Re: [RFC 2.6.11-rc2-mm2 0/7] mm: manual page migration -- overview II

From: Andi Kleen (ak_at_suse.de)
Date: 02/21/05

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    Date:	Mon, 21 Feb 2005 13:10:11 +0100
To: Ray Bryant <raybry@sgi.com>

    On Mon, Feb 21, 2005 at 02:42:16AM -0600, Ray Bryant wrote:
    > All,
    >
    > Just an update on the idea of migrating a process without suspending
    > it.
    >
    > The hard part of the problem here is to make sure that the page_migrate()
    > system call sees all of the pages to migrate. If the process that is
    > being migrated can still allocate pages, then the page_migrate() call
    > may miss some of the pages.

    I would do an easy 95% solution:

    When process has default process policy set temporarily a prefered policy
    with the new node

    [this won't work with multiple nodes though, so you have to decide on one
    or stop the process if that is unacceptable]

    >
    > One way to solve this problem is to force the process to start allocating
    > pages on the new nodes before calling page_migrate(). There are a couple
    > of subcases:
    >
    > (1) For memory mapped files with a non-DEFAULT associated memory policy,
    > one can use mbind() to fixup the memory policy. (This assumes the
    > Steve Longerbeam patches are applied, as I understand things).

    I would just ignore them. If user space wants it can handle it,
    but it's probably not worth it.

    > (1) could be handled as part of the page_migrate() system call --
    > make one pass through the address space searching for mempolicy()
    > data structures, and updating them as necessary. Then make a second
    > pass through and do the migrations. Any new allocations will then
    > be done under the new mempolicy, so they won't be missed. But this
    > still gets us into trouble if the old and new node lists are not
    > disjoint.

    I wouldn't bother fixing up VMA policies.

    > This doesn't handle anonymous memory or mapped files associated with
    > the DEFAULT policy. A way around that would be to add a target cpu_id

    [...]

    I would set temporarily a prefered policy as mentioned above.

    That only handles a single node, but you solution is not better.

    -Andi
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