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

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Date:	Wed, 13 Oct 2010 19:38:03 -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

How do you know it is not a fatal condition?

"David Rientjes" <rientjes@...gle.com> 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.

-- 
Sent from my mobile phone.  Please pardon any lack of formatting.
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