From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga03.intel.com (mga03.intel.com [143.182.124.21]) by ozlabs.org (Postfix) with ESMTP id 4C5FBB6F94 for ; Fri, 11 Mar 2011 03:10:54 +1100 (EST) Date: Thu, 10 Mar 2011 08:00:32 -0800 From: Andi Kleen To: Stephen Wilson 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 In-Reply-To: <1299630721-4337-1-git-send-email-wilsons@start.ca> Cc: linux-s390@vger.kernel.org, Paul Mundt , linux-sh@vger.kernel.org, x86@kernel.org, Heiko Carstens , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar , Paul Mackerras , Alexander Viro , "H. Peter Anvin" , Martin Schwidefsky , linux390@de.ibm.com, Thomas Gleixner , Michel Lespinasse , linuxppc-dev@lists.ozlabs.org, Andrew Morton List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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