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    SubjectRe: [PATCH v4 0/13] Uprobes v4
    * Srikar Dronamraju (srikar@linux.vnet.ibm.com) wrote:
    > > * Srikar Dronamraju (srikar@linux.vnet.ibm.com) wrote:
    > > > Uprobes Patches
    > > >
    > > > Changelog from v3:
    > > > - Reverted to background page replacement as suggested by Peter Zijlstra.
    > >
    > > Why ?
    > >
    > > I'm not sure we reached any concensus about the need for a background page
    > > replacement.
    > >
    > > Thanks,
    > >
    > > Mathieu
    > >
    >
    > I was tested with access_process_vm(previous patchset) and the current
    > (background page replacement) and the results are the same.
    >
    > However Peter Zijlstra's contention still stands that we might be
    > relying on a undocumented feature in the hardware

    The access_process_vm scheme is in many ways similar to what kprobes has been
    doing for years. So I would not rely on that as a primary argument against
    the access_process_vm approach.

    > and the flipping the
    > pages isnt that hard or expensive.
    >
    > Even Linus, (http://lkml.org/lkml/2010/1/27/87) had shown inclination
    > towards background page replacement.
    >
    > Also when uprobes implements global tracing support (i.e probing a
    > particular symbol in a dso across processes), it has to rely on
    > background page replacement.

    Ah OK. If you have to use page replacement for global tracing, I see that as a
    good argument for using page replacement everywhere.

    >
    > Hence I based this patchset on background page replacement rather than
    > on access_process_vm. Later On, if there is a consensus on using
    > access_process_vm, we can make the corresponding changes.

    Well, page replacement seems like a good way to support global tracing, so I
    doubt that we'll ever revert back to access_process_vm.

    Thanks,

    Mathieu

    >
    > --
    > Thanks and Regards
    > Srikar

    --
    Mathieu Desnoyers
    Operating System Efficiency R&D Consultant
    EfficiOS Inc.
    http://www.efficios.com


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