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

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Date:	Wed, 13 Oct 2010 18:21:48 -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

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) but only if there is any demonstrable value other than a trivial amount of code (kilobytes?) in exchange for a bunch of crap #ifdef.

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

>On Wed, 13 Oct 2010, H. Peter Anvin wrote:
>
>> > You can already set the lowmem_reserve_ratio via 
>> > /proc/sys/vm/lowmem_reserve_ratio.
>> 
>> And why is it then so hard to put in a single line in /etc/sysctl.conf
>> for you?
>> 
>
>Because disabling CONFIG_ZONE_DMA allows for additional extensions: 
>disabling CONFIG_GENERIC_ISA_DMA and CONFIG_ISA_DMA_API.  We've also run 
>for a couple years without those.
>
>> > We've run without ZONE_DMA for a couple years because we don't have such 
>> > hardware limitations and would appreciate the ability to disable it with a 
>> > config option rather than hacking the kernel to get it to compile.  I'm 
>> > sure Casey would as well as you can see in the thread "A question about 
>> > ZONE_DMA".
>> > 
>> > I don't see the harm in being able to conveniently disable the zone if you 
>> > know what you're doing.
>> 
>> There are going to be a lot of very strange bug reports as a result.
>> 
>
>We have config options all over the kernel that change the behavior of 
>syscalls without worrying about bug reports popping up from users who 
>knowingly have disabled the option, I don't see this as being any 
>different.  If you're concerned about, we could add a
>
>#ifndef CONFIG_ZONE_DMA
>	WARN_ON_ONCE(gfp_mask & __GFP_DMA);
>#endif
>
>in the page allocator.

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