linux-kernel - Re: [patch] hugetlb: remove dummy definitions of HPAGE_MASK and HPAGE

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Message-Id: <20111117155703.b8af6be5.akpm@linux-foundation.org>
Date:	Thu, 17 Nov 2011 15:57:03 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Daney <david.daney@...ium.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Robin Holt <holt@....com>
Subject: Re: [patch] hugetlb: remove dummy definitions of HPAGE_MASK and
 HPAGE_SIZE

On Thu, 17 Nov 2011 15:52:28 -0800
David Daney <ddaney.cavm@...il.com> wrote:

> A counter argument would be:
> 
> There are hundreds of places in the kernel where dummy definitions are 
> selected by !CONFIG_* so that we can do:
> 
>     if (test_something()) {
>        do_one_thing();
>     } else {
>        do_the_other_thing();
>     }
> 
> 
> Rather than:
> 
> #ifdef CONFIG_SOMETHING
>     if (test_something()) {
>        do_one_thing();
>     } else
> #else
>     {
>        do_the_other_thing();
>     }
> 
> 
> 
> We even do this all over the place with dummy definitions selected by 
> CONFIG_HUGETLB_PAGE, What exactly makes HPAGE_MASK special and not the 
> hundreds of other similar situations?

yup.  Look at free_pgtables():

		if (is_vm_hugetlb_page(vma)) {
			hugetlb_free_pgd_range(tlb, addr, vma->vm_end,
				floor, next? next->vm_start: ceiling);
		} else {

and

#define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) ({BUG(); 0; })

This is the same thing.
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