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    SubjectRe: problem in follow_hugetlb_page on ppc64 architecture with get_user_pages
    On Tue, Nov 06, 2007 at 04:06:04PM +0100, Hoang-Nam Nguyen wrote:
    > Hello Roland!
    > > We currently see this when testing Infiniband on ppc64 with ehca +
    > > hugetlbfs.
    > > From reading the code this should also be an issue on other architectures.
    > > Roland, Adam, are you aware of anything in this area with mellanox
    > > Infiniband cards or other usages with I/O adapters?
    > Below is a testcase demonstrating this problem. You need to install
    > and run it as below:
    > HUGETLB_MORECORE=yes ./hugetlb_ibtest 100
    > This testcase does the following steps (high level desc):
    > 1. malloc two buffers each of 100MB for send and recv
    > 2. register them as memory regions
    > 3. create queue pair QP
    > 4. send data in send buffer using QP to itself (target is then recv buffer)
    > 5. compare those buffers content
    > It runs fine without libhugetlbsf. If you call it with libhugetlbfs as
    > above, step 5 will fail. If you do memset() of the buffers before step 2
    > (register mr), then it runs without errors.
    > It appears that hugetlb_cow() is called when first write access is performed
    > after mrs have been registered. That means the testcase is seeing other pages
    > than the ones registered to the adapter...
    > I was able reproduce this with mthca on 2.6.23/ppc64 and fc6/intel.

    We should cut this down to the bare necessary and fold it into the
    libhugetlbfs testsuite.

    David Gibson | I'll have my music baroque, and my code
    david AT | minimalist, thank you. NOT _the_ _other_
    | _way_ _around_!
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