From mboxrd@z Thu Jan 1 00:00:00 1970 From: Balbir Singh Subject: Re: [-mm] Add an owner to the mm_struct (v7) Date: Fri, 04 Apr 2008 00:58:00 +0530 Message-ID: <47F52FC0.60305@linux.vnet.ibm.com> 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> Reply-To: balbir@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <6599ad830804031156w79366866yed9f8c3b8acf71fb@mail.gmail.com> Sender: linux-kernel-owner@vger.kernel.org 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 List-Id: linux-mm.kvack.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