Messages in this thread Patch in this message | | | Subject | Re: [RFC PATCH v2] mm: migrate: Support multiple target nodes demotion | From | Baolin Wang <> | Date | Tue, 9 Nov 2021 17:54:58 +0800 |
| |
On 2021/11/9 15:53, Huang, Ying writes: > Baolin Wang <baolin.wang@linux.alibaba.com> writes: > >> We have some machines with multiple memory types like below, which >> have one fast (DRAM) memory node and two slow (persistent memory) memory >> nodes. According to current node demotion, if node 0 fills up, >> its memory should be migrated to node 1, when node 1 fills up, its >> memory will be migrated to node 2: node 0 -> node 1 -> node 2 ->stop. >> >> But this is not efficient and suitbale memory migration route >> for our machine with multiple slow memory nodes. Since the distance >> between node 0 to node 1 and node 0 to node 2 is equal, and memory >> migration between slow memory nodes will increase persistent memory >> bandwidth greatly, which will hurt the whole system's performance. >> >> Thus for this case, we can treat the slow memory node 1 and node 2 >> as a whole slow memory region, and we should migrate memory from >> node 0 to node 1 and node 2 if node 0 fills up. >> >> This patch changes the node_demotion data structure to support multiple >> target nodes, and establishes the migration path to support multiple >> target nodes with validating if the node distance is the best or not. >> >> available: 3 nodes (0-2) >> node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 >> node 0 size: 62153 MB >> node 0 free: 55135 MB >> node 1 cpus: >> node 1 size: 127007 MB >> node 1 free: 126930 MB >> node 2 cpus: >> node 2 size: 126968 MB >> node 2 free: 126878 MB >> node distances: >> node 0 1 2 >> 0: 10 20 20 >> 1: 20 10 20 >> 2: 20 20 10 >> >> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> >> --- >> Changes from RFC v1: >> - Re-define the node_demotion structure. >> - Set up multiple target nodes by validating the node distance. >> - Add more comments. >> --- >> mm/migrate.c | 132 +++++++++++++++++++++++++++++++++++++++++++---------------- >> 1 file changed, 96 insertions(+), 36 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index cf25b00..95f170d 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1119,12 +1119,25 @@ static int __unmap_and_move(struct page *page, struct page *newpage, >> * >> * 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 >> + * { nr=1, nodes[0]=1 }, // Node 0 migrates to 1 >> + * { nr=1, nodes[0]=2 }, // Node 1 migrates to 2 >> + * { nr=0, nodes[0]=-1 }, // Node 2 does not migrate >> + * { nr=1, nodes[0]=4 }, // Node 3 migrates to 4 >> + * { nr=1, nodes[0]=5 }, // Node 4 migrates to 5 >> + * { nr=0, nodes[0]=-1} // Node 5 does not migrate >> + * >> + * Moreover some systems may have multiple same class memory >> + * types. Suppose a system has one socket with 3 memory nodes, >> + * node 0 is fast memory type, and node 1/2 both are slow memory >> + * type, and the distance between fast memory node and slow >> + * memory node is same. So the migration path should be: >> + * >> + * 0 -> 1/2 -> stop >> + * >> + * This is represented in the node_demotion[] like this: >> + * { nr=2, {nodes[0]=1, nodes[1]=2} }, // Node 0 migrates to node 1 and node 2 >> + * { nr=0, nodes[0]=-1, }, // Node 1 dose not migrate >> + * { nr=0, nodes[0]=-1, }, // Node 2 does not migrate >> */ >> >> /* >> @@ -1135,8 +1148,13 @@ static int __unmap_and_move(struct page *page, struct page *newpage, >> * 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}; >> +#define DEMOTION_TARGET_NODES 15 >> +struct demotion_nodes { >> + unsigned short nr; >> + int nodes[DEMOTION_TARGET_NODES]; > > Why we cannot use "unsigned short" for nodes[]?
I think the default value of target node should be NUMA_NO_NODE(-1), so a signed type is more suitable. I can change to 'short' type.
> >> +}; >> + >> +static struct demotion_nodes node_demotion[MAX_NUMNODES] __read_mostly; >> >> /** >> * next_demotion_node() - Get the next node in the demotion path >> @@ -1149,7 +1167,9 @@ static int __unmap_and_move(struct page *page, struct page *newpage, >> */ >> int next_demotion_node(int node) >> { >> - int target; >> + struct demotion_nodes *current_node_demotion = &node_demotion[node]; >> + int target, i; >> + nodemask_t target_nodes = NODE_MASK_NONE; >> >> /* >> * node_demotion[] is updated without excluding this >> @@ -1161,9 +1181,21 @@ int next_demotion_node(int node) >> * node_demotion[] reads need to be consistent. >> */ >> rcu_read_lock(); >> - target = READ_ONCE(node_demotion[node]); >> + for (i = 0; i < DEMOTION_TARGET_NODES; i++) { >> + target = READ_ONCE(current_node_demotion->nodes[i]); >> + if (target == NUMA_NO_NODE) >> + break; >> + >> + node_set(target, target_nodes); > > Why do we need a nodemask? Why not just find a target node from > current_node_demotion->nodes[] randomly and directly?
I think nodemask is scalable in future if we want to add more requirements to select the target node if necessary. Anyway now I have no strong preference with the nodemask, and can change to select the target node randomly and directly, which are something like below.
+ target_nr = READ_ONCE(current_node_demotion->nr); + + if (target_nr == 0) { + target = NUMA_NO_NODE; + goto out; + } else if (target_nr == 1) { + index = 0; + } else { + /* + * If there are multiple target nodes, just select one + * target node randomly. + */ + index = get_random_int() % target_nr; + } + + target = READ_ONCE(current_node_demotion->nodes[index]);
> >> + } >> + >> rcu_read_unlock(); >> >> + if (nodes_empty(target_nodes)) >> + return NUMA_NO_NODE; >> + >> + /* TODO: Select a target node randomly */ >> + target = node_random(&target_nodes); >> return target; >> } >> >> @@ -2974,10 +3006,13 @@ void migrate_vma_finalize(struct migrate_vma *migrate) >> /* Disable reclaim-based migration. */ >> static void __disable_all_migrate_targets(void) >> { >> - int node; >> + int node, i; >> >> - for_each_online_node(node) >> - node_demotion[node] = NUMA_NO_NODE; >> + for_each_online_node(node) { >> + node_demotion[node].nr = 0; >> + for (i = 0; i < DEMOTION_TARGET_NODES; i++) >> + node_demotion[node].nodes[i] = NUMA_NO_NODE; >> + } >> } >> >> static void disable_all_migrate_targets(void) >> @@ -3004,26 +3039,34 @@ static void disable_all_migrate_targets(void) >> * 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) >> +static int establish_migrate_target(int node, nodemask_t *used, >> + int best_distance) >> { >> - int migration_target; >> + int migration_target, index, val; >> + struct demotion_nodes *current_node_demotion = &node_demotion[node]; >> + >> + migration_target = find_next_best_node(node, used); >> + if (migration_target == NUMA_NO_NODE) >> + return NUMA_NO_NODE; >> >> /* >> - * 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 the node has been set a migration target node before, >> + * which means it's the best distance between them. Still >> + * check if this node can be demoted to other target nodes >> + * if they have a same best distance. >> */ >> - if (node_demotion[node] != NUMA_NO_NODE) >> - return NUMA_NO_NODE; >> + if (best_distance != -1) { >> + val = node_distance(node, migration_target); >> + if (val > best_distance) >> + return NUMA_NO_NODE; >> + } >> >> - migration_target = find_next_best_node(node, used); >> - if (migration_target == NUMA_NO_NODE) >> + index = current_node_demotion->nr; >> + if (index >= DEMOTION_TARGET_NODES) > > I think we need WARN_ONCE() here, so we can increase > DEMOTION_TARGET_NODES if necessary.
Sure, will do. Thanks for your comments.
> >> return NUMA_NO_NODE; >> >> - node_demotion[node] = migration_target; >> + current_node_demotion->nodes[index] = migration_target; >> + current_node_demotion->nr++; >> >> return migration_target; >> } >> @@ -3039,7 +3082,9 @@ static int establish_migrate_target(int node, nodemask_t *used) >> * >> * 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. >> + * node1 migrates to can migrate to node0. Also one node can >> + * be migrated to multiple nodes if the target nodes all have >> + * a same best-distance against the source node. >> * >> * This function can run simultaneously with readers of >> * node_demotion[]. However, it can not run simultaneously >> @@ -3051,7 +3096,7 @@ 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; >> + int node, best_distance; >> >> /* >> * Avoid any oddities like cycles that could occur >> @@ -3080,18 +3125,33 @@ static void __set_migration_target_nodes(void) >> * 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; >> + for_each_node_mask(node, this_pass) { >> + best_distance = -1; >> >> /* >> - * 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'. >> + * Try to set up the migration path for the node, and the target >> + * migration nodes can be multiple, so doing a loop to find all >> + * the target nodes if they all have a best node distance. >> */ >> - node_set(target_node, next_pass); >> + do { >> + int target_node = >> + establish_migrate_target(node, &used_targets, >> + best_distance); >> + >> + if (target_node == NUMA_NO_NODE) >> + break; >> + >> + if (best_distance == -1) >> + best_distance = node_distance(node, target_node); >> + >> + /* >> + * 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); >> + } while (1); >> } >> /* >> * 'next_pass' contains nodes which became migration > > Best Regards, > Huang, Ying >
| |