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

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Date:	Tue, 16 Sep 2014 12:38:10 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Michal Hocko <mhocko@...e.cz>, <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

On Tue, Sep 16, 2014 at 03:14:01PM +0900, Tejun Heo wrote:
> I don't think marking config options as "UNDER DEVELOPMENT" in its
> help documentation means anything.  It's a rather silly thing to do.
> Not many people pay much attention to the help texts and once somebody
> somewhere enabled the option for a distro, it's as free in the wild as
> any other kernel feature and CONFIG_MEMCG_KMEM is enabled by a lot of
> distros.  The same goes with the "debug" controller.  It doesn't mean
> much that it has "debug" in its name.  Once it's out in the wild,
> there will be someone making use of it in some weird way.
> 
> If a debug feature has to be in the mainline kernel, the fact that
> it's a debug feature must be explicitly chosen in each use.  IOW, gate
> it by an unwieldy boot param which makes it painfully clear that it's
> enabling an unstable debug feature and print out a loud warning
> message about it.
> 
> As it currently stands, CONFIG_MEMCG_KMEM is as good as any other
> enabled kernel option.  The help text saying that it's experimental
> does not mean anything especially when it doesn't even depend on
> CONFIG_BROKEN.
> 
> So, the argument "the option was explained as experimental in help
> text" doesn't fly at all.  We can still try to deprecate it gradually
> if the cleanup seems worthwhile; however, with v2 interface pending,
> I'm not sure how meaningful that'd be.  We'd have to carry quite a bit
> of v1 code around anyway and I'd like to keep v1 interface as static
> as possible.  No reason to shake that at this point.

Fair enough, thank you for the clarification. I hope we'll be able to
get rid of it in a year or two when cgroup v2 becomes stable.

Thanks,
Vladimir
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