Re: [PATCH] MM: Support more pagesizes for MAP_HUGETLB/SHM_HUGETLB v6
From: Andi Kleen
Date: Mon Oct 22 2012 - 11:36:26 EST
> 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@xxxxxxxxxxxxxxx -- Speaking for myself only
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/