From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 518176B04E3 for ; Mon, 31 Jul 2017 22:23:27 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id m80so797994wmd.4 for ; Mon, 31 Jul 2017 19:23:27 -0700 (PDT) Received: from mout.gmx.net (mout.gmx.net. [212.227.15.18]) by mx.google.com with ESMTPS id 74si233226wma.57.2017.07.31.19.23.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 31 Jul 2017 19:23:26 -0700 (PDT) Message-ID: <1501554199.5269.22.camel@gmx.de> Subject: Re: [PATCH 3/3] mm/sched: memdelay: memory health interface for systems and workloads From: Mike Galbraith Date: Tue, 01 Aug 2017 04:23:19 +0200 In-Reply-To: <20170731203839.GA5162@cmpxchg.org> References: <20170727153010.23347-1-hannes@cmpxchg.org> <20170727153010.23347-4-hannes@cmpxchg.org> <20170729091055.GA6524@worktop.programming.kicks-ass.net> <20170730152813.GA26672@cmpxchg.org> <20170731083111.tgjgkwge5dgt5m2e@hirez.programming.kicks-ass.net> <20170731184142.GA30943@cmpxchg.org> <1501530579.9118.43.camel@gmx.de> <20170731203839.GA5162@cmpxchg.org> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Peter Zijlstra , Ingo Molnar , Andrew Morton , Rik van Riel , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com On Mon, 2017-07-31 at 16:38 -0400, Johannes Weiner wrote: > On Mon, Jul 31, 2017 at 09:49:39PM +0200, Mike Galbraith wrote: > > On Mon, 2017-07-31 at 14:41 -0400, Johannes Weiner wrote: > > >=20 > > > Adding an rq counter for tasks inside memdelay sections should be > > > straight-forward as well (except for maybe the migration cost of that > > > state between CPUs in ttwu that Mike pointed out). > >=20 > > What I pointed out should be easily eliminated (zero use case). >=20 > How so? I was thinking along the lines of=C2=A0schedstat_enabled(). > > > That leaves the question of how to track these numbers per cgroup at > > > an acceptable cost. The idea for a tree of cgroups is that walltime > > > impact of delays at each level is reported for all tasks at or below > > > that level. E.g. a leave group aggregates the state of its own tasks, > > > the root/system aggregates the state of all tasks in the system; henc= e > > > the propagation of the task state counters up the hierarchy. > >=20 > > The crux of the biscuit is where exactly the investment return lies. > > =C2=A0Gathering of these numbers ain't gonna be free, no matter how har= d you > > try, and you're plugging into paths where every cycle added is made of > > userspace hide. >=20 > Right. But how to implement it sanely and optimize for cycles, and > whether we want to default-enable this interface are two separate > conversations. >=20 > It makes sense to me to first make the implementation as lightweight > on cycles and maintainability as possible, and then worry about the > cost / benefit defaults of the shipped Linux kernel afterwards. >=20 > That goes for the purely informative userspace interface, anyway. The > easily-provoked thrashing livelock I have described in the email to > Andrew is a different matter. If the OOM killer requires hooking up to > this metric to fix it, it won't be optional. But the OOM code isn't > part of this series yet, so again a conversation best had later, IMO. If that "the many must pay a toll to save the few" conversation ever happens, just recall me registering my boo/hiss in advance. =C2=A0I don't have to feel guilty about not liking the idea of making donations to feed the poor starving proggies ;-) -Mike -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org