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    SubjectRe: [PATCH] Make CONFIG_MIGRATION available for s390
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    On Mon, 2008-07-07 at 10:09 -0500, Christoph Lameter wrote:
    > This will extend the number of pages that are migratable and lead to strange
    > semantics in the NUMA case. There suddenly vma_is migratable will forbid hotplug
    > to migrate certain pages.
    >
    > I think we need two functions:
    >
    > vma_migratable() General migratability
    >
    > vma_policy_migratable() Migratable under NUMA policies.

    Nothing will change here for the NUMA case, this is all about making it
    compile w/o NUMA and with MIGRATION. What new strange semantics do you mean?
    BTW, the latest patch in this thread will not touch vma_migratable() anymore,
    I haven't read your mail before, sorry.

    > That wont work since the migrate function takes a nodemask! The point of
    > the function is to move memory from node to node which is something that you
    > *cannot* do in a non NUMA configuration. So leave this chunk out.

    Right, but I noticed that this function definition was needed to make it
    compile with MIGRATION and w/o NUMA, although it would never be called in
    non-NUMA config.
    A better solution would probably be to put migrate_vmas(), the only caller
    of vm_ops->migrate(), inside '#ifdef CONFIG_NUMA', because it will only be
    called from NUMA-only mm/mempolicy.c. Does that sound reasonable?

    > Hmmm... Okay. I tried to make MIGRATION as independent of CONFIG_NUMA as possible so hopefully this will work.

    Umm, it doesn't compile with MIGRATION and w/o NUMA, which was the reason
    for this patch, because of the policy_zone reference in vma_migratable()
    and the missing vm_ops->migrate() function.

    Thanks,
    Gerald



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