want efficient internal fragmentation as
> > > > well, so your radix-tree based approach isn't really comparable.
> > >
> > >
> > > Me? Radix tree based approach? That approach is in the kernel. Do not create
> > > a solution where there is no problem. If we do not want to support large
> > > blocksizes then lets be honest and say so instead of redefining what a block
> > > is. The current approach is fine if one is satisfied with scatter gather and
> > > the VM overhead coming with handling these pages. I fail to see what any of
> > > what you are proposing would add to that.
> >
> > I'm not just making this up. Fragmentation. OK?
>
>
> Yes you are. If you want to avoid fragmentation by restricting the OS to 
> 4k alone then the radix tree is sufficient to establish the order of pages 
> in a mapping. The only problem is to get an array of pointers to a 
> sequence of pages together by reading through the radix tree. I do not 
> know what else would be needed.

No. We have avoided fragmentation up until now. We avoid fragmentation like
the plague because it is crap. What _I_ do not want to do is add some
patches that make it work a bit better and everyone think's that's a signal
that it is a good idea to start using higher order allocations wherever
possible.

--
SUSE Labs, Novell Inc.
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