linux-kernel - Re: 2.6.29 pat issue

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Message-ID: <20090311093338.GC12814@elte.hu>
Date:	Wed, 11 Mar 2009 10:33:38 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Hellstrom <thellstrom@...are.com>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"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


* Thomas Hellstrom <thellstrom@...are.com> wrote:

> 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.

Good. Venki, mind resending the patch against tip:master, with a 
proper subject line, changelog and Acked-by in place? Thanks,

	Ingo
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