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    SubjectRe: [Intel IOMMU 06/10] Avoid memory allocation failures in dma map api calls
    On Wed, Jun 20, 2007 at 11:11:05PM -0700, Arjan van de Ven wrote:
    > Peter Zijlstra wrote:
    > >What I'm saying is that if you do use the reserves, you should ensure
    > >the use is bounded. I'm not seeing anything like that.
    >
    > each mapping takes at most 3 pages
    With 3 pages(3 level page table), IOMMU can map at
    most 2MB and each additional last level page helps
    map another 2MB. Again, the IOMMU driver re-uses the
    virtual address instead of giving contiguous virtual address
    which helps to keep the page table growth and helps
    reuse the same page table entries, in that sense we are
    bounded, again we are not sure how much IO will be in flight
    on a perticular system so as to reserve that many pages for
    IOMMU page table setup.

    -Anil
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