diff options
| -rw-r--r-- | mm/internal.h | 5 | ||||
| -rw-r--r-- | mm/migrate.c | 216 | ||||
| -rw-r--r-- | mm/page_alloc.c | 2 |
3 files changed, 222 insertions, 1 deletions
diff --git a/mm/internal.h b/mm/internal.h index 57e28261a3b1..cf3cb933eba3 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -543,12 +543,17 @@ static inline void mminit_validate_memmodel_limits(unsigned long *start_pfn, #ifdef CONFIG_NUMA extern int node_reclaim(struct pglist_data *, gfp_t, unsigned int); +extern int find_next_best_node(int node, nodemask_t *used_node_mask); #else static inline int node_reclaim(struct pglist_data *pgdat, gfp_t mask, unsigned int order) { return NODE_RECLAIM_NOSCAN; } +static inline int find_next_best_node(int node, nodemask_t *used_node_mask) +{ + return NUMA_NO_NODE; +} #endif extern int hwpoison_filter(struct page *p); diff --git a/mm/migrate.c b/mm/migrate.c index 7e240437e7d9..57aeb9b491da 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1099,6 +1099,80 @@ out: 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. @@ -2982,3 +3056,145 @@ void migrate_vma_finalize(struct migrate_vma *migrate) } 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(); +} diff --git a/mm/page_alloc.c b/mm/page_alloc.c index eaa936efad7e..cafdca874e0d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6157,7 +6157,7 @@ static int node_load[MAX_NUMNODES]; * * Return: node id of the found node or %NUMA_NO_NODE if no node is found. */ -static int find_next_best_node(int node, nodemask_t *used_node_mask) +int find_next_best_node(int node, nodemask_t *used_node_mask) { int n, val; int min_val = INT_MAX; |