Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758302AbZFOPIa (ORCPT ); Mon, 15 Jun 2009 11:08:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754854AbZFOPIX (ORCPT ); Mon, 15 Jun 2009 11:08:23 -0400 Received: from smtp3.ultrahosting.com ([74.213.175.254]:37177 "EHLO smtp.ultrahosting.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752467AbZFOPIW (ORCPT ); Mon, 15 Jun 2009 11:08:22 -0400 Date: Mon, 15 Jun 2009 11:05:42 -0400 (EDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Pekka Enberg cc: torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, kamezawa.hiroyu@jp.fujitsu.com, lizf@cn.fujitsu.com, mingo@elte.hu, npiggin@suse.de, yinghai@kernel.org, benh@kernel.crashing.org Subject: Re: [GIT PULL v2] Early SLAB fixes for 2.6.31 In-Reply-To: <1245077891.23207.48.camel@penberg-laptop> Message-ID: References: <1245077891.23207.48.camel@penberg-laptop> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1197 Lines: 31 On Mon, 15 Jun 2009, Pekka Enberg wrote: > > Dont do it there. Only modify the slow path. > > > > Look at __might_sleep(). It already has an exception for system_state != > > RUNNING. If it still triggers then add to the condition there. > > But does this matter? When the debugging options are turned off, there > are no users for "real_gfp" and thus GCC optimizes everything away. For > debugging configs, the extra cacheline load doesn't matter, does it? It cleaner to have the fastpath as small as possible. Having unused variables in there is a bit confusing. Also the path is performance critical. That may not matter for the debug case in some sitiations. But there are people that keep the debugging options on. Better to limit the impact as much as possible. And the "extra cacheline load does not matter" reasoning can only be applied so many times. An extra cacheline load increases the cache foot print of the fast path after all. -- 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/