linux-kernel - Re: 2.6.23-rc1-mm1 sparsemem

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Message-ID: <46A8B33E.8010705@shadowen.org>
Date:	Thu, 26 Jul 2007 15:44:14 +0100
From:	Andy Whitcroft <apw@...dowen.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Andy Whitcroft <apw@...dowen.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, clameter@....com
Subject: Re: 2.6.23-rc1-mm1 sparsemem_vmemamp fix.

Andy Whitcroft wrote:
> KAMEZAWA Hiroyuki wrote:
>> Fix sparsemem_vmemmap init. sorry if known bug.
>>
>> This patch fixes page table handling in sparsemem_vmammap.
>>
>> Without this, part of vmem_map is not mapped because each section's start addr of
>> mem_map is not aligned to PGD/PMD/PUD. 
>> (In ia64, secion's mem_map size is 3670016bytes. )
>>
>> for example, 
>>
>>  addr     pmd_addr_end(addr_end)         addr + PMD_SIZE
>>   |XXXXXXXXXX|??????????????????????????????|XXXXXXXXXXXXXXXXXX
>>
>>   X ... initialized vmem_map
>>   ? ... not intialized
>>
>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> I think the code change below is safe enough.  I have not found it easy
> to understand your description above but I think that you are saying
> that if the section we are initialising is bigger than a PMD size, but
> falls offset from the PMD start we will initialise the end of the first
> PMD and the end of the second PMD and so on.  The "start" of the second
> PMD is missed.
> 
> Ahh yes, that I think is what your diagram shows.  Yes this is pretty
> clearly wrong for any sort of offset initialisation, and would be worse
> lower down in the hierachy.  This seems like a clean way to fix the bug.
>  Thanks for finding this.
> 
> Acked-by: Andy Whitcroft <apw@...dowen.org>

Andrew, I'll fold this one into a new version when I get through the
other feedback, but could you pull this into -mm on top for now as its a
boot issue.

-apw
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