From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx101.postini.com [74.125.245.101]) by kanga.kvack.org (Postfix) with SMTP id 5E82A6B0072 for ; Wed, 27 Jun 2012 04:59:54 -0400 (EDT) Message-ID: <4FEACAE8.6000500@parallels.com> Date: Wed, 27 Jun 2012 12:57:12 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH 2/2] memcg: first step towards hierarchical controller References: <1340725634-9017-1-git-send-email-glommer@parallels.com> <1340725634-9017-3-git-send-email-glommer@parallels.com> <20120626180451.GP3869@google.com> <20120626185542.GE27816@cmpxchg.org> <20120626191450.GT3869@google.com> <20120626205924.GH27816@cmpxchg.org> <20120626211907.GX3869@google.com> In-Reply-To: <20120626211907.GX3869@google.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: Johannes Weiner , cgroups@vger.kernel.org, linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, Michal Hocko , Andrew Morton >> And because there is nothing to gain, it is in addition really >> trivial to fix the insane setups by simply undoing the nesting, >> there is no downside for them. > > I have to disagree with that. Deployment sometimes can be very > painful. In some cases, even flipping single parameter in sysfs > depending on kernel version takes considerable effort. The behavior > has been the contract that we offered userland for quite some time > now. We shouldn't be changing that underneath them without any clear > way for them to notice it. Yes, and that's why once you deploy, you keep your updates to a minimum. Because hell, even *perfectly legitimate bug fixes* can change your behavior in a way you don't want. And you don't expect people to refrain from fixing bugs because of that. > >> The only point where I agree with you is that it may indeed be >> non-obvious to detect in case you were relying on the filesystem >> hierarchy not being reflected in the controller hierarchy. But even >> that depends on the usecase, whether it's a subtle performance >> regression or a total failure to execute a previously supported >> workload, which would be pretty damn obvious. > > And imagine that happening in serveral thousand machine cluster with > fairly complicated cgroup setup and kernel update rolling out for > subset of machine types. I would be screaming bloody murder. That is precisely why people in serious environments tend to run -stable, distro LTSes, or anything like that. Because they don't want any change, however minor, to potentially affect their stamped behavior. I am not proposing this patch to -stable, btw... -- 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