linux-kernel - Re: [PATCH RFC] memcg: revert kmem.tcp accounting

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Message-Id: <20140912144326.a8d5153d7c91d220ea89924a@linux-foundation.org>
Date:	Fri, 12 Sep 2014 14:43:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Michal Hocko <mhocko@...e.cz>,
	Vladimir Davydov <vdavydov@...allels.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
	"David S. Miller" <davem@...emloft.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Glauber Costa <glommer@...il.com>,
	Pavel Emelianov <xemul@...allels.com>,
	Greg Thelen <gthelen@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH RFC] memcg: revert kmem.tcp accounting

On Sat, 13 Sep 2014 02:55:16 +0900 Tejun Heo <tj@...nel.org> wrote:

> Hello, guys.
> 
> On Fri, Sep 12, 2014 at 07:18:09PM +0200, Michal Hocko wrote:
> > On Fri 12-09-14 19:26:58, Vladimir Davydov wrote:
> > > memory.kmem.tcp.limit_in_bytes works as the system-wide tcp_mem sysctl,
> > > but per memory cgroup. While the existence of the latter is justified
> > > (it prevents the system from becoming unusable due to uncontrolled tcp
> > > buffers growth) the reason why we need such a knob in containers isn't
> > > clear to me.
> > 
> > Parallels was the primary driver for this change. I haven't heard of
> > anybody using the feature other than Parallels. I also remember there
> > was a strong push for this feature before it was merged besides there
> > were some complains at the time. I do not remember details (and I am
> > one half way gone for the weekend now) so I do not have pointers to
> > discussions.
> > 
> > I would love to get rid of the code and I am pretty sure that networking
> > people would love this go even more. I didn't plan to provide kmem.tcp.*
> > knobs for the cgroups v2 interface but getting rid of it altogether
> > sounds even better. I am just not sure whether some additional users
> > grown over time.
> > Nevertheless I am really curious. What has changed that Parallels is not
> > interested in kmem.tcp anymore?
> 
> So, I'd love to see this happen too but I don't think we can do this.
> People use published interface.  The usages might be utterly one-off
> and mental but let's please not underestimate the sometimes senseless
> creativity found in the wild.  We simply can't remove a bunch of
> control knobs like this.

17 files changed, 51 insertions(+), 761 deletions(-)

Sob.

Is there a convenient way of disabling the whole thing and adding a
please-tell-us printk?  If nobody tells us for a year or two then zap.

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