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    SubjectRe: [patch] x86: allow ZONE_DMA to be configurable
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    > On Wed, 13 Oct 2010 17:15:04 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:
    >
    > > ZONE_DMA is unnecessary for a large number of machines that do not
    > > require addressing in the lower 16MB of memory because they do not use
    > > ISA devices with 16-bit address registers (plus one page byte register).
    > >
    > > This patch allows users to disable ZONE_DMA for x86 if they know they
    > > will not be using such devices with their kernel.
    > >
    > > This prevents the VM from unnecessarily reserving a ratio of memory
    > > (defaulting to 1/256th of system capacity) with lowmem_reserve_ratio
    > > for such allocations when it will never be used.
    > >
    >
    > I wonder how hard it would be to do this at runtime, probably with a
    > boot parameter.
    >
    > I'd be a little concerned at the effects of this on page reclaim and
    > the page allocator - it might expose weird pre-existing bugs or
    > inefficiencies. But we can cross that bridge when we fall off it, I
    > guess.

    In this case, completely ZONE disablling is not required. 16MB saving
    is not big matter. To prevent userland process use lower zone is necessary.

    I have such patch, because 32bit highmem system has similar requirement.
    (user process want to only use ZONE_HIGHMEM, otherwize ZONE_NORMAL easily
    exshost)

    I'll prepare to post them if necessary.






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