linux-kernel - Re: [PATCH bugfix] proc/pagemap: correctly report non-present ptes and holes between vmas

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Date:	Mon, 30 Apr 2012 18:12:14 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	khlebnikov@...nvz.org
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>, ak@...ux.intel.com,
	xemul@...allels.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH bugfix] proc/pagemap: correctly report non-present ptes and holes between vmas

On Mon, Apr 30, 2012 at 11:19:27PM +0400, Konstantin Khlebnikov wrote:
> Naoya Horiguchi wrote:
> >Hi,
> >
> >On Sat, Apr 28, 2012 at 08:22:30PM +0400, Konstantin Khlebnikov wrote:
> >>This patch resets current pagemap-entry if current pte isn't present,
> >>or if current vma is over. Otherwise pagemap reports last entry again and again.
> >>
> >>non-present pte reporting was broken in commit v3.3-3738-g092b50b
> >>("pagemap: introduce data structure for pagemap entry")
> >>
> >>reporting for holes was broken in commit v3.3-3734-g5aaabe8
> >>("pagemap: avoid splitting thp when reading /proc/pid/pagemap")
> >>
> >>Signed-off-by: Konstantin Khlebnikov<khlebnikov@...nvz.org>
> >>Reported-by: Pavel Emelyanov<xemul@...allels.com>
> >>Cc: Naoya Horiguchi<n-horiguchi@...jp.nec.com>
> >>Cc: KAMEZAWA Hiroyuki<kamezawa.hiroyu@...fujitsu.com>
> >>Cc: Andi Kleen<ak@...ux.intel.com>
> >
> >Thanks for your efforts.
> >I confirmed that this patch fixes the problem on v3.4-rc4.
> >But originally (before the commits you pointed to above) initializing
> >pagemap entries (originally labelled with confusing 'pfn') were done
> >in for-loop in pagemap_pte_range(), so I think it's better to get it
> >back to things like that.
> >
> >How about the following?
> 
> I don't like this. Functions which returns void should always initialize its "output"
> argument, it much more clear than relying on preinitialized value.

OK, it makes sense.

Thanks,
Naoya
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