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

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Message-ID: <4CB688F4.9040706@zytor.com>
Date:	Wed, 13 Oct 2010 21:37:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Casey Dahlin <cdahlin@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] x86: allow ZONE_DMA to be configurable

On 10/13/2010 06:48 PM, David Rientjes wrote:
> On Wed, 13 Oct 2010, H. Peter Anvin wrote:
> 
>> And the value of those additional options is what?  I'd consider adding 
>> this to the sewer pit called CONFIG_EMBEDDED (with a BUG_ON, not a 
>> warning... sheesh)
> 
> BUG_ON() could panic the machine which would be rather unfortunate if we 
> simply tried to load a driver that the kernel no longer supports because 
> it doesn't have DMA.  A WARN_ON() seems much more appropriate to identify 
> what the problem was.  It's not a fatal condition.
> 
>> but only if there is any demonstrable value other 
>> than a trivial amount of code (kilobytes?) in exchange for a bunch of 
>> crap #ifdef.
>>
> 
> The data savings is about 1% and the text savings is about 0.1% with all 
> three options disabled:
> 
> 7922297	1245500	 989600	10157397	 9afd55	vmlinux.before
> 7914674	1232700	 989472	10136846	 9aad0e	vmlinux.after
> 
> This is the only #ifdef necessary to make CONFIG_ZONE_DMA=n compile and 
> CONFIG_GENERIC_ISA_DMA=n would require two additional #ifdefs 
> (CONFIG_ISA_DMA_API=n would require none).  We carry this patch 
> internally, so it would be trivial to send follow-up patches that do that 
> if this patch is merged.

I guess that qualifies (barely, arguably, but let's not go there) as
something that would be able to be carried under CONFIG_EMBEDDED
(certainly not without).

However, I'd like to have the whole thing as a complete patch series.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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