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 07C35B6F73 for ; Fri, 11 Mar 2011 03:38:15 +1100 (EST) Date: Thu, 10 Mar 2011 08:38:09 -0800 From: Andi Kleen To: Stephen Wilson Subject: Re: [PATCH 0/5] make *_gate_vma accept mm_struct instead of task_struct II Message-ID: <20110310163809.GA20675@alboin.amr.corp.intel.com> References: <1299630721-4337-1-git-send-email-wilsons@start.ca> <20110310160032.GA20504@alboin.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20110310160032.GA20504@alboin.amr.corp.intel.com> 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 Thu, Mar 10, 2011 at 08:00:32AM -0800, Andi Kleen wrote: > 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. Hmm I see you're only setting it on exec time actually on rereading the patches. I thought you were changing TS_COMPAT which is in the syscall path. Never mind. I have no problems with doing such a change on exec time. -Andi