From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Prepare for the kernel to auto-migrate pages to other memory nodes
with a user defined node migration table. This allows creating single
migration target for each NUMA node to enable the kernel to do NUMA
page migrations instead of simply reclaiming colder pages. A node
with no target is a "terminal node", so reclaim acts normally there.
The migration target does not fundamentally _need_ to be a single node,
but this implementation starts there to limit complexity.
If you consider the migration path as a graph, cycles (loops) in the
graph are disallowed. This avoids wasting resources by constantly
migrating (A->B, B->A, A->B ...). The expectation is that cycles will
never be allowed.
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: osalvador <osalvador@xxxxxxx>
--
changes since 20200122:
* Make node_demotion[] __read_mostly
changes in July 2020:
- Remove loop from next_demotion_node() and get_online_mems().
This means that the node returned by next_demotion_node()
might now be offline, but the worst case is that the
allocation fails. That's fine since it is transient.
---
b/mm/migrate.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff -puN mm/migrate.c~0006-node-Define-and-export-memory-migration-path mm/migrate.c
--- a/mm/migrate.c~0006-node-Define-and-export-memory-migration-path 2021-03-04 15:35:51.353806441 -0800
+++ b/mm/migrate.c 2021-03-04 15:35:51.359806441 -0800
@@ -1157,6 +1157,23 @@ out:
return rc;
}
+static int node_demotion[MAX_NUMNODES] __read_mostly =
+ {[0 ... MAX_NUMNODES - 1] = NUMA_NO_NODE};
+
+/**
+ * next_demotion_node() - Get the next node in the demotion path
+ * @node: The starting node to lookup the next node
+ *
+ * @returns: node id for next memory node in the demotion path hierarchy
+ * from @node; NUMA_NO_NODE if @node is terminal. This does not keep
+ * @node online or guarantee that it *continues* to be the next demotion
+ * target.
+ */
+int next_demotion_node(int node)
+{
+ return node_demotion[node];
+}
+
/*
* Obtain the lock on page, remove all ptes and migrate the page
* to the newly allocated page in newpage.
_
