Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753480Ab1CJQBN (ORCPT ); Thu, 10 Mar 2011 11:01:13 -0500 Received: from mga14.intel.com ([143.182.124.37]:3268 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751249Ab1CJQAs (ORCPT ); Thu, 10 Mar 2011 11:00:48 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.62,296,1297065600"; d="scan'208";a="400673947" Date: Thu, 10 Mar 2011 08:00:32 -0800 From: Andi Kleen To: Stephen Wilson Cc: x86@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Benjamin Herrenschmidt , Paul Mackerras , Martin Schwidefsky , Heiko Carstens , linux390@de.ibm.com, Paul Mundt , Michel Lespinasse , Andrew Morton , Alexander Viro , linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/5] make *_gate_vma accept mm_struct instead of task_struct Message-ID: <20110310160032.GA20504@alboin.amr.corp.intel.com> References: <1299630721-4337-1-git-send-email-wilsons@start.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1299630721-4337-1-git-send-email-wilsons@start.ca> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1439 Lines: 31 On Tue, Mar 08, 2011 at 07:31:56PM -0500, Stephen Wilson wrote: > > Morally, the question of whether an address lies in a gate vma should be asked > with respect to an mm, not a particular task. > > Practically, dropping the dependency on task_struct will help make current and > future operations on mm's more flexible and convenient. In particular, it > allows some code paths to avoid the need to hold task_lock. > > The only architecture this change impacts in any significant way is x86_64. > The principle change on that architecture is to mirror TIF_IA32 via > a new flag in mm_context_t. The problem is -- you're adding a likely cache miss on mm_struct for every 32bit compat syscall now, even if they don't need mm_struct currently (and a lot of them do not) Unless there's a very good justification to make up for this performance issue elsewhere (including numbers) this seems like a bad idea. > This is the first of a two part series that implements safe writes to > /proc/pid/mem. I will be posting the second series to lkml shortly. These Making every syscall slower for /proc/pid/mem doesn't seem like a good tradeoff to me. Please solve this in some other way. -Andi -- 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/