return rc;
}
+
+/*
+ * node_demotion[] example:
+ *
+ * Consider a system with two sockets. Each socket has
+ * three classes of memory attached: fast, medium and slow.
+ * Each memory class is placed in its own NUMA node. The
+ * CPUs are placed in the node with the "fast" memory. The
+ * 6 NUMA nodes (0-5) might be split among the sockets like
+ * this:
+ *
+ * Socket A: 0, 1, 2
+ * Socket B: 3, 4, 5
+ *
+ * When Node 0 fills up, its memory should be migrated to
+ * Node 1. When Node 1 fills up, it should be migrated to
+ * Node 2. The migration path start on the nodes with the
+ * processors (since allocations default to this node) and
+ * fast memory, progress through medium and end with the
+ * slow memory:
+ *
+ * 0 -> 1 -> 2 -> stop
+ * 3 -> 4 -> 5 -> stop
+ *
+ * This is represented in the node_demotion[] like this:
+ *
+ * { 1, // Node 0 migrates to 1
+ * 2, // Node 1 migrates to 2
+ * -1, // Node 2 does not migrate
+ * 4, // Node 3 migrates to 4
+ * 5, // Node 4 migrates to 5
+ * -1} // Node 5 does not migrate
+ */
+
+/*
+ * Writes to this array occur without locking. Cycles are
+ * not allowed: Node X demotes to Y which demotes to X...
+ *
+ * If multiple reads are performed, a single rcu_read_lock()
+ * must be held over all reads to ensure that no cycles are
+ * observed.
+ */
+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)
+{
+ int target;
+
+ /*
+ * node_demotion[] is updated without excluding this
+ * function from running. RCU doesn't provide any
+ * compiler barriers, so the READ_ONCE() is required
+ * to avoid compiler reordering or read merging.
+ *
+ * Make sure to use RCU over entire code blocks if
+ * node_demotion[] reads need to be consistent.
+ */
+ rcu_read_lock();
+ target = READ_ONCE(node_demotion[node]);
+ rcu_read_unlock();
+
+ return target;
+}
+
/*
* Obtain the lock on page, remove all ptes and migrate the page
* to the newly allocated page in newpage.
}
EXPORT_SYMBOL(migrate_vma_finalize);
#endif /* CONFIG_DEVICE_PRIVATE */
+
+/* Disable reclaim-based migration. */
+static void __disable_all_migrate_targets(void)
+{
+ int node;
+
+ for_each_online_node(node)
+ node_demotion[node] = NUMA_NO_NODE;
+}
+
+static void disable_all_migrate_targets(void)
+{
+ __disable_all_migrate_targets();
+
+ /*
+ * Ensure that the "disable" is visible across the system.
+ * Readers will see either a combination of before+disable
+ * state or disable+after. They will never see before and
+ * after state together.
+ *
+ * The before+after state together might have cycles and
+ * could cause readers to do things like loop until this
+ * function finishes. This ensures they can only see a
+ * single "bad" read and would, for instance, only loop
+ * once.
+ */
+ synchronize_rcu();
+}
+
+/*
+ * Find an automatic demotion target for 'node'.
+ * Failing here is OK. It might just indicate
+ * being at the end of a chain.
+ */
+static int establish_migrate_target(int node, nodemask_t *used)
+{
+ int migration_target;
+
+ /*
+ * Can not set a migration target on a
+ * node with it already set.
+ *
+ * No need for READ_ONCE() here since this
+ * in the write path for node_demotion[].
+ * This should be the only thread writing.
+ */
+ if (node_demotion[node] != NUMA_NO_NODE)
+ return NUMA_NO_NODE;
+
+ migration_target = find_next_best_node(node, used);
+ if (migration_target == NUMA_NO_NODE)
+ return NUMA_NO_NODE;
+
+ node_demotion[node] = migration_target;
+
+ return migration_target;
+}
+
+/*
+ * When memory fills up on a node, memory contents can be
+ * automatically migrated to another node instead of
+ * discarded at reclaim.
+ *
+ * Establish a "migration path" which will start at nodes
+ * with CPUs and will follow the priorities used to build the
+ * page allocator zonelists.
+ *
+ * The difference here is that cycles must be avoided. If
+ * node0 migrates to node1, then neither node1, nor anything
+ * node1 migrates to can migrate to node0.
+ *
+ * This function can run simultaneously with readers of
+ * node_demotion[]. However, it can not run simultaneously
+ * with itself. Exclusion is provided by memory hotplug events
+ * being single-threaded.
+ */
+static void __set_migration_target_nodes(void)
+{
+ nodemask_t next_pass = NODE_MASK_NONE;
+ nodemask_t this_pass = NODE_MASK_NONE;
+ nodemask_t used_targets = NODE_MASK_NONE;
+ int node;
+
+ /*
+ * Avoid any oddities like cycles that could occur
+ * from changes in the topology. This will leave
+ * a momentary gap when migration is disabled.
+ */
+ disable_all_migrate_targets();
+
+ /*
+ * Allocations go close to CPUs, first. Assume that
+ * the migration path starts at the nodes with CPUs.
+ */
+ next_pass = node_states[N_CPU];
+again:
+ this_pass = next_pass;
+ next_pass = NODE_MASK_NONE;
+ /*
+ * To avoid cycles in the migration "graph", ensure
+ * that migration sources are not future targets by
+ * setting them in 'used_targets'. Do this only
+ * once per pass so that multiple source nodes can
+ * share a target node.
+ *
+ * 'used_targets' will become unavailable in future
+ * passes. This limits some opportunities for
+ * multiple source nodes to share a destination.
+ */
+ nodes_or(used_targets, used_targets, this_pass);
+ for_each_node_mask(node, this_pass) {
+ int target_node = establish_migrate_target(node, &used_targets);
+
+ if (target_node == NUMA_NO_NODE)
+ continue;
+
+ /*
+ * Visit targets from this pass in the next pass.
+ * Eventually, every node will have been part of
+ * a pass, and will become set in 'used_targets'.
+ */
+ node_set(target_node, next_pass);
+ }
+ /*
+ * 'next_pass' contains nodes which became migration
+ * targets in this pass. Make additional passes until
+ * no more migrations targets are available.
+ */
+ if (!nodes_empty(next_pass))
+ goto again;
+}
+
+/*
+ * For callers that do not hold get_online_mems() already.
+ */
+__maybe_unused // <- temporay to prevent warnings during bisects
+static void set_migration_target_nodes(void)
+{
+ get_online_mems();
+ __set_migration_target_nodes();
+ put_online_mems();
+}
projects / linux-2.6-microblaze.git / blobdiff