linux-kernel - Re: 2.6.29 pat issue

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Date:	Tue, 10 Mar 2009 10:42:39 -0700
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Thomas Hellstrom <thellstrom@...are.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

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

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