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

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Message-ID: <516EAF31.8000107@linux.intel.com>
Date:	Wed, 17 Apr 2013 07:18:25 -0700
From:	Darren Hart <dvhart@...ux.intel.com>
To:	zhang.yi20@....com.cn
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: Re: [PATCH] futex: bugfix for futex-key conflict when futex use hugepage



On 04/17/2013 02:55 AM, zhang.yi20@....com.cn wrote:
> Darren Hart <dvhart@...ux.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
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