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    Subject[PATCH AUTOSEL for 4.14 085/161] powerpc/numa: Use ibm,max-associativity-domains to discover possible nodes
    Date
    From: Michael Bringmann <mwb@linux.vnet.ibm.com>

    [ Upstream commit a346137e9142b039fd13af2e59696e3d40c487ef ]

    On powerpc systems which allow 'hot-add' of CPU or memory resources,
    it may occur that the new resources are to be inserted into nodes that
    were not used for these resources at bootup. In the kernel, any node
    that is used must be defined and initialized. These empty nodes may
    occur when,

    * Dedicated vs. shared resources. Shared resources require information
    such as the VPHN hcall for CPU assignment to nodes. Associativity
    decisions made based on dedicated resource rules, such as
    associativity properties in the device tree, may vary from decisions
    made using the values returned by the VPHN hcall.

    * memoryless nodes at boot. Nodes need to be defined as 'possible' at
    boot for operation with other code modules. Previously, the powerpc
    code would limit the set of possible nodes to those which have
    memory assigned at boot, and were thus online. Subsequent add/remove
    of CPUs or memory would only work with this subset of possible
    nodes.

    * memoryless nodes with CPUs at boot. Due to the previous restriction
    on nodes, nodes that had CPUs but no memory were being collapsed
    into other nodes that did have memory at boot. In practice this
    meant that the node assignment presented by the runtime kernel
    differed from the affinity and associativity attributes presented by
    the device tree or VPHN hcalls. Nodes that might be known to the
    pHyp were not 'possible' in the runtime kernel because they did not
    have memory at boot.

    This patch ensures that sufficient nodes are defined to support
    configuration requirements after boot, as well as at boot. This patch
    set fixes a couple of problems.

    * Nodes known to powerpc to be memoryless at boot, but to have CPUs in
    them are allowed to be 'possible' and 'online'. Memory allocations
    for those nodes are taken from another node that does have memory
    until and if memory is hot-added to the node. * Nodes which have no
    resources assigned at boot, but which may still be referenced
    subsequently by affinity or associativity attributes, are kept in
    the list of 'possible' nodes for powerpc. Hot-add of memory or CPUs
    to the system can reference these nodes and bring them online
    instead of redirecting to one of the set of nodes that were known to
    have memory at boot.

    This patch extracts the value of the lowest domain level (number of
    allocable resources) from the device tree property
    "ibm,max-associativity-domains" to use as the maximum number of nodes
    to setup as possibly available in the system. This new setting will
    override the instruction:

    nodes_and(node_possible_map, node_possible_map, node_online_map);

    presently seen in the function arch/powerpc/mm/numa.c:initmem_init().

    If the "ibm,max-associativity-domains" property is not present at
    boot, no operation will be performed to define or enable additional
    nodes, or enable the above 'nodes_and()'.

    Signed-off-by: Michael Bringmann <mwb@linux.vnet.ibm.com>
    Reviewed-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    arch/powerpc/mm/numa.c | 37 ++++++++++++++++++++++++++++++++++---
    1 file changed, 34 insertions(+), 3 deletions(-)

    diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
    index a81279249bfb..0356c6cceff7 100644
    --- a/arch/powerpc/mm/numa.c
    +++ b/arch/powerpc/mm/numa.c
    @@ -887,6 +887,34 @@ static void __init setup_node_data(int nid, u64 start_pfn, u64 end_pfn)
    NODE_DATA(nid)->node_spanned_pages = spanned_pages;
    }

    +static void __init find_possible_nodes(void)
    +{
    + struct device_node *rtas;
    + u32 numnodes, i;
    +
    + if (min_common_depth <= 0)
    + return;
    +
    + rtas = of_find_node_by_path("/rtas");
    + if (!rtas)
    + return;
    +
    + if (of_property_read_u32_index(rtas,
    + "ibm,max-associativity-domains",
    + min_common_depth, &numnodes))
    + goto out;
    +
    + for (i = 0; i < numnodes; i++) {
    + if (!node_possible(i)) {
    + setup_node_data(i, 0, 0);
    + node_set(i, node_possible_map);
    + }
    + }
    +
    +out:
    + of_node_put(rtas);
    +}
    +
    void __init initmem_init(void)
    {
    int nid, cpu;
    @@ -900,12 +928,15 @@ void __init initmem_init(void)
    memblock_dump_all();

    /*
    - * Reduce the possible NUMA nodes to the online NUMA nodes,
    - * since we do not support node hotplug. This ensures that we
    - * lower the maximum NUMA node ID to what is actually present.
    + * Modify the set of possible NUMA nodes to reflect information
    + * available about the set of online nodes, and the set of nodes
    + * that we expect to make use of for this platform's affinity
    + * calculations.
    */
    nodes_and(node_possible_map, node_possible_map, node_online_map);

    + find_possible_nodes();
    +
    for_each_online_node(nid) {
    unsigned long start_pfn, end_pfn;

    --
    2.15.1
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