linux-kernel - Re: Re : Re : sparsemem usage

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Message-Id: <20060803181909.928b913b.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 3 Aug 2006 18:19:09 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	moreau francis <francis_moreau2000@...oo.fr>
Cc:	alan@...rguk.ukuu.org.uk, linux-kernel@...r.kernel.org,
	apw@...dowen.org
Subject: Re: Re : Re : sparsemem usage

On Thu, 3 Aug 2006 09:07:06 +0000 (GMT)
moreau francis <francis_moreau2000@...oo.fr> wrote:

> Alan Cox wrote:
> >
> > Mapping out parts of a section is quite normal - think about the 640K to
> > 1Mb hole in PC memory space.
> 
> OK. But I'm still worry. Please consider the following code
> 
>        for (...; ...; ...) {
>                 [...]
>                 if (pfn_valid(i))
>                        num_physpages++;
>                 [...]
>         }
> 
> In that case num_physpages won't store an accurate value. Still it will be
> used by the kernel to make some statistic assumptions on other kernel
> data structure sizes.
> 
In my understanding, pfn_valid() just returns "the page has page struct or not".
So, don't use pfn_valid() to count physical pages..


-Kame

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