linux-kernel - Re: [PATCH 1/7] Introduce the pagetable_operations and associated helper macros.

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Date:	Wed, 21 Mar 2007 09:50:30 -0500
From:	Adam Litke <agl@...ibm.com>
To:	Dave Hansen <hansendc@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	William Lee Irwin III <wli@...omorphy.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ken Chen <kenchen@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] Introduce the pagetable_operations and associated
	helper macros.

On Tue, 2007-03-20 at 16:24 -0700, Dave Hansen wrote:
> On Mon, 2007-03-19 at 13:05 -0700, Adam Litke wrote:
> > 
> > +#define has_pt_op(vma, op) \
> > +       ((vma)->pagetable_ops && (vma)->pagetable_ops->op)
> > +#define pt_op(vma, call) \
> > +       ((vma)->pagetable_ops->call) 
> 
> Can you get rid of these macros?  I think they make it a wee bit harder
> to read.  My brain doesn't properly parse the foo(arg)(bar) syntax.  
> 
> +       if (has_pt_op(vma, copy_vma))
> +               return pt_op(vma, copy_vma)(dst_mm, src_mm, vma);
> 
> +       if (vma->pagetable_ops && vma->pagetable_ops->copy_vma)
> +               return vma->pagetable_ops->copy_vma(dst_mm, src_mm, vma);
> 
> I guess it does lead to some longish lines.  Does it start looking
> really nasty?

Yeah, it starts to look pretty bad.  Some of these calls are in code
that is already indented several times.

> If you're going to have them, it might just be best to put a single
> unlikely() around the macro definitions themselves to keep anybody from
> having to open-code it for any of the users.  

It should be pretty easy to wrap has_pt_op() with an unlikely().  Good
suggestion.

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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