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SubjectRe: [PATCH] Make GFP_DMA allocations w/o ZONE_DMA emit a warning instead of failing
On Fri, 10 Jun 2011, Russell King - ARM Linux wrote:

> > > > Should one submit a patch adding a warning to GFP_DMA allocations
> > > > w/o ZONE_DMA, or the idea of the original patch is wrong?
> > >
> > > Linus was far from impressed by the original commit, saying:
> > > | Using GFP_DMA is reasonable in a driver - on platforms where that
> > > | matters, it should allocate from the DMA zone, on platforms where it
> > > | doesn't matter it should be a no-op.
> > >
> > > So no, not even a warning.
> > >
> >
> > Any words of wisdom for users with CONFIG_ZONE_DMA=n that actually use
> > drivers where they need GFP_DMA? The page allocator should just silently
> > return memory from anywhere?
> See Linus' reply. I quote again "on platforms where it doesn't matter it
> should be a no-op". If _you_ have a problem with that _you_ need to
> discuss it with _Linus_, not me. I'm not going to be a middle-man sitting
> between two people with different opinions.

We're talking about two different things. Linus is saying that if GFP_DMA
should be a no-op if the hardware doesn't require DMA memory because the
kernel was correctly compiled without CONFIG_ZONE_DMA. I'm asking about a
kernel that was incorrectly compiled without CONFIG_ZONE_DMA and now we're
returning memory from anywhere even though we actually require GFP_DMA.

If you don't want to form an opinion of your own, then I have no problem
cc'ing Linus on it. I don't think he'd object to a

WARN_ON_ONCE(1, "%s (%d): allocating DMA memory without DMA support -- "
"enable CONFIG_ZONE_DMA if needed.\n",
current->comm, current->pid);

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