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    SubjectRe: [PATCH] Make GFP_DMA allocations w/o ZONE_DMA emit a warning instead of failing
    On Fri, Jun 10, 2011 at 03:01:15PM -0700, David Rientjes wrote:
    > On Fri, 10 Jun 2011, Russell King - ARM Linux wrote:
    > > 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.

    How do you distinguish between the two states? Answer: you can't.

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

    I think I've made my position in this fairly clear with our previous
    discussions on this. The fact of the matter is that there are some
    drivers which use GFP_DMA because they need that on _some_ platforms
    but not all.

    Not all platforms are _broken_ with respect to DMA, and those which
    aren't broken don't provide a DMA zone.

    Therefore, it is _perfectly_ _legal_ to honor a GFP_DMA allocation on
    a kernel without CONFIG_ZONE_DMA set.

    That position appears to be reflected by Linus' response, so

    > I don't think he'd object to a
    > #ifndef CONFIG_ZONE_DMA
    > WARN_ON_ONCE(1, "%s (%d): allocating DMA memory without DMA support -- "
    > "enable CONFIG_ZONE_DMA if needed.\n",
    > current->comm, current->pid);
    > #endif

    I think he will definitely object to this on the grounds that its
    adding useless noise for conditions which are _perfectly_ _valid_.

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