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SubjectRe: [patch] x86: allow ZONE_DMA to be configurable
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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@google.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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