linux-kernel - Re: [PATCH 4/4] hugetlb: add support for gigantic page allocation at runtime

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Date:	Tue, 8 Apr 2014 20:29:15 -0400
From:	Luiz Capitulino <lcapitulino@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mtosatti@...hat.com,
	aarcange@...hat.com, mgorman@...e.de, andi@...stfloor.org,
	davidlohr@...com, rientjes@...gle.com,
	isimatu.yasuaki@...fujitsu.com, yinghai@...nel.org, riel@...hat.com
Subject: Re: [PATCH 4/4] hugetlb: add support for gigantic page allocation
 at runtime

On Tue, 8 Apr 2014 15:51:02 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 7 Apr 2014 14:49:35 -0400 Luiz Capitulino <lcapitulino@...hat.com> wrote:
> 
> > > > ---
> > > >  arch/x86/include/asm/hugetlb.h |  10 +++
> > > >  mm/hugetlb.c                   | 177 ++++++++++++++++++++++++++++++++++++++---
> > > >  2 files changed, 176 insertions(+), 11 deletions(-)
> > > > 
> > > > diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
> > > > index a809121..2b262f7 100644
> > > > --- a/arch/x86/include/asm/hugetlb.h
> > > > +++ b/arch/x86/include/asm/hugetlb.h
> > > > @@ -91,6 +91,16 @@ static inline void arch_release_hugepage(struct page *page)
> > > >  {
> > > >  }
> > > >  
> > > > +static inline int arch_prepare_gigantic_page(struct page *page)
> > > > +{
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +static inline void arch_release_gigantic_page(struct page *page)
> > > > +{
> > > > +}
> > > > +
> > > > +
> > > >  static inline void arch_clear_hugepage_flags(struct page *page)
> > > >  {
> > > >  }
> > > 
> > > These are defined only on arch/x86, but called in generic code.
> > > Does it cause build failure on other archs?
> > 
> > Hmm, probably. The problem here is that I'm unable to test this
> > code in other archs. So I think the best solution for the first
> > merge is to make the build of this feature conditional to x86_64?
> > Then the first person interested in making this work in other
> > archs add the generic code. Sounds reasonable?
> 
> These functions don't actually do anything so if and when other
> architectures come along to implement this feature, their developers
> won't know what you were thinking when you added them.  So how about
> some code comments to explain their roles and responsibilities?
> 
> Or just delete them altogether and let people add them (or something
> similar) if and when the need arises.  It's hard to tell when one lacks
> telepathic powers, sigh.

That's exactly what I did for v2 (already posted).
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