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

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Date:	Wed, 26 Sep 2012 21:53:09 +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 09/26/2012 09:44 PM, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Wed, Sep 26, 2012 at 10:36 AM, Glauber Costa <glommer@...allels.com> wrote:
>> This was discussed multiple times. Our interest is to preserve existing
>> deployed setup, that were tuned in a world where kmem didn't exist.
>> Because we also feed kmem to the user counter, this may very well
>> disrupt their setup.
> 
> So, that can be served by .kmem_accounted at root, no?
> 
>> User memory, unlike kernel memory, may very well be totally in control
>> of the userspace application, so it is not unreasonable to believe that
>> extra pages appearing in a new kernel version may break them.
>>
>> It is actually a much worse compatibility problem than flipping
>> hierarchy, in comparison
> 
> Again, what's wrong with one switch at the root?
> 

I understand your trauma about over flexibility, and you know I share of
it. But I don't think there is any need to cap it here. Given kmem
accounted is perfectly hierarchical, and there seem to be plenty of
people who only care about user memory, I see no reason to disallow a
mixed use case here.

I must say that for my particular use case, enabling it unconditionally
would just work, so it is not that what I have in mind.

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