linux-kernel - Re: [patch] x86: allow ZONE

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Message-ID: <alpine.DEB.2.00.1010150154510.8103@chino.kir.corp.google.com>
Date:	Fri, 15 Oct 2010 02:05:36 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Casey Dahlin <cdahlin@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] x86: allow ZONE_DMA to be configurable

On Fri, 15 Oct 2010, Ingo Molnar wrote:

> Also, historically we have not been moving kconfig variables in and out 
> of CONFIG_EMBEDDED all that often for this to be an issue in the future.
> 

There are also kconfig options that depend on EMBEDDED that are actually 
for embedded or very small systems; the most obvious example that comes to 
mind is SLOB.  Simply doing an s/EMBEDDED/EXPERT/ conversion seems 
appropriate given the semantics for the option that Peter gave, but there 
are exceptions that will need to be identified, and I think SLOB is one of 
them.

I don't think we need a kconfig _dependency_ that exists solely to 
identify other config options for a specific field of hardware, but then 
we leave a burden for those users to identify the correct options that 
they need for their configurations that was, I'm assuming, the original 
intent of CONFIG_EMBEDDED in the first place.  So perhaps we can allow an 
option for small embedded systems that can "select" other options when 
enabled but don't have strict "depends" requirements?

I had a thread with Matt Mackall about a year and a half ago on LKML about 
the meaning of CONFIG_EMBEDDED and its use for the SLOB allocator; it 
would be much better for us to identify systems with memory limitations 
that strive to reduce footprint as much as possible to automatically 
select certain options over others.  I believe we talked about SLOB being 
the default for systems with under 16MB of memory, but we have limited 
ability to identify that for the user.
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