Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966788Ab3DQPvi (ORCPT ); Wed, 17 Apr 2013 11:51:38 -0400 Received: from mga09.intel.com ([134.134.136.24]:15778 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966025Ab3DQPvh (ORCPT ); Wed, 17 Apr 2013 11:51:37 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,494,1363158000"; d="scan'208";a="319767439" Message-ID: <516EC508.6070200@linux.intel.com> Date: Wed, 17 Apr 2013 08:51:36 -0700 From: Darren Hart User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Dave Hansen CC: zhang.yi20@zte.com.cn, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Dave Hansen Subject: Re: [PATCH] futex: bugfix for futex-key conflict when futex use hugepage References: <516EAF31.8000107@linux.intel.com> <516EBF23.2090600@sr71.net> In-Reply-To: <516EBF23.2090600@sr71.net> X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1714 Lines: 42 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/