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    Subject[PATCH v12 6/8] mm/demotion: Add pg_data_t member to track node memory tier details
    Date
    Also update different helpes to use NODE_DATA()->memtier. Since
    node specific memtier can change based on the reassignment of
    NUMA node to a different memory tiers, accessing NODE_DATA()->memtier
    needs to happen under an rcu read lock or memory_tier_lock.

    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
    ---
    include/linux/mmzone.h | 3 +++
    mm/memory-tiers.c | 39 +++++++++++++++++++++++++++++++++------
    2 files changed, 36 insertions(+), 6 deletions(-)

    diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
    index aab70355d64f..353812495a70 100644
    --- a/include/linux/mmzone.h
    +++ b/include/linux/mmzone.h
    @@ -928,6 +928,9 @@ typedef struct pglist_data {
    /* Per-node vmstats */
    struct per_cpu_nodestat __percpu *per_cpu_nodestats;
    atomic_long_t vm_stat[NR_VM_NODE_STAT_ITEMS];
    +#ifdef CONFIG_NUMA
    + struct memory_tier __rcu *memtier;
    +#endif
    } pg_data_t;

    #define node_present_pages(nid) (NODE_DATA(nid)->node_present_pages)
    diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
    index 97634337803c..44f6676bc2c8 100644
    --- a/mm/memory-tiers.c
    +++ b/mm/memory-tiers.c
    @@ -5,6 +5,7 @@
    #include <linux/kobject.h>
    #include <linux/memory.h>
    #include <linux/random.h>
    +#include <linux/mmzone.h>
    #include <linux/memory-tiers.h>

    #include "internal.h"
    @@ -144,12 +145,18 @@ static struct memory_tier *find_create_memory_tier(struct memory_dev_type *memty

    static struct memory_tier *__node_get_memory_tier(int node)
    {
    - struct memory_dev_type *memtype;
    + pg_data_t *pgdat;

    - memtype = node_memory_types[node];
    - if (memtype)
    - return memtype->memtier;
    - return NULL;
    + pgdat = NODE_DATA(node);
    + if (!pgdat)
    + return NULL;
    + /*
    + * Since we hold memory_tier_lock, we can avoid
    + * RCU read locks when accessing the details. No
    + * parallel updates are possible here.
    + */
    + return rcu_dereference_check(pgdat->memtier,
    + lockdep_is_held(&memory_tier_lock));
    }

    #ifdef CONFIG_MIGRATION
    @@ -292,6 +299,7 @@ static inline void establish_demotion_targets(void) {}

    static void init_node_memory_tier(int node)
    {
    + pg_data_t *pgdat = NODE_DATA(node);
    struct memory_tier *memtier;

    mutex_lock(&memory_tier_lock);
    @@ -313,8 +321,12 @@ static void init_node_memory_tier(int node)
    }
    memtype = node_memory_types[node];
    memtier = find_create_memory_tier(memtype);
    + if (IS_ERR(memtier))
    + goto err_out;
    + rcu_assign_pointer(pgdat->memtier, memtier);
    }
    establish_demotion_targets();
    +err_out:
    mutex_unlock(&memory_tier_lock);
    }

    @@ -326,13 +338,26 @@ static void destroy_memory_tier(struct memory_tier *memtier)

    static void clear_node_memory_tier(int node)
    {
    + pg_data_t *pgdat;
    struct memory_tier *current_memtier;

    + pgdat = NODE_DATA(node);
    + if (!pgdat)
    + return;
    +
    mutex_lock(&memory_tier_lock);
    + /*
    + * Make sure that anybody looking at NODE_DATA who finds
    + * a valid memtier finds memory_dev_types with nodes still
    + * linked to the memtier. We achieve this by waiting for
    + * rcu read section to finish using synchronize_rcu.
    + */
    current_memtier = __node_get_memory_tier(node);
    if (current_memtier) {
    struct memory_dev_type *memtype;

    + rcu_assign_pointer(pgdat->memtier, NULL);
    + synchronize_rcu();
    memtype = node_memory_types[node];
    node_clear(node, memtype->nodes);
    if (nodes_empty(memtype->nodes)) {
    @@ -400,8 +425,10 @@ static int __init memory_tier_init(void)
    panic("%s() failed to register memory tier: %ld\n",
    __func__, PTR_ERR(memtier));

    - for_each_node_state(node, N_MEMORY)
    + for_each_node_state(node, N_MEMORY) {
    node_memory_types[node] = &default_dram_type;
    + rcu_assign_pointer(NODE_DATA(node)->memtier, memtier);
    + }

    mutex_unlock(&memory_tier_lock);
    #ifdef CONFIG_MIGRATION
    --
    2.37.1
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