From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Date: Thu, 10 Mar 2011 16:00:32 +0000 Subject: Re: [PATCH 0/5] make *_gate_vma accept mm_struct instead of Message-Id: <20110310160032.GA20504@alboin.amr.corp.intel.com> List-Id: References: <1299630721-4337-1-git-send-email-wilsons@start.ca> In-Reply-To: <1299630721-4337-1-git-send-email-wilsons@start.ca> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 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