linux-kernel - Re: [RFC][PATCH] don't show pgoff of vma if vma is pure ANON (was Re: mmotm 2009-01-12-16-53 uploaded)

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Date:	Wed, 14 Jan 2009 14:08:35 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Mike Waychison <mikew@...gle.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, yinghan@...gle.com
Subject: Re: [RFC][PATCH] don't show pgoff of vma if vma is pure ANON (was
 Re: mmotm 2009-01-12-16-53 uploaded)

On Wed, 14 Jan 2009, KAMEZAWA Hiroyuki wrote:
> Hmm, is this brutal ?
> 
> ==
> Recently, it's argued that what proc/pid/maps shows is ugly when a
> 32bit binary runs on 64bit host.
> 
> /proc/pid/maps outputs vma's pgoff member but vma->pgoff is of no use
> information is the vma is for ANON.
> By this patch, /proc/pid/maps shows just 0 if no file backing store.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---

Brutal, but sensible enough: revert to how things looked before
we ever starting putting vm_pgoff to work on anonymous areas.

I slightly regret losing that visible clue to whether an anonymous
vma has ever been mremap moved.  But have I ever actually used that
info?  No, never.

I presume you test !vma->vm_file so the lines fit in, fair enough.
But I think you'll find checkpatch.pl protests at "(!vma->vm_file)?"

I dislike its decisions on the punctuation of the ternary operator
- perhaps even more than Andrew dislikes the operator itself!
Do we write a space before a question mark? no: nor before a colon;
but I also dislike getting into checkpatch.pl arguments!

While you're there, I'd also be inclined to make task_nommu.c
use the same loff_t cast as task_mmu.c is using.

Hugh

> Index: mmotm-2.6.29-Jan13/fs/proc/task_mmu.c
> ===================================================================
> --- mmotm-2.6.29-Jan13.orig/fs/proc/task_mmu.c
> +++ mmotm-2.6.29-Jan13/fs/proc/task_mmu.c
> @@ -220,7 +220,8 @@ static void show_map_vma(struct seq_file
>  			flags & VM_WRITE ? 'w' : '-',
>  			flags & VM_EXEC ? 'x' : '-',
>  			flags & VM_MAYSHARE ? 's' : 'p',
> -			((loff_t)vma->vm_pgoff) << PAGE_SHIFT,
> +			(!vma->vm_file)? 0 :
> +				((loff_t)vma->vm_pgoff) << PAGE_SHIFT,
>  			MAJOR(dev), MINOR(dev), ino, &len);
>  
>  	/*
> Index: mmotm-2.6.29-Jan13/fs/proc/task_nommu.c
> ===================================================================
> --- mmotm-2.6.29-Jan13.orig/fs/proc/task_nommu.c
> +++ mmotm-2.6.29-Jan13/fs/proc/task_nommu.c
> @@ -143,7 +143,8 @@ static int nommu_vma_show(struct seq_fil
>  		   flags & VM_WRITE ? 'w' : '-',
>  		   flags & VM_EXEC ? 'x' : '-',
>  		   flags & VM_MAYSHARE ? flags & VM_SHARED ? 'S' : 's' : 'p',
> -		   (unsigned long long) vma->vm_pgoff << PAGE_SHIFT,
> +		   (!vma->vm_file) ? 0 :
> +			(unsigned long long) vma->vm_pgoff << PAGE_SHIFT,
>  		   MAJOR(dev), MINOR(dev), ino, &len);
>  
>  	if (file) {
> 
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