Messages in this thread | | | Date | Mon, 17 Nov 2008 03:30:19 +0100 | From | Nick Piggin <> | Subject | Re: [patch 2/8] x86 PAT: set VM_PFNMAP flag in vm_insert_pfn |
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On Fri, Nov 14, 2008 at 01:35:38PM -0800, Pallipadi, Venkatesh wrote: > > > >-----Original Message----- > >From: Nick Piggin [mailto:npiggin@suse.de] > >Sent: Thursday, November 13, 2008 6:06 PM > >To: Pallipadi, Venkatesh > >Cc: Ingo Molnar; Thomas Gleixner; H Peter Anvin; Hugh Dickins; > >Roland Dreier; Jesse Barnes; Jeremy Fitzhardinge; Arjan van de > >Ven; linux-kernel@vger.kernel.org; Siddha, Suresh B > >Subject: Re: [patch 2/8] x86 PAT: set VM_PFNMAP flag in vm_insert_pfn > > > >On Thu, Nov 13, 2008 at 10:47:23AM -0800, Pallipadi, Venkatesh wrote: > >> > >> Yes. It does. But, it calls a lower level insert_pfn() > >function. The lower > >> level insert_pfn() does not have any bug checks. But the higher level > >> vm_insert_pfn() checks for PFNMAP or MIXEDMAP. > > > >Yes, but is there anything extra you need to check for cache aliases in > >MIXEDMAP mappings? > > > > Yes. We need additional things to track MIXEDMAP and we are looking at that. > But, that is slightly more trickier than the general PFNMAP case. And > only in-tree user of MIXEDMAP is xip and that too it only uses it for > regular WB mapping. So, we thought we should fix the more common case > first here. > > With MIXEDMAP there is no way whether to distinguish whether insert_pfn > Or insert_page was used while looking at VMA. We can probably use PFNMAP > in addition to MIXEDMAP to indicate that, which will make things easier.
It's difficult because it can have either method for a single VMA, and a given address in the vma may even change over time (not with current code in kernel AFAIKS, but AXFS eventually might get to that point).
> But, we are still looking at that and trying to understand the change > implication.
OK: now I understand correctly. Getting PFNMAP working is an important first step. I agree.
Thanks, Nick
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