linux-kernel - Re: [PATCH v3 04/13] kmem accounting basic infrastructure

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Date:	Thu, 27 Sep 2012 01:24:40 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Michal Hocko <mhocko@...e.cz>, <linux-kernel@...r.kernel.org>,
	<cgroups@...r.kernel.org>, <kamezawa.hiroyu@...fujitsu.com>,
	<devel@...nvz.org>, <linux-mm@...ck.org>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v3 04/13] kmem accounting basic infrastructure

On 09/27/2012 12:16 AM, Tejun Heo wrote:
> On Thu, Sep 27, 2012 at 12:02:14AM +0400, Glauber Costa wrote:
>> But think in terms of functionality: This thing here is a lot more
>> similar to swap than use_hierarchy. Would you argue that memsw should be
>> per-root ?
> 
> I'm fairly sure you can make about the same argument about
> use_hierarchy.  There is a choice to make here and one is simpler than
> the other.  I want the additional complexity justified by actual use
> cases which isn't too much to ask for especially when the complexity
> is something visible to userland.
> 
> So let's please stop arguing semantics.  If this is definitely
> necessary for some use cases, sure let's have it.  If not, let's
> consider it later.  I'll stop responding on "inherent differences."  I
> don't think we'll get anywhere with that.
> 

If you stop responding, we are for sure not getting anywhere. I agree
with you here.

Let me point out one issue that you seem to be missing, and you respond
or not, your call.

"kmem_accounted" is not a switch. It is an internal representation only.
The semantics, that we discussed exhaustively in San Diego, is that a
group that is not limited is not accounted. This is simple and consistent.

Since the limits are still per-cgroup, you are actually proposing more
user-visible complexity than me, since you are adding yet another file,
with its own semantics.

About use cases, I've already responded: my containers use case is kmem
limited. There are people like Michal that specifically asked for
user-only semantics to be preserved. So your question for global vs
local switch (that again, doesn't exist; only a local *limit* exists)
should really be posed in the following way:
"Can two different use cases with different needs be hosted in the same
box?"

> Michal, Johannes, Kamezawa, what are your thoughts?
>
waiting! =)

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