linux-kernel - RE: [RFC] remap_pfn_range: store vm_pgoff for all linear_over_vma

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Date:	Thu, 23 Oct 2008 21:13:57 -0700
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Nick Piggin <npiggin@...e.de>
CC:	"hugh@...itas.com" <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: RE: [RFC] remap_pfn_range: store vm_pgoff for all
 linear_over_vma_region mappings

 

>-----Original Message-----
>From: Nick Piggin [mailto:npiggin@...e.de] 
>Sent: Thursday, October 23, 2008 6:08 PM
>To: Pallipadi, Venkatesh
>Cc: hugh@...itas.com; apkm@...ux-os.sc.intel.com; Ingo Molnar; 
>linux-kernel
>Subject: Re: [RFC] remap_pfn_range: store vm_pgoff for all 
>linear_over_vma_region mappings
>
>On Thu, Oct 23, 2008 at 03:09:14PM -0700, Venki Pallipadi wrote:
>> 
>> While working on x86 PAT, we are having some hurdles with tracking
>> remap_pfn_range() regions, as later we do not have any 
>information to say
>> whether that PFNMAP mapping is linear for the entire vma range or
>> it is smaller granularity regions within the vma.
>> 
>> A simple solution to this is to use vm_pgoff as an indicator for
>> linear mapping over the vma region. Currently, remap_pfn_range
>> only sets vm_pgoff only for COW mappings. Below patch changes the
>> logic and sets the vm_pgoff irrespective of COW.
>> 
>> >From our understanding of the code, this should not break anyone.
>> Just sending it as an RFC to get feedback on whether it is OK to do
>> something like this or are there any corner cases that we may
>> break or watch out for.
>> 
>> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
>> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
>
>Hmm, I can'tthink of why it would break, but I would like to see an
>entire patch. Obviously you won't try to decode this vma stuff
>directly from the PAT code, but just call mm helpers... ?
>

Yes. We are thinking of it as a call similar to is_cow_mapping().
May be is_linear_vma_mapping() or something like that. We should
have the rest of the patches by next week.

Thanks,
Venki
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