Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754584AbaKDQAu (ORCPT ); Tue, 4 Nov 2014 11:00:50 -0500 Received: from mga14.intel.com ([192.55.52.115]:61125 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753293AbaKDQAo (ORCPT ); Tue, 4 Nov 2014 11:00:44 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,862,1389772800"; d="scan'208";a="411230156" Message-ID: <5458F819.2010503@intel.com> Date: Tue, 04 Nov 2014 08:00:25 -0800 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Thomas Gleixner CC: Ren Qiaowei , "H. Peter Anvin" , Ingo Molnar , x86@kernel.org, Linux-MM , linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@linux-mips.org Subject: Re: [PATCH v9 11/12] x86, mpx: cleanup unused bound tables References: <1413088915-13428-1-git-send-email-qiaowei.ren@intel.com> <1413088915-13428-12-git-send-email-qiaowei.ren@intel.com> <544DB873.1010207@intel.com> <5457EB67.70904@intel.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/03/2014 01:29 PM, Thomas Gleixner wrote: > On Mon, 3 Nov 2014, Dave Hansen wrote: > That's not really true. You can evaluate that information with > mmap_sem held for read as well. Nothing can change the mappings until > you drop it. So you could do: > > down_write(mm->bd_sem); > down_read(mm->mmap_sem; > evaluate_size_of_shm_to_unmap(); > clear_bounds_directory_entries(); > up_read(mm->mmap_sem); > do_the_real_shm_unmap(); > up_write(mm->bd_sem); > > That should still be covered by the above scheme. Yep, that'll work. It just means rewriting the shmdt()/mremap() code to do a "dry run" of sorts. Do you have any concerns about adding another mutex to these paths? munmap() isn't as hot of a path as the allocation side, but it does worry me a bit that we're going to perturb some workloads. We might need to find a way to optimize out the bd_sem activity on processes that never used MPX. -- 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/