From: Keith Busch <[email protected]>
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 <[email protected]> Signed-off-by: Dave Hansen <[email protected]> --- 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) _
