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To prepare for a premature release of percpu per-node data, let's pretend that lruvec_stat_cpu is a rcu-protected pointer, which can be NULL. This patch adds corresponding checks whenever required. Signed-off-by: Roman Gushchin --- include/linux/memcontrol.h | 21 +++++++++++++++------ mm/memcontrol.c | 11 +++++++++-- 2 files changed, 24 insertions(+), 8 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 05ca77767c6a..8ac04632002a 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -126,7 +126,7 @@ struct memcg_shrinker_map { struct mem_cgroup_per_node { struct lruvec lruvec; - struct lruvec_stat __percpu *lruvec_stat_cpu; + struct lruvec_stat __rcu /* __percpu */ *lruvec_stat_cpu; atomic_long_t lruvec_stat[NR_VM_NODE_STAT_ITEMS]; unsigned long lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS]; @@ -682,6 +682,7 @@ static inline unsigned long lruvec_page_state(struct lruvec *lruvec, static inline void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, int val) { + struct lruvec_stat __percpu *lruvec_stat_cpu; struct mem_cgroup_per_node *pn; long x; @@ -697,12 +698,20 @@ static inline void __mod_lruvec_state(struct lruvec *lruvec, __mod_memcg_state(pn->memcg, idx, val); /* Update lruvec */ - x = val + __this_cpu_read(pn->lruvec_stat_cpu->count[idx]); - if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) { - atomic_long_add(x, &pn->lruvec_stat[idx]); - x = 0; + rcu_read_lock(); + lruvec_stat_cpu = (struct lruvec_stat __percpu *) + rcu_dereference(pn->lruvec_stat_cpu); + if (likely(lruvec_stat_cpu)) { + x = val + __this_cpu_read(lruvec_stat_cpu->count[idx]); + if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) { + atomic_long_add(x, &pn->lruvec_stat[idx]); + x = 0; + } + __this_cpu_write(lruvec_stat_cpu->count[idx], x); + } else { + atomic_long_add(val, &pn->lruvec_stat[idx]); } - __this_cpu_write(pn->lruvec_stat_cpu->count[idx], x); + rcu_read_unlock(); } static inline void mod_lruvec_state(struct lruvec *lruvec, diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 803c772f354b..8f3cac02221a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2122,6 +2122,7 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) static int memcg_hotplug_cpu_dead(unsigned int cpu) { struct memcg_vmstats_percpu __percpu *vmstats_percpu; + struct lruvec_stat __percpu *lruvec_stat_cpu; struct memcg_stock_pcp *stock; struct mem_cgroup *memcg; @@ -2152,7 +2153,12 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu) struct mem_cgroup_per_node *pn; pn = mem_cgroup_nodeinfo(memcg, nid); - x = this_cpu_xchg(pn->lruvec_stat_cpu->count[i], 0); + + lruvec_stat_cpu = (struct lruvec_stat __percpu*) + rcu_dereference(pn->lruvec_stat_cpu); + if (!lruvec_stat_cpu) + continue; + x = this_cpu_xchg(lruvec_stat_cpu->count[i], 0); if (x) atomic_long_add(x, &pn->lruvec_stat[i]); } @@ -4430,7 +4436,8 @@ static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node) if (!pn) return 1; - pn->lruvec_stat_cpu = alloc_percpu(struct lruvec_stat); + rcu_assign_pointer(pn->lruvec_stat_cpu, + alloc_percpu(struct lruvec_stat)); if (!pn->lruvec_stat_cpu) { kfree(pn); return 1; -- 2.20.1