[PATCH 4.14 097/183] powerpc/numa: Use ibm,max-associativity-domains to discover possible nodes

From: Greg Kroah-Hartman
Date: Wed Apr 25 2018 - 06:41:17 EST

4.14-stable review patch. If anyone has any objections, please let me know.


From: Michael Bringmann <mwb@xxxxxxxxxxxxxxxxxx>

[ 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

* 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@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Nathan Fontenot <nfont@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
arch/powerpc/mm/numa.c | 37 ++++++++++++++++++++++++++++++++++---
1 file changed, 34 insertions(+), 3 deletions(-)

--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -887,6 +887,34 @@ static void __init setup_node_data(int n
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);
+ }
+ }
+ of_node_put(rtas);
void __init initmem_init(void)
int nid, cpu;
@@ -900,12 +928,15 @@ void __init initmem_init(void)

- * 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;