From: Andy Whitcroft <apw@shadowen.org>
To: Dave Hansen <haveblue@us.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
Christoph Hellwig <hch@infradead.org>,
Nick Piggin <npiggin@suse.de>,
Christoph Lameter <clameter@sgi.com>, Mel Gorman <mel@csn.ul.ie>
Subject: Re: [PATCH 4/4] vmemmap ppc64: convert VMM_* macros to a real function
Date: Thu, 02 Aug 2007 18:39:57 +0100 [thread overview]
Message-ID: <46B216ED.9090404@shadowen.org> (raw)
In-Reply-To: <1186072295.18414.257.camel@localhost>
Dave Hansen wrote:
> On Thu, 2007-08-02 at 10:25 +0100, Andy Whitcroft wrote:
>> +unsigned long __meminit vmemmap_section_start(struct page *page)
>> +{
>> + unsigned long offset = ((unsigned long)page) -
>> + ((unsigned long)(vmemmap));
>
> Isn't this basically page_to_pfn()? Can we use it here?
No, as that does direct subtraction of the two pointers. Our 'page'
here is not guarenteed to be aligned even to a struct page boundary.
When it is not so aligned the subtraction of the pointers is undefined.
Indeed when you do subtract them when the 'page' is not aligned you get
complete gibberish back and blammo's result.
-apw
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next prev parent reply other threads:[~2007-08-02 17:39 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-02 9:24 [PATCH 0/4] vmemmap updates to V6 Andy Whitcroft
2007-08-02 9:24 ` [PATCH 1/4] vmemmap: remove excess debugging Andy Whitcroft
2007-08-02 19:18 ` Christoph Lameter
2007-08-02 9:25 ` [PATCH 2/4] vmemmap: simplify initialisation code and reduce duplication Andy Whitcroft
2007-08-02 9:25 ` [PATCH 3/4] vmemmap: pull out the vmemmap code into its own file Andy Whitcroft
2007-08-02 13:26 ` Christoph Hellwig
2007-08-02 19:28 ` Christoph Lameter
2007-08-03 14:57 ` Andy Whitcroft
2007-08-03 16:58 ` Christoph Lameter
2007-08-02 9:25 ` [PATCH 4/4] vmemmap ppc64: convert VMM_* macros to a real function Andy Whitcroft
2007-08-02 16:31 ` Dave Hansen
2007-08-02 17:39 ` Andy Whitcroft [this message]
2007-08-02 18:00 ` Dave Hansen
2007-08-02 19:30 ` Christoph Lameter
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