linux-kernel - Re: [PATCH v2 09/11] memcg: propagate kmem limiting information to children

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Message-ID: <50335C74.4000803@parallels.com>
Date:	Tue, 21 Aug 2012 14:01:24 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, <devel@...nvz.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH v2 09/11] memcg: propagate kmem limiting information to
 children

On 08/21/2012 02:00 PM, Michal Hocko wrote:
> On Tue 21-08-12 13:22:09, Glauber Costa wrote:
>> On 08/21/2012 11:54 AM, Michal Hocko wrote:
> [...]
>>> But maybe you have a good use case for that?
>>>
>> Honestly, I don't. For my particular use case, this would be always on,
>> and end of story. I was operating under the belief that being able to
>> say "Oh, I regret", and then turning it off would be beneficial, even at
>> the expense of the - self contained - complication.
>>
>> For the general sanity of the interface, it is also a bit simpler to say
>> "if kmem is unlimited, x happens", which is a verifiable statement, than
>> to have a statement that is dependent on past history. 
> 
> OK, fair point. We shouldn't rely on the history. Maybe
> memory.kmem.limit_in_bytes could return some special value like -1 in
> such a case?
> 

Way I see it, this is simplifying the code at the expense of
complicating the interface.

>> But all of those need of course, as you pointed out, to be traded off
>> by the code complexity.
>>
>> I am fine with either, I just need a clear sign from you guys so I don't
>> keep deimplementing and reimplementing this forever.
> 
> I would be for make it simple now and go with additional features later
> when there is a demand for them. Maybe we will have runtimg switch for
> user memory accounting as well one day.
> 

Since this would change a then established behavior, the same
discussions about compatibility we ever get to will rise. It is a pain
we'd better avoid if we can.

> But let's see what others think?
> 

Absolutely. Hello others, what do you think ?

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