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

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Date:	Wed, 20 Feb 2008 11:10:59 -0500
From:	"John Stoffel" <john@...ffel.org>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
Cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	John Stoffel <john@...ffel.org>,
	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

>>>>> "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.

>> 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.

Thanks,
John
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