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    SubjectRe: [RFC][PATCH] Cross Memory Attach
    On Wed, 15 Sep 2010 10:02:35 +0200
    Ingo Molnar <> wrote:
    > What did those OpenMPI facilities use before your patch - shared
    > memory or sockets?

    This comparison is against OpenMPI using the shared memory btl.

    > I have an observation about the interface:
    > A small detail: 'int flags' should probably be 'unsigned long flags'
    > - it leaves more space.


    > Also, note that there is a further performance optimization possible
    > here: if the other task's ->mm is the same as this task's (they share
    > the MM), then the copy can be done straight in this process context,
    > without GUP. User-space might not necessarily be aware of this so it
    > might make sense to express this special case in the kernel too.


    > More fundamentally, wouldnt it make sense to create an iovec
    > interface here? If the Gather(v) / Scatter(v) / AlltoAll(v) workloads
    > have any fragmentation on the user-space buffer side then the copy of
    > multiple areas could be done in a single syscall. (the MM lock has to
    > be touched only once, target task only be looked up only once, etc.)

    yes, I think so. Currently where I'm using the interface in OpenMPI I
    can't take advantage of this, but it could be changed in the future- and
    its likely other MPI's could take advantage of it already.

    > Plus, a small naming detail, shouldnt the naming be more IO like:
    > sys_process_vm_read()
    > sys_process_vm_write()

    Yes, that looks better to me. I really wasn't sure how to name them.



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