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SubjectRe: [patch] x86: allow ZONE_DMA to be configurable
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

WARN_ON_ONCE(gfp_mask & __GFP_DMA);

in the page allocator.

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