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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

    #ifndef CONFIG_ZONE_DMA
    WARN_ON_ONCE(gfp_mask & __GFP_DMA);
    #endif

    in the page allocator.


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