Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753753Ab3JCIzc (ORCPT ); Thu, 3 Oct 2013 04:55:32 -0400 Received: from mail-qa0-f48.google.com ([209.85.216.48]:42547 "EHLO mail-qa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753397Ab3JCIz3 (ORCPT ); Thu, 3 Oct 2013 04:55:29 -0400 MIME-Version: 1.0 In-Reply-To: <20131002203107.GY3081@twins.programming.kicks-ass.net> References: <20131002130143.GF28601@twins.programming.kicks-ass.net> <20131002133759.GH28601@twins.programming.kicks-ass.net> <20131002190001.GX3081@twins.programming.kicks-ass.net> <20131002203107.GY3081@twins.programming.kicks-ass.net> Date: Thu, 3 Oct 2013 10:55:28 +0200 Message-ID: Subject: Re: [RFC] perf: mmap2 not covering VM_CLONE regions From: Stephane Eranian To: Peter Zijlstra Cc: Kees Cook , Ingo Molnar , LKML , "mingo@elte.hu" , "ak@linux.intel.com" , Arnaldo Carvalho de Melo , David Ahern , Jiri Olsa , Hugh Dickins , Linus Torvalds , Andrew Morton Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1558 Lines: 32 On Wed, Oct 2, 2013 at 10:31 PM, Peter Zijlstra wrote: > On Wed, Oct 02, 2013 at 12:38:54PM -0700, Kees Cook wrote: >> On Wed, Oct 2, 2013 at 12:00 PM, Peter Zijlstra wrote: >> > On Wed, Oct 02, 2013 at 11:10:15AM -0700, Kees Cook wrote: >> >> Seems like a simple enough solution. Surely there must be a catch. :) >> > >> > I didn't want to add this to the core mm just for perf.. >> >> It seems like it would be pretty inexpensive. It might also be >> valuable in other situations. Not that I can think of any at the >> moment. Additionally, it could likely be hidden by a CONFIG, so that >> if perf isn't built in, there's no change? > > You optimist, you think you can build a kernel without perf? ;-) > > Its just that I would hate to add more completely global state to the > fork() path. The tasklist_lock might be hard to crack, but at least the > pid-hash could use per bucket locks (it doesn't apparently). > > I suppose people don't really care that much about fork() performance; > which is sad. KSM and THP also add their own global locks :-( I don't know the MM code but I assume that that vm_mm struct is allocated dynamically and maybe you already grabbing a lock while doing this. Could we leverage that lock to increment a global generation number? -- 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/