From: Huang Ying <ying.huang@xxxxxxxxx> Subject: mm/migrate: move node demotion code to near its user Now, node_demotion and next_demotion_node() are placed between __unmap_and_move() and unmap_and_move(). This hurts code readability. So move them near their users in the file. There's no functionality change in this patch. Link: https://lkml.kernel.org/r/20211206031227.3323097-1-ying.huang@xxxxxxxxx Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> Reviewed-by: Yang Shi <shy828301@xxxxxxxxx> Reviewed-by: Wei Xu <weixugc@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Greg Thelen <gthelen@xxxxxxxxxx> Cc: Keith Busch <kbusch@xxxxxxxxxx> Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/migrate.c | 265 ++++++++++++++++++++++++------------------------- 1 file changed, 132 insertions(+), 133 deletions(-) --- a/mm/migrate.c~mm-migrate-move-node-demotion-code-to-near-its-user +++ a/mm/migrate.c @@ -1093,139 +1093,6 @@ 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: - * - * { 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 slow memory nodes. - * 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 - */ - -/* - * 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. - */ -#define DEFAULT_DEMOTION_TARGET_NODES 15 - -#if MAX_NUMNODES < DEFAULT_DEMOTION_TARGET_NODES -#define DEMOTION_TARGET_NODES (MAX_NUMNODES - 1) -#else -#define DEMOTION_TARGET_NODES DEFAULT_DEMOTION_TARGET_NODES -#endif - -struct demotion_nodes { - unsigned short nr; - short nodes[DEMOTION_TARGET_NODES]; -}; - -static struct demotion_nodes *node_demotion __read_mostly; - -/** - * next_demotion_node() - Get the next node in the demotion path - * @node: The starting node to lookup the next node - * - * Return: 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) -{ - struct demotion_nodes *nd; - unsigned short target_nr, index; - int target; - - if (!node_demotion) - return NUMA_NO_NODE; - - nd = &node_demotion[node]; - - /* - * 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_nr = READ_ONCE(nd->nr); - - switch (target_nr) { - case 0: - target = NUMA_NO_NODE; - goto out; - case 1: - index = 0; - break; - default: - /* - * If there are multiple target nodes, just select one - * target node randomly. - * - * In addition, we can also use round-robin to select - * target node, but we should introduce another variable - * for node_demotion[] to record last selected target node, - * that may cause cache ping-pong due to the changing of - * last target node. Or introducing per-cpu data to avoid - * caching issue, which seems more complicated. So selecting - * target node randomly seems better until now. - */ - index = get_random_int() % target_nr; - break; - } - - target = READ_ONCE(nd->nodes[index]); - -out: - rcu_read_unlock(); - return target; -} - /* * Obtain the lock on page, remove all ptes and migrate the page * to the newly allocated page in newpage. @@ -3059,6 +2926,138 @@ void migrate_vma_finalize(struct migrate EXPORT_SYMBOL(migrate_vma_finalize); #endif /* CONFIG_DEVICE_PRIVATE */ +/* + * 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: + * + * { 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 slow memory nodes. + * 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 + */ + +/* + * 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. + */ +#define DEFAULT_DEMOTION_TARGET_NODES 15 + +#if MAX_NUMNODES < DEFAULT_DEMOTION_TARGET_NODES +#define DEMOTION_TARGET_NODES (MAX_NUMNODES - 1) +#else +#define DEMOTION_TARGET_NODES DEFAULT_DEMOTION_TARGET_NODES +#endif + +struct demotion_nodes { + unsigned short nr; + short nodes[DEMOTION_TARGET_NODES]; +}; + +static struct demotion_nodes *node_demotion __read_mostly; + +/** + * next_demotion_node() - Get the next node in the demotion path + * @node: The starting node to lookup the next node + * + * Return: 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) +{ + struct demotion_nodes *nd; + unsigned short target_nr, index; + int target; + + if (!node_demotion) + return NUMA_NO_NODE; + + nd = &node_demotion[node]; + + /* + * 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_nr = READ_ONCE(nd->nr); + + switch (target_nr) { + case 0: + target = NUMA_NO_NODE; + goto out; + case 1: + index = 0; + break; + default: + /* + * If there are multiple target nodes, just select one + * target node randomly. + * + * In addition, we can also use round-robin to select + * target node, but we should introduce another variable + * for node_demotion[] to record last selected target node, + * that may cause cache ping-pong due to the changing of + * last target node. Or introducing per-cpu data to avoid + * caching issue, which seems more complicated. So selecting + * target node randomly seems better until now. + */ + index = get_random_int() % target_nr; + break; + } + + target = READ_ONCE(nd->nodes[index]); + +out: + rcu_read_unlock(); + return target; +} + #if defined(CONFIG_HOTPLUG_CPU) /* Disable reclaim-based migration. */ static void __disable_all_migrate_targets(void) _
