|| ||Andi Kleen <ak-AT-linux.intel.com> |
|| ||"Michael Kerrisk (man-pages)" <mtk.manpages-AT-gmail.com> |
|| ||Re: [PATCH] MM: Support more pagesizes for MAP_HUGETLB/SHM_HUGETLB v6 |
|| ||Mon, 22 Oct 2012 08:36:33 -0700|
|| ||Andi Kleen <andi-AT-firstfloor.org>, akpm-AT-linux-foundation.org,
Hillf Danton <dhillf-AT-gmail.com>|
|| ||Article, Thread
> 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 ==
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
> > 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
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