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

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Date:	Sat, 13 Sep 2014 02:55:16 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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

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.

Thanks.

-- 
tejun
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