linux-kernel - Re: 2.6.29 pat issue

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Message-ID: <49B781B6.3060704@vmware.com>
Date:	Wed, 11 Mar 2009 10:17:42 +0100
From:	Thomas Hellstrom <thellstrom@...are.com>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: 2.6.29 pat issue

Pallipadi, Venkatesh wrote:
> On Tue, 2009-03-10 at 01:22 -0700, Thomas Hellstrom wrote:
>   
>> Pallipadi, Venkatesh wrote:
>>     
>>> On Fri, Mar 06, 2009 at 03:44:07PM -0800, Thomas Hellstrom wrote:
>>>   
>>>       
>>>> We get the warning when we insert RAM pages using vm_insert_pfn().
>>>> Having normal RAM pages backing a PFN papping is a valid thing.
>>>>
>>>>     
>>>>         
>>> OK. Below is the updated patch that should fix this fully. Can you confirm?
>>>
>>> Thanks,
>>> Venki
>>>
>>>   
>>>       
>> Yes, this patch should fix the problem. I'm still concerned about the 
>> overhead of going through the
>> RAM test for each inserted page.
>>
>> Why can't a pfn_valid() test be used in vm_insert_pfn()?
>>
>>     
>
> Because we may have to track the RAM pages as well in future. We are
> changing the e820 RAM check and making it use pfn_valid. But, for that
> we have to change more things in tracking of RAM pages. Today we use one
> bit in page struct without any refcounting. But, more changes there are
> on ts way. This change here should keep the current kernel fine without
> any regression.
>
> Thanks,
> Venki
>
>   
Ok, I understand.
and yes, the regression should be fixed with the patch.

Thanks,
Thomas


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