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Subject[PATCH 1/4] node: Define and export memory migration path
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From: Keith Busch <keith.busch@intel.com>

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, and this rule is enforced if the user tries to make
such a cycle.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
---

b/drivers/base/node.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++++
b/include/linux/node.h | 6 ++++
2 files changed, 79 insertions(+)

diff -puN drivers/base/node.c~0003-node-Define-and-export-memory-migration-path drivers/base/node.c
--- a/drivers/base/node.c~0003-node-Define-and-export-memory-migration-path 2019-10-16 15:06:55.895952599 -0700
+++ b/drivers/base/node.c 2019-10-16 15:06:55.902952599 -0700
@@ -101,6 +101,10 @@ static const struct attribute_group *nod
NULL,
};

+#define TERMINAL_NODE -1
+static int node_migration[MAX_NUMNODES] = {[0 ... MAX_NUMNODES - 1] = TERMINAL_NODE};
+static DEFINE_SPINLOCK(node_migration_lock);
+
static void node_remove_accesses(struct node *node)
{
struct node_access_nodes *c, *cnext;
@@ -530,6 +534,74 @@ static ssize_t node_read_distance(struct
}
static DEVICE_ATTR(distance, S_IRUGO, node_read_distance, NULL);

+static ssize_t migration_path_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ return sprintf(buf, "%d\n", node_migration[dev->id]);
+}
+
+static ssize_t migration_path_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ int i, err, nid = dev->id;
+ nodemask_t visited = NODE_MASK_NONE;
+ long next;
+
+ err = kstrtol(buf, 0, &next);
+ if (err)
+ return -EINVAL;
+
+ if (next < 0) {
+ spin_lock(&node_migration_lock);
+ WRITE_ONCE(node_migration[nid], TERMINAL_NODE);
+ spin_unlock(&node_migration_lock);
+ return count;
+ }
+ if (next >= MAX_NUMNODES || !node_online(next))
+ return -EINVAL;
+
+ /*
+ * Follow the entire migration path from 'nid' through the point where
+ * we hit a TERMINAL_NODE.
+ *
+ * Don't allow loops migration cycles in the path.
+ */
+ node_set(nid, visited);
+ spin_lock(&node_migration_lock);
+ for (i = next; node_migration[i] != TERMINAL_NODE;
+ i = node_migration[i]) {
+ /* Fail if we have visited this node already */
+ if (node_test_and_set(i, visited)) {
+ spin_unlock(&node_migration_lock);
+ return -EINVAL;
+ }
+ }
+ WRITE_ONCE(node_migration[nid], next);
+ spin_unlock(&node_migration_lock);
+
+ return count;
+}
+static DEVICE_ATTR_RW(migration_path);
+
+/**
+ * next_migration_node() - Get the next node in the migration path
+ * @current_node: The starting node to lookup the next node
+ *
+ * @returns: node id for next memory node in the migration path hierarchy from
+ * @current_node; -1 if @current_node is terminal or its migration
+ * node is not online.
+ */
+int next_migration_node(int current_node)
+{
+ int nid = READ_ONCE(node_migration[current_node]);
+
+ if (nid >= 0 && node_online(nid))
+ return nid;
+ return TERMINAL_NODE;
+}
+
static struct attribute *node_dev_attrs[] = {
&dev_attr_cpumap.attr,
&dev_attr_cpulist.attr,
@@ -537,6 +609,7 @@ static struct attribute *node_dev_attrs[
&dev_attr_numastat.attr,
&dev_attr_distance.attr,
&dev_attr_vmstat.attr,
+ &dev_attr_migration_path.attr,
NULL
};
ATTRIBUTE_GROUPS(node_dev);
diff -puN include/linux/node.h~0003-node-Define-and-export-memory-migration-path include/linux/node.h
--- a/include/linux/node.h~0003-node-Define-and-export-memory-migration-path 2019-10-16 15:06:55.898952599 -0700
+++ b/include/linux/node.h 2019-10-16 15:06:55.902952599 -0700
@@ -134,6 +134,7 @@ static inline int register_one_node(int
return error;
}

+extern int next_migration_node(int current_node);
extern void unregister_one_node(int nid);
extern int register_cpu_under_node(unsigned int cpu, unsigned int nid);
extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid);
@@ -186,6 +187,11 @@ static inline void register_hugetlbfs_wi
node_registration_func_t unreg)
{
}
+
+static inline int next_migration_node(int current_node)
+{
+ return -1;
+}
#endif

#define to_node(device) container_of(device, struct node, dev)
_
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