On 04/17/2013 08:26 AM, Dave Hansen wrote: > On 04/17/2013 07:18 AM, Darren Hart wrote: >>>> This also needs a comment in futex.h describing the usage of the offset >>>> field in union futex_key as well as above get_futex_key describing the >>>> key for shared mappings. >>>> >>> As far as I know , the max size of one hugepage is 1 GBytes for x86 cpu. >>> Can some other cpus support greater hugepage even more than 4 GBytes? If >>> so, we can change the type of 'offset' from int to long to avoid >>> truncating. >> >> I discussed this with Dave Hansen, on CC, and he thought we needed 9 >> bits, so even on x86 32b we should be covered. > > I think the problem is actually on 64-bit since you still only have > 32-bits in an 'int' there. > > I guess it's remotely possible that we could have some > mega-super-huge-gigantic pages show up in hardware some day, or that > somebody would come up with software-only one. I bet there's a lot more > code that will break in the kernel than this futex code, though. > > The other option would be to start #defining some build-time constant > for what the largest possible huge page size is, then BUILD_BUG_ON() it. > > Or you can just make it a long ;) If we make it a long I'd want to see futextest performance tests before and after. Messing with the futex_key has been known to have bad results in the past :-) -- Darren Hart Intel Open Source Technology Center Yocto Project - Technical Lead - Linux Kernel -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>