From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760166AbYDCT2c (ORCPT ); Thu, 3 Apr 2008 15:28:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756056AbYDCT2Y (ORCPT ); Thu, 3 Apr 2008 15:28:24 -0400 Received: from e28smtp03.in.ibm.com ([59.145.155.3]:38249 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754107AbYDCT2X (ORCPT ); Thu, 3 Apr 2008 15:28:23 -0400 Message-ID: <47F52FC0.60305@linux.vnet.ibm.com> Date: Fri, 04 Apr 2008 00:58:00 +0530 From: Balbir Singh Reply-To: balbir@linux.vnet.ibm.com Organization: IBM User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 To: Paul Menage CC: Dave Hansen , Pavel Emelianov , Hugh Dickins , Sudhir Kumar , YAMAMOTO Takashi , lizf@cn.fujitsu.com, linux-kernel@vger.kernel.org, taka@valinux.co.jp, linux-mm@kvack.org, David Rientjes , Andrew Morton , KAMEZAWA Hiroyuki Subject: Re: [-mm] Add an owner to the mm_struct (v7) References: <20080403174433.26356.42121.sendpatchset@localhost.localdomain> <1207247113.21922.63.camel@nimitz.home.sr71.net> <47F52735.7090502@linux.vnet.ibm.com> <6599ad830804031156w79366866yed9f8c3b8acf71fb@mail.gmail.com> In-Reply-To: <6599ad830804031156w79366866yed9f8c3b8acf71fb@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paul Menage wrote: > On Thu, Apr 3, 2008 at 11:51 AM, Balbir Singh wrote: >> >> + * delay_group_leader() ensures that if the group leader is around >> >> + * we need not select a new owner. >> >> + */ >> >> + ret = (mm && (atomic_read(&mm->mm_users) > 1) && (mm->owner == p) && >> >> + !delay_group_leader(p)); >> >> + return ret; >> >> +} >> > >> > Ugh. Could you please spell this out a bit more. I find that stuff >> > above really hard to read. Something like: >> > >> > if (!mm) >> > return 0; >> > if (atomic_read(&mm->mm_users) <= 1) >> > return 0; >> > if (mm->owner != p) >> > return 0; >> > if (delay_group_leader(p)) >> > return 0; >> > return 1; >> > >> >> The problem with code above is 4 branch instructions and the code I have just 4 >> AND operations. > > They'll be completely equivalent to the compiler, due to the > short-circuit evaluation of && Aahh.. Yes.. my bad.. I keep under-estimating compilers and their potential to optimize Form (2) seems more readable, I'll move to that -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL