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nvme-multipath: find NUMA path only for online numa-node

Chris Leech requested to merge cleech/centos-stream-9:cs9-rhel-40088 into main

JIRA: https://issues.redhat.com/browse/RHEL-40088

commit d3a043733f25d743f3aa617c7f82dbcb5ee2211a
Author: Nilay Shroff <nilay@linux.ibm.com>
Date:   Thu May 16 17:43:51 2024 +0530

    nvme-multipath: find NUMA path only for online numa-node

    In current native multipath design when a shared namespace is created,
    we loop through each possible numa-node, calculate the NUMA distance of
    that node from each nvme controller and then cache the optimal IO path
    for future reference while sending IO. The issue with this design is that
    we may refer to the NUMA distance table for an offline node which may not
    be populated at the time and so we may inadvertently end up finding and
    caching a non-optimal path for IO. Then latter when the corresponding
    numa-node becomes online and hence the NUMA distance table entry for that
    node is created, ideally we should re-calculate the multipath node distance
    for the newly added node however that doesn't happen unless we rescan/reset
    the controller. So essentially, we may keep using non-optimal IO path for a
    node which is made online after namespace is created.
    This patch helps fix this issue ensuring that when a shared namespace is
    created, we calculate the multipath node distance for each online numa-node
    instead of each possible numa-node. Then latter when a node becomes online
    and we receive any IO on that newly added node, we would calculate the
    multipath node distance for newly added node but this time NUMA distance
    table would have been already populated for newly added node. Hence we
    would be able to correctly calculate the multipath node distance and choose
    the optimal path for the IO.

    Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Keith Busch <kbusch@kernel.org>

Signed-off-by: Chris Leech cleech@redhat.com

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