Re: [PATCH v5 4/9] mm/demotion: Build demotion targets based on explicit memory tiers

Ying Huang
2022-06-08T08:43:11Z

On Fri, 2022-06-03 at 19:12 +0530, Aneesh Kumar K.V wrote:
> This patch switch the demotion target building logic to use memory tiers
> instead of NUMA distance. All N_MEMORY NUMA nodes will be placed in the
> default tier 1 and additional memory tiers will be added by drivers like
> dax kmem.
>
> This patch builds the demotion target for a NUMA node by looking at all
> memory tiers below the tier to which the NUMA node belongs. The closest node
> in the immediately following memory tier is used as a demotion target.
>
> Since we are now only building demotion target for N_MEMORY NUMA nodes
> the CPU hotplug calls are removed in this patch.
>
> The rank approach allows us to keep memory tier device IDs stable even if there
> is a need to change the tier ordering among different memory tiers. e.g. DRAM
> nodes with CPUs will always be on memtier1, no matter how many tiers are higher
> or lower than these nodes. A new memory tier can be inserted into the tier
> hierarchy for a new set of nodes without affecting the node assignment of any
> existing memtier, provided that there is enough gap in the rank values for the
> new memtier.
>
> The absolute value of "rank" of a memtier doesn't necessarily carry any meaning.
> Its value relative to other memtiers decides the level of this memtier in the tier
> hierarchy.
>
> For now, This patch supports hardcoded rank values which are 300, 200, & 100 for
> memory tiers 0,1 & 2 respectively.
>
> Below is the sysfs interface to read the rank values of memory tier,
> /sys/devices/system/memtier/memtierN/rank
>
> This interface is read only for now. Write support can be added when there is
> a need of flexibility of more number of memory tiers(> 3) with flexibile ordering
> requirement among them.
>
> Suggested-by: Wei Xu <weixugc@google.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  include/linux/memory-tiers.h | 5 +
>  include/linux/migrate.h | 13 --
>  mm/memory-tiers.c | 269 ++++++++++++++++++++++++
>  mm/migrate.c | 394 -----------------------------------
>  mm/vmstat.c | 4 -
>  5 files changed, 274 insertions(+), 411 deletions(-)
>
> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
> index 33ef36395a20..adc2cb3bf5f8 100644
> --- a/include/linux/memory-tiers.h
> +++ b/include/linux/memory-tiers.h
> @@ -16,11 +16,16 @@
>  #define MAX_MEMORY_TIERS 3
>
>
>
>
>  extern bool numa_demotion_enabled;
> +int next_demotion_node(int node);
>  int node_get_memory_tier_id(int node);
>  int node_set_memory_tier(int node, int tier);
>  int node_reset_memory_tier(int node, int tier);
>  #else
>  #define numa_demotion_enabled false
> +static inline int next_demotion_node(int node)
> +{
> + return NUMA_NO_NODE;
> +}
>
>
>
>
>  #endif /* CONFIG_TIERED_MEMORY */
>
>
>
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 43e737215f33..93fab62e6548 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -75,19 +75,6 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
>
>
>
>
>  #endif /* CONFIG_MIGRATION */
>
>
>
>
> -#if defined(CONFIG_MIGRATION) && defined(CONFIG_NUMA)
> -extern void set_migration_target_nodes(void);
> -extern void migrate_on_reclaim_init(void);
> -extern int next_demotion_node(int node);
> -#else
> -static inline void set_migration_target_nodes(void) {}
> -static inline void migrate_on_reclaim_init(void) {}
> -static inline int next_demotion_node(int node)
> -{
> - return NUMA_NO_NODE;
> -}
> -#endif
> -
>  #ifdef CONFIG_COMPACTION
>  extern int PageMovable(struct page *page);
>  extern void __SetPageMovable(struct page *page, struct address_space *mapping);
> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> index 3f382d1f844a..0d05c0bfb79b 100644
> --- a/mm/memory-tiers.c
> +++ b/mm/memory-tiers.c
> @@ -4,6 +4,10 @@
>  #include <linux/nodemask.h>
>  #include <linux/slab.h>
>  #include <linux/memory-tiers.h>
> +#include <linux/random.h>
> +#include <linux/memory.h>
> +
> +#include "internal.h"
>
>
>
>
>  struct memory_tier {
>   struct list_head list;
> @@ -12,6 +16,10 @@ struct memory_tier {
>   int rank;
>  };
>
>
>
>
> +struct demotion_nodes {
> + nodemask_t preferred;
> +};
> +
>  #define to_memory_tier(device) container_of(device, struct memory_tier, dev)
>
>
>
>
>  static struct bus_type memory_tier_subsys = {
> @@ -19,9 +27,71 @@ static struct bus_type memory_tier_subsys = {
>   .dev_name = "memtier",
>  };
>
>
>
>
> +static void establish_migration_targets(void);
>  static DEFINE_MUTEX(memory_tier_lock);
>  static LIST_HEAD(memory_tiers);
>
>
>
>
> +/*
> + * node_demotion[] examples:
> + *
> + * Example 1:
> + *
> + * Node 0 & 1 are CPU + DRAM nodes, node 2 & 3 are PMEM nodes.
> + *
> + * node distances:
> + * node 0 1 2 3
> + * 0 10 20 30 40
> + * 1 20 10 40 30
> + * 2 30 40 10 40
> + * 3 40 30 40 10
> + *
> + * memory_tiers[0] = <empty>
> + * memory_tiers[1] = 0-1
> + * memory_tiers[2] = 2-3
> + *
> + * node_demotion[0].preferred = 2
> + * node_demotion[1].preferred = 3
> + * node_demotion[2].preferred = <empty>
> + * node_demotion[3].preferred = <empty>
> + *
> + * Example 2:
> + *
> + * Node 0 & 1 are CPU + DRAM nodes, node 2 is memory-only DRAM node.
> + *
> + * node distances:
> + * node 0 1 2
> + * 0 10 20 30
> + * 1 20 10 30
> + * 2 30 30 10
> + *
> + * memory_tiers[0] = <empty>
> + * memory_tiers[1] = 0-2
> + * memory_tiers[2] = <empty>
> + *
> + * node_demotion[0].preferred = <empty>
> + * node_demotion[1].preferred = <empty>
> + * node_demotion[2].preferred = <empty>
> + *
> + * Example 3:
> + *
> + * Node 0 is CPU + DRAM nodes, Node 1 is HBM node, node 2 is PMEM node.
> + *
> + * node distances:
> + * node 0 1 2
> + * 0 10 20 30
> + * 1 20 10 40
> + * 2 30 40 10
> + *
> + * memory_tiers[0] = 1
> + * memory_tiers[1] = 0
> + * memory_tiers[2] = 2
> + *
> + * node_demotion[0].preferred = 2
> + * node_demotion[1].preferred = 0
> + * node_demotion[2].preferred = <empty>
> + *
> + */
> +static struct demotion_nodes *node_demotion __read_mostly;
>
>
>
>
>  static ssize_t nodelist_show(struct device *dev,
>   struct device_attribute *attr, char *buf)
> @@ -202,6 +272,7 @@ static void node_remove_from_memory_tier(int node)
>   if (nodes_empty(memtier->nodelist))
>   unregister_memory_tier(memtier);
>
>
>
>
> + establish_migration_targets();
>  out:
>   mutex_unlock(&memory_tier_lock);
>  }
> @@ -263,6 +334,8 @@ int node_reset_memory_tier(int node, int tier)
>
>
>
>
>   if (nodes_empty(current_tier->nodelist))
>   unregister_memory_tier(current_tier);
> +
> + establish_migration_targets();
>  out:
>   mutex_unlock(&memory_tier_lock);
>
>
>
>
> @@ -276,13 +349,208 @@ int node_set_memory_tier(int node, int tier)
>
>
>
>
>   mutex_lock(&memory_tier_lock);
>   memtier = __node_get_memory_tier(node);
> + /*
> + * if node is already part of the tier proceed with the
> + * current tier value, because we might want to establish
> + * new migration paths now. The node might be added to a tier
> + * before it was made part of N_MEMORY, hence estabilish_migration_targets
> + * will have skipped this node.
> + */
>   if (!memtier)
>   ret = __node_set_memory_tier(node, tier);
> + establish_migration_targets();
> +
>   mutex_unlock(&memory_tier_lock);
>
>
>
>
>   return ret;
>  }
>
>
>
>
> +/**
> + * 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;
> + int target, nnodes, i;
> +
> + if (!node_demotion)
> + return NUMA_NO_NODE;
> +
> + nd = &node_demotion[node];
> +
> + /*
> + * node_demotion[] is updated without excluding this
> + * function from running.
> + *
> + * Make sure to use RCU over entire code blocks if
> + * node_demotion[] reads need to be consistent.
> + */
> + rcu_read_lock();
> +
> + nnodes = nodes_weight(nd->preferred);
> + if (!nnodes)
> + return NUMA_NO_NODE;

You forget to call rcu_read_unlock() before returning.

Best Regards,
Huang, Ying

> +
> + /*
> + * 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.
> + */
> + nnodes = get_random_int() % nnodes;
> + target = first_node(nd->preferred);
> + for (i = 0; i < nnodes; i++)
> + target = next_node(target, nd->preferred);
> +
> + rcu_read_unlock();
> +
> + return target;
> +}
> +
> +/* Disable reclaim-based migration. */
> +static void __disable_all_migrate_targets(void)
> +{
> + int node;
> +
> + for_each_node_mask(node, node_states[N_MEMORY])
> + node_demotion[node].preferred = NODE_MASK_NONE;
> +}
> +
> +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.
> + */
> + synchronize_rcu();
> +}
> +
> +/*
> + * Find an automatic demotion target for all memory
> + * nodes. Failing here is OK. It might just indicate
> + * being at the end of a chain.
> + */
> +static void establish_migration_targets(void)
> +{
> + struct memory_tier *memtier;
> + struct demotion_nodes *nd;
> + int target = NUMA_NO_NODE, node;
> + int distance, best_distance;
> + nodemask_t used;
> +
> + if (!node_demotion)
> + return;
> +
> + disable_all_migrate_targets();
> +
> + for_each_node_mask(node, node_states[N_MEMORY]) {
> + best_distance = -1;
> + nd = &node_demotion[node];
> +
> + memtier = __node_get_memory_tier(node);
> + if (!memtier || list_is_last(&memtier->list, &memory_tiers))
> + continue;
> + /*
> + * Get the next memtier to find the demotion node list.
> + */
> + memtier = list_next_entry(memtier, list);
> +
> + /*
> + * find_next_best_node, use 'used' nodemask as a skip list.
> + * Add all memory nodes except the selected memory tier
> + * nodelist to skip list so that we find the best node from the
> + * memtier nodelist.
> + */
> + nodes_andnot(used, node_states[N_MEMORY], memtier->nodelist);
> +
> + /*
> + * Find all the nodes in the memory tier node list of same best distance.
> + * add them to the preferred mask. We randomly select between nodes
> + * in the preferred mask when allocating pages during demotion.
> + */
> + do {
> + target = find_next_best_node(node, &used);
> + if (target == NUMA_NO_NODE)
> + break;
> +
> + distance = node_distance(node, target);
> + if (distance == best_distance || best_distance == -1) {
> + best_distance = distance;
> + node_set(target, nd->preferred);
> + } else {
> + break;
> + }
> + } while (1);
> + }
> +}
> +
> +/*
> + * This runs whether reclaim-based migration is enabled or not,
> + * which ensures that the user can turn reclaim-based migration
> + * at any time without needing to recalculate migration targets.
> + */
> +static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
> + unsigned long action, void *_arg)
> +{
> + struct memory_notify *arg = _arg;
> +
> + /*
> + * Only update the node migration order when a node is
> + * changing status, like online->offline.
> + */
> + if (arg->status_change_nid < 0)
> + return notifier_from_errno(0);
> +
> + switch (action) {
> + case MEM_OFFLINE:
> + /*
> + * In case we are moving out of N_MEMORY. Keep the node
> + * in the memory tier so that when we bring memory online,
> + * they appear in the right memory tier. We still need
> + * to rebuild the demotion order.
> + */
> + mutex_lock(&memory_tier_lock);
> + establish_migration_targets();
> + mutex_unlock(&memory_tier_lock);
> + break;
> + case MEM_ONLINE:
> + /*
> + * We ignore the error here, if the node already have the tier
> + * registered, we will continue to use that for the new memory
> + * we are adding here.
> + */
> + node_set_memory_tier(arg->status_change_nid, DEFAULT_MEMORY_TIER);
> + break;
> + }
> +
> + return notifier_from_errno(0);
> +}
> +
> +static void __init migrate_on_reclaim_init(void)
> +{
> + node_demotion = kcalloc(MAX_NUMNODES, sizeof(struct demotion_nodes),
> + GFP_KERNEL);
> + WARN_ON(!node_demotion);
> +
> + hotplug_memory_notifier(migrate_on_reclaim_callback, 100);
> +}
> +
>  static int __init memory_tier_init(void)
>  {
>   int ret;
> @@ -302,6 +570,7 @@ static int __init memory_tier_init(void)
>
>
>
>
>   /* CPU only nodes are not part of memory tiers. */
>   memtier->nodelist = node_states[N_MEMORY];
> + migrate_on_reclaim_init();
>
>
>
>
>   return 0;
>  }
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 29cacc217e38..0b554625a219 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2116,398 +2116,4 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
>   return 0;
>  }
>  #endif /* CONFIG_NUMA_BALANCING */
> -
> -/*
> - * 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;
> -}
> -
> -/* Disable reclaim-based migration. */
> -static void __disable_all_migrate_targets(void)
> -{
> - int node, i;
> -
> - if (!node_demotion)
> - return;
> -
> - 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)
> -{
> - __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 best_distance)
> -{
> - int migration_target, index, val;
> - struct demotion_nodes *nd;
> -
> - if (!node_demotion)
> - return NUMA_NO_NODE;
> -
> - nd = &node_demotion[node];
> -
> - migration_target = find_next_best_node(node, used);
> - if (migration_target == NUMA_NO_NODE)
> - return NUMA_NO_NODE;
> -
> - /*
> - * 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 (best_distance != -1) {
> - val = node_distance(node, migration_target);
> - if (val > best_distance)
> - goto out_clear;
> - }
> -
> - index = nd->nr;
> - if (WARN_ONCE(index >= DEMOTION_TARGET_NODES,
> - "Exceeds maximum demotion target nodes\n"))
> - goto out_clear;
> -
> - nd->nodes[index] = migration_target;
> - nd->nr++;
> -
> - return migration_target;
> -out_clear:
> - node_clear(migration_target, *used);
> - return NUMA_NO_NODE;
> -}
> -
> -/*
> - * 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. 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
> - * with itself. Exclusion is provided by memory hotplug events
> - * being single-threaded.
> - */
> -static void __set_migration_target_nodes(void)
> -{
> - nodemask_t next_pass;
> - nodemask_t this_pass;
> - nodemask_t used_targets = NODE_MASK_NONE;
> - int node, best_distance;
> -
> - /*
> - * 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) {
> - best_distance = -1;
> -
> - /*
> - * 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.
> - */
> - 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
> - * 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.
> - */
> -void set_migration_target_nodes(void)
> -{
> - get_online_mems();
> - __set_migration_target_nodes();
> - put_online_mems();
> -}
> -
> -/*
> - * This leaves migrate-on-reclaim transiently disabled between
> - * the MEM_GOING_OFFLINE and MEM_OFFLINE events. This runs
> - * whether reclaim-based migration is enabled or not, which
> - * ensures that the user can turn reclaim-based migration at
> - * any time without needing to recalculate migration targets.
> - *
> - * These callbacks already hold get_online_mems(). That is why
> - * __set_migration_target_nodes() can be used as opposed to
> - * set_migration_target_nodes().
> - */
> -#ifdef CONFIG_MEMORY_HOTPLUG
> -static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
> - unsigned long action, void *_arg)
> -{
> - struct memory_notify *arg = _arg;
> -
> - /*
> - * Only update the node migration order when a node is
> - * changing status, like online->offline. This avoids
> - * the overhead of synchronize_rcu() in most cases.
> - */
> - if (arg->status_change_nid < 0)
> - return notifier_from_errno(0);
> -
> - switch (action) {
> - case MEM_GOING_OFFLINE:
> - /*
> - * Make sure there are not transient states where
> - * an offline node is a migration target. This
> - * will leave migration disabled until the offline
> - * completes and the MEM_OFFLINE case below runs.
> - */
> - disable_all_migrate_targets();
> - break;
> - case MEM_OFFLINE:
> - case MEM_ONLINE:
> - /*
> - * Recalculate the target nodes once the node
> - * reaches its final state (online or offline).
> - */
> - __set_migration_target_nodes();
> - break;
> - case MEM_CANCEL_OFFLINE:
> - /*
> - * MEM_GOING_OFFLINE disabled all the migration
> - * targets. Reenable them.
> - */
> - __set_migration_target_nodes();
> - break;
> - case MEM_GOING_ONLINE:
> - case MEM_CANCEL_ONLINE:
> - break;
> - }
> -
> - return notifier_from_errno(0);
> -}
> -#endif
> -
> -void __init migrate_on_reclaim_init(void)
> -{
> - node_demotion = kcalloc(nr_node_ids,
> - sizeof(struct demotion_nodes),
> - GFP_KERNEL);
> - WARN_ON(!node_demotion);
> -#ifdef CONFIG_MEMORY_HOTPLUG
> - hotplug_memory_notifier(migrate_on_reclaim_callback, 100);
> -#endif
> - /*
> - * At this point, all numa nodes with memory/CPus have their state
> - * properly set, so we can build the demotion order now.
> - * Let us hold the cpu_hotplug lock just, as we could possibily have
> - * CPU hotplug events during boot.
> - */
> - cpus_read_lock();
> - set_migration_target_nodes();
> - cpus_read_unlock();
> -}
>  #endif /* CONFIG_NUMA */
> -
> -
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index da525bfb6f4a..835e3c028f35 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -28,7 +28,6 @@
>  #include <linux/mm_inline.h>
>  #include <linux/page_ext.h>
>  #include <linux/page_owner.h>
> -#include <linux/migrate.h>
>
>
>
>
>  #include "internal.h"
>
>
>
>
> @@ -2060,7 +2059,6 @@ static int vmstat_cpu_online(unsigned int cpu)
>
>
>
>
>   if (!node_state(cpu_to_node(cpu), N_CPU)) {
>   node_set_state(cpu_to_node(cpu), N_CPU);
> - set_migration_target_nodes();
>   }
>
>
>
>
>   return 0;
> @@ -2085,7 +2083,6 @@ static int vmstat_cpu_dead(unsigned int cpu)
>   return 0;
>
>
>
>
>   node_clear_state(node, N_CPU);
> - set_migration_target_nodes();
>
>
>
>
>   return 0;
>  }
> @@ -2118,7 +2115,6 @@ void __init init_mm_internals(void)
>
>
>
>
>   start_shepherd_timer();
>  #endif
> - migrate_on_reclaim_init();
>  #ifdef CONFIG_PROC_FS
>   proc_create_seq("buddyinfo", 0444, NULL, &fragmentation_op);
>   proc_create_seq("pagetypeinfo", 0400, NULL, &pagetypeinfo_op);