Messages in this thread | | | Date | Mon, 22 Oct 2012 08:36:33 -0700 | From | Andi Kleen <> | Subject | Re: [PATCH] MM: Support more pagesizes for MAP_HUGETLB/SHM_HUGETLB v6 |
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> Not sure of your notation there. I assume 31..27 means 5 bits (32 > through to 28 inclusive, 27 excluded). That gives you just 2^31 ==
[27...31]
You're right it's only 5 bits, so just 2GB.
Thinking about it more PowerPC has a 16GB page, so we probably need to move this to prot.
However I'm not sure if any architectures use let's say the high 8 bits of prot.
> > But there seems an obvious solution here: given your value in those > bits (call it 'n'), the why not apply a multiplier. I mean, certainly > you never want a value <= 12 for n, and I suspect that the reasonable > minimum could be much larger (e.g., 2^16). Call that minimum M. Then > you could interpret the value in your bits as meaning a page size of > > (2^n) * M
I considered that, but it would seem ugly and does not add that many bits.
> > > So this will use up all remaining flag bits now. > > On the other hand, that seems really bad. It looks like that kills the > ability to further extend the mmap() API with new flags in the future. > It doesn't sound like we should be doing that.
You can always add flags to PROT or add a mmap3(). Has been done before. Or just don't do any new MAP_SECURITY_HOLEs
-Andi
-- ak@linux.intel.com -- Speaking for myself only
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