From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751375AbcGNReL (ORCPT <rfc822;w@1wt.eu>);
	Thu, 14 Jul 2016 13:34:11 -0400
Received: from mx1.redhat.com ([209.132.183.28]:35099 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751098AbcGNReI (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Thu, 14 Jul 2016 13:34:08 -0400
Date: Thu, 14 Jul 2016 19:34:27 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        John Stultz <john.stultz@linaro.org>, Ingo Molnar <mingo@redhat.com>,
        lkml <linux-kernel@vger.kernel.org>,
        Dmitry Shmidt <dimitrysh@google.com>,
        Rom Lemarchand <romlem@google.com>, Colin Cross <ccross@google.com>,
        Todd Kjos <tkjos@google.com>
Subject: Re: Severe performance regression w/ 4.4+ on Android due to cgroup
	locking changes
Message-ID: <20160714173426.GC13434@redhat.com>
References: <20160713221750.GR7094@linux.vnet.ibm.com> <CALAqxLU880FGWM+sCha1LAi8KCtzreG2jrMEPU92PSHy2tOOJg@mail.gmail.com> <20160713230238.GU7094@linux.vnet.ibm.com> <20160713230404.GA2197@linux.vnet.ibm.com> <20160714113505.GC15005@htj.duckdns.org> <20160714120428.GZ30154@twins.programming.kicks-ass.net> <20160714120845.GE15005@htj.duckdns.org> <20160714122049.GB30154@twins.programming.kicks-ass.net> <20160714150715.GJ15005@htj.duckdns.org> <20160714163211.GE30154@twins.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20160714163211.GE30154@twins.programming.kicks-ass.net>
User-Agent: Mutt/1.5.18 (2008-05-17)
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Thu, 14 Jul 2016 17:34:07 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 07/14, Peter Zijlstra wrote:
>
> But I really think that this Android usecase invalidates the premise of
> cgroups using a global lock.

Perhaps... but it would be nice to have a global lock for cgroups (and in
fact probably unify it with dup_mmap_sem). And we can't simply revert that
change now.

I am wondering if this use-case is really Android-specific or not. Because,
once again, we can add a boot option or even run-time knob for
cgroup_threadgroup_rwsem. If it is really Android-specific, we do not want
to penalize fork/exit by default.

Oleg.