From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754572Ab1G1OyS (ORCPT ); Thu, 28 Jul 2011 10:54:18 -0400 Received: from mail-wy0-f174.google.com ([74.125.82.174]:55369 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752681Ab1G1OyP (ORCPT ); Thu, 28 Jul 2011 10:54:15 -0400 Date: Thu, 28 Jul 2011 16:54:10 +0200 From: Frederic Weisbecker To: Paul Menage Cc: LKML , Andrew Morton , Li Zefan , Johannes Weiner , Aditya Kali Subject: Re: [PATCH 6/7] cgroups: Add res counter common ancestor searching Message-ID: <20110728145406.GI11820@somewhere.redhat.com> References: <1310393706-321-1-git-send-email-fweisbec@gmail.com> <1310393706-321-7-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 25, 2011 at 06:05:00PM -0700, Paul Menage wrote: > On Mon, Jul 11, 2011 at 7:15 AM, Frederic Weisbecker wrote: > > Add a new API to find the common ancestor between two resource > > counters. This includes the passed resource counter themselves. > > > > Signed-off-by: Frederic Weisbecker > > Acked-by: Paul Menage > > There's something distasteful about doing an O(N^2) search on every > charge/uncharge operation, but I guess in general N isn't going to be > more than 2 or 3 so it's not worth optimizing. > > If you wanted to avoid the N^2 search then you could add a "depth" > field in struct res_counter, which would be initialized to > parent->depth+1, and then easily get both r1 and r2 to the same depth > before proceeding up the tree in lock step, but that would bloat all > instances of res_counter, which might work out as more expensive in > the long run. Yeah it only happens on slow paths and probably cgroups hierarchies don't tend to be so deep. But if that's a problem we can still optimize the way you said, and perhaps move that depth field into the struct task_counter instead. Thanks. > > Paul > > > Cc: Paul Menage > > Cc: Li Zefan > > Cc: Johannes Weiner > > Cc: Aditya Kali > > --- > >  include/linux/res_counter.h |    2 ++ > >  kernel/res_counter.c        |   19 +++++++++++++++++++ > >  2 files changed, 21 insertions(+), 0 deletions(-) > > > > diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h > > index 8c421ac..354ed30 100644 > > --- a/include/linux/res_counter.h > > +++ b/include/linux/res_counter.h > > @@ -139,6 +139,8 @@ void res_counter_uncharge_until(struct res_counter *counter, struct res_counter > >                                unsigned long val); > >  void res_counter_uncharge(struct res_counter *counter, unsigned long val); > > > > +struct res_counter *res_counter_common_ancestor(struct res_counter *l, struct res_counter *r); > > + > >  /** > >  * res_counter_margin - calculate chargeable space of a counter > >  * @cnt: the counter > > diff --git a/kernel/res_counter.c b/kernel/res_counter.c > > index 39f2513..1b2efd6 100644 > > --- a/kernel/res_counter.c > > +++ b/kernel/res_counter.c > > @@ -102,6 +102,25 @@ void res_counter_uncharge(struct res_counter *counter, unsigned long val) > >        res_counter_uncharge_until(counter, NULL, val); > >  } > > > > +struct res_counter * > > +res_counter_common_ancestor(struct res_counter *r1, struct res_counter *r2) > > +{ > > +       struct res_counter *iter; > > + > > +       while (r1) { > > +               iter = r2; > > +               while (iter) { > > +                       if (iter == r1) > > +                               return iter; > > +                       iter = iter->parent; > > +               } > > + > > +               r1 = r1->parent; > > +       } > > + > > +       return NULL; > > +} > > + > >  static inline unsigned long long * > >  res_counter_member(struct res_counter *counter, int member) > >  { > > -- > > 1.7.5.4 > > > >