From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx173.postini.com [74.125.245.173]) by kanga.kvack.org (Postfix) with SMTP id 30A186B0006 for ; Thu, 18 Apr 2013 04:06:09 -0400 (EDT) In-Reply-To: <516EC508.6070200@linux.intel.com> References: <516EAF31.8000107@linux.intel.com> <516EBF23.2090600@sr71.net> <516EC508.6070200@linux.intel.com> Subject: Re: Re: [PATCH] futex: bugfix for futex-key conflict when futex use hugepage MIME-Version: 1.0 Message-ID: From: zhang.yi20@zte.com.cn Date: Thu, 18 Apr 2013 16:05:19 +0800 Content-Type: text/plain; charset="US-ASCII" Sender: owner-linux-mm@kvack.org List-ID: To: Darren Hart Cc: Dave Hansen , Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar , Peter Zijlstra , Thomas Gleixner Darren Hart wrote on 2013/04/17 23:51:36: > 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 :-) > > -- I have run futextest/performance/futex_wait for testing, 5 times before make it long: futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10215 Kiter/s futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 9862 Kiter/s futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10081 Kiter/s futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10060 Kiter/s futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10081 Kiter/s And 5 times after make it long: futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 9940 Kiter/s futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10204 Kiter/s futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 9901 Kiter/s futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10152 Kiter/s futex_wait: Measure FUTEX_WAIT operations per second Arguments: iterations=100000000 threads=256 Result: 10060 Kiter/s Seems OK, is it? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org