Re: [PATCH] futex: bugfix for futex-key conflict when futex use hugepage

Darren Hart
2013-04-17T14:18:50Z

On 04/17/2013 02:55 AM, zhang.yi20@zte.com.cn wrote:
> Darren Hart <dvhart@linux.intel.com> wrote on 2013/04/17 01:57:10:
>
>> Again, a functional testcase in futextest would be a good idea. This
>> helps validate the patch and also can be used to identify regressions in
>> the future.
>
> I will post the testcase code later.
>
>>
>> What is the max value of comp_idx? Are we at risk of truncating it?
>> Looks like not really from my initial look.
>>
>> 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.

--
Darren Hart
Intel Open Source Technology Center
Yocto Project - Technical Lead - Linux Kernel