linux-kernel - Re: [PATCH] Document huge memory/cache overhead of memory controller in Kconfig

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Message-ID: <47BC5211.6030102@linux.vnet.ibm.com>
Date:	Wed, 20 Feb 2008 21:45:13 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	John Stoffel <john@...ffel.org>
CC:	Jan Engelhardt <jengelh@...putergmbh.de>,
	Andi Kleen <andi@...stfloor.org>, akpm@...l.org,
	torvalds@...l.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] Document huge memory/cache overhead of memory controller
 in Kconfig

John Stoffel wrote:
>>>>>> "Jan" == Jan Engelhardt <jengelh@...putergmbh.de> writes:
> 
> Jan> On Feb 20 2008 20:50, Balbir Singh wrote:
>>> John Stoffel wrote:
>>>> I know this is a pedantic comment, but why the heck is it called such
>>>> a generic term as "Memory Controller" which doesn't give any
>>>> indication of what it does.
>>>>
>>>> Shouldn't it be something like "Memory Quota Controller", or "Memory
>>>> Limits Controller"?
>>> It's called the memory controller since it controls the amount of
>>> memory that a user can allocate (via limits). The generic term for
>>> any resource manager plugged into cgroups is a controller.
> 
> Jan> For ordinary desktop people, memory controller is what developers
> Jan> know as MMU or sometimes even some other mysterious piece of
> Jan> silicon inside the heavy box.
> 
> That's what was confusing me at first.  I was wondering why we needed
> a memory controller when we already had one in Linux!  
> 
> Also, controlling a resource is more a matter of limits or quotas, not
> controls.  Well, I'll actually back off on that, since controls does
> have a history in other industries.  
> 
> But for computers, limits is an expected and understood term, and for
> filesystems it's quotas.  So in this case, I *still* think you should
> be using the term "Memory Quota Controller" instead.  It just makes it
> clearer to a larger audience what you mean.
> 

Memory Quota sounds very confusing to me. Usually a quota implies limits, but in
a true framework, one can also implement guarantees and shares.

>>> If you look through some of the references in the document, we've
>>> listed our plans to support other categories of memory as well.
>>> Hence it's called a memory controller
>>>
>>>> Also, the Kconfig name "CGROUP_MEM_CONT" is just wrong, it should
>>>> be "CGROUP_MEM_CONTROLLER", just spell it out so it's clear what's
>>>> up.
> 
>>> This has some history as well. Control groups was called containers
>>> earlier. That way a name like CGROUP_MEM_CONT could stand for
>>> cgroup memory container or cgroup memory controller.
> 
> Jan> CONT is shorthand for "continue" ;-) (SIGCONT, f.ex.), ctrl or
> Jan> ctrlr it is for controllers (comes from Solaris iirc.)
> 
> Right, CTLR would be more regular shorthand for CONTROLLER.  
> 
> Basically, I think you're overloading a commonly used term for your
> own uses and when it's exposed to regular users, it will cause
> confusion.
> 

OK, I'll queue a patch and try to explain various terms used by resource management.

> Thanks,
> John


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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