Messages in this thread | | | Date | Thu, 18 Dec 2008 23:33:03 +0100 | From | Nick Piggin <> | Subject | Re: [patch 1/7] x86 PAT: store vm_pgoff for all linear_over_vma_region mappings - v3 |
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On Thu, Dec 18, 2008 at 02:10:57PM -0800, Pallipadi, Venkatesh wrote: > On Thu, Dec 18, 2008 at 01:27:28PM -0800, Nick Piggin wrote: > > > > This is fine by me, however: > > 1. Can you add some comments to say "this is not for core vm but for pat, > > oh and a pgoff of zero is not going to work". > > OK. Will add comments about both the points. > > > 2. Can you please justify to me (or the changelog) roughly why PAT wants > > to know if the mapping is linear or not? Presumably it has to handle > > both types? If performance wasn't an issue, then you could manually scan > > the ptes to verify (which would solve your zero-offset bug). etc. > > The main reason is performance. If we know it is linear, we can track the entire > region as one block and do the reserve free for entire region. But, if it is > not linear, then we have to reserve memtype of physical addresses page by page. > This will not be optimal as it will result in reserve and free becoming > slower. Almost all users that we find in kernel today (atleast in x86) are > all linear.
OK, so it is not a bug to miss the zero pgoff case then. That's good to know and should be added to comments.
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