linux-kernel - Re: [PATCH] THP: need is_vma_temporary_stack() when reference transparent_hugepage

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Message-ID: <20120502175508.GC2410@redhat.com>
Date:	Wed, 2 May 2012 19:55:08 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Alex Shi <alex.shi@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, riel@...hat.com,
	mgorman@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] THP: need is_vma_temporary_stack() when reference
 transparent_hugepage_enabled

On Wed, May 02, 2012 at 11:17:23AM +0800, Alex Shi wrote:
> On 05/01/2012 07:05 AM, Andrew Morton wrote:
> 
> > On Sat, 28 Apr 2012 14:33:15 +0800
> > Alex Shi <alex.shi@...el.com> wrote:
> > 
> >> When the transparent_hugepage_enabled() used out of mm/,
> >> is_vma_temporary_stack() need be referenced. Otherwise, it has compile
> >> error.
> > 
> > This is a poor changelog - it doesn't tell us how this compilation
> > error comes about.  Is there some known build error in the mainline
> > kernel, or did you discover this when altering the kernel, or what?
> 
> > 
> 
> > One of the several reasons for this information is to permit others to
> > work out which kernel version(s) should be fixed.
> > 

I wanted to ask the same question.

> I am sorry for the unclear log!
> When I try to transparent_hugepage_enabled() in arch/x86/mm/tlb.c with
> huge_mm.h include: +#include <linux/huge_mm.h>. make give me the following
> error:

I already guessed it was for development code out of tree code but I
wasn't sure, thanks for the clarification.

> ...
>   CC      arch/x86/mm/srat.o
> arch/x86/mm/tlb.c: In function ‘flush_tlb_range’:
> arch/x86/mm/tlb.c:324:4: error: implicit declaration of function ‘is_vma_temporary_stack’ [-Werror=implicit-function-declaration]
> cc1: some warnings being treated as errors
> ...
> Since it is not convenitant for user to include 2 head files just for one 
> target function, I send this patch. 
> 
> > is_vma_temporary_stack() is already declared in rmap.h.  We should not
> > declare it in two places.

My preference would still be to remove the is_vma_temporary_stack and
use two vmas during mremap of execve, that would remove the "vma"
parameter from transparent_hugepage_enabled() but others prefers to
skip a vma allocation in execve and stick to is_vma_temporary_stack,
which is fair enough argument.

> Oh, yes. Since is_vma_temporay_stack is just used in rmap.c and huge_memory.c
> . is it better to move it to huge_mm.h?

I guess it was cleaner on rmap.h as this is not related to THP, but
clearly it works better in huge_mm.h (and rmap.h->mm.h->huge_mm.h is
included automatically) so the patch looks fine to me.

Thanks,
Andrea
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