Re: [patch 17/18] x86: add hugepagesz option on 64-bit

[Nishanth Aravamudan <nacc@us.ibm.com>]

On 30.04.2008 [22:45:09 +0200], Andi Kleen wrote:
> > If so, I'll hold off
> > on any further review.
> 
> That's not what I asked for.  Some of your comments were very useful
> by pointing to real bugs and other problems, just some others were
> not. Please continue reviewing, just make sure that all the comments
> are focused on improving that particular code in the concrete current
> application.

I will focus on this, thanks for the feedback. Per my just-sent mail,
I'm not sure what the "concrete application" is for 1G pages --
either a custom application or using libhugetlbfs with 1G pages. And the
latter is where most of my comments are coming from. When I've been
making nit-picky comments, I've tried to prefix them with "Nit". Those
have mostly been cosmetic or style-issues that simply show up obviously
in the diffs.

> For example the bulk of the changes needed for PPC I expect will just
> be an additional add on patchkit.

I agree. But it might be nice to minimize the churn and be aware of any
gotchas ahead of time. Hence why I asked yourself and Nick as the
original authors about the separation between arch-independent and
arch-dependent code. x86_64 seems to be relatively easy in this regard,
while power requires more state per-hugepagesize.

> > > The hugetlbfs code actually doesn't claim that.
> > 
> > The hugetlb.c code is architecture independent and roughly generic (it
> > doesn't know a whole lot about the underlying architecture itself).
> > hstates are defined and used in this independent code -- hence my
> > perspective that we want to make sure it is flexible enough to handle
> > other architectures than x86_64, or at least easily extensible to them.
> 
> It is extensible to them, but with some further changes (that is what
> the patchkit claimed)
> 
> For power I think it would be best if you just started on the
> incremental patches needed (in fact there were already such an addon,
> perhaps that can be just improved)

Agreed, I'm starting to look at that with Jon.

> > Well, Nick was talking about adding the powerpc bits to his stack
> > when he submited for -mm, so these discussions should be happening
> > now, AFAICT.
> 
> The whole thing is work in progress and will undoubtedly change more
> before it is really used.  Nothing is put in stone yet.

Thanks,
Nish

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