Messages in this thread | | | From | "Ray Bryant" <> | Subject | Re: [PATCH/RFC] Shared page tables | Date | Mon, 23 Jan 2006 18:53:54 -0600 |
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On Monday 23 January 2006 18:39, Andi Kleen wrote: > On Tuesday 24 January 2006 01:16, Ray Bryant wrote: > > On Monday 23 January 2006 17:58, Ray Bryant wrote: > > <snip> > > > > > ... And what kind of alignment constraints do we end up > > > under in order to make the sharing happen? (My guess would be that > > > there aren't any such constraints (well, page alignment.. :-) if we > > > are just sharing pte's.) > > > > Oh, obviously that is not right as you have to share full pte pages. So > > on x86_64 I'm guessing one needs 2MB alignment in order to get the > > sharing to kick in, since a pte page maps 512 pages of 4 KB each. > > The new randomized mmaps will likely actively sabotate such alignment. I > just added them for x86-64. > > -Andi
Hmmm, does that mean there is a fundamental conflict between the desire to share pte's and getting good cache coloring behavior?
Isn't it the case that if the region is large enough (say >> 2MB), that randomized mmaps will just cause the first partial page of pte's to not be shareable, and as soon as we have a full pte page mapped into the file that the full pte pages will be shareable, etc, until the last (partial) pte page is not shareable?
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-- Ray Bryant AMD Performance Labs Austin, Tx 512-602-0038 (o) 512-507-7807 (c)
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