Hi,
> +/* 0 is unused */
> +static atomic_t mem_cgroup_num;
> +#define NR_MEMCG_GROUPS (CONFIG_MEM_CGROUP_MAX_GROUPS + 1)
> +static struct mem_cgroup *mem_cgroups[NR_MEMCG_GROUPS] __read_mostly;
> +
> +/* Must be called under rcu_read_lock */
> +static struct mem_cgroup *id_to_memcg(unsigned short id)
> +{
> + struct mem_cgroup *ret;
> + /* see mem_cgroup_free() */
> + ret = rcu_dereference_check(mem_cgroups[id], rch_read_lock_held());
> + if (likely(ret && ret->valid))
> + return ret;
> + return NULL;
> +}
> +
I prefer "mem" to "ret".
> @@ -2231,7 +2244,7 @@ __mem_cgroup_commit_charge_swapin(struct
>
> id = swap_cgroup_record(ent, 0);
> rcu_read_lock();
> - memcg = mem_cgroup_lookup(id);
> + memcg = id_to_memcg(id);
> if (memcg) {
> /*
> * This recorded memcg can be obsolete one. So, avoid
> @@ -2240,9 +2253,10 @@ __mem_cgroup_commit_charge_swapin(struct
> if (!mem_cgroup_is_root(memcg))
> res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> mem_cgroup_swap_statistics(memcg, false);
> + rcu_read_unlock();
> mem_cgroup_put(memcg);
> - }
> - rcu_read_unlock();
> + } else
> + rcu_read_unlock();
> }
> /*
> * At swapin, we may charge account against cgroup which has no tasks.
> @@ -2495,7 +2509,7 @@ void mem_cgroup_uncharge_swap(swp_entry_
>
> id = swap_cgroup_record(ent, 0);
> rcu_read_lock();
> - memcg = mem_cgroup_lookup(id);
> + memcg = id_to_memcg(id);
> if (memcg) {
> /*
> * We uncharge this because swap is freed.
> @@ -2504,9 +2518,10 @@ void mem_cgroup_uncharge_swap(swp_entry_
> if (!mem_cgroup_is_root(memcg))
> res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> mem_cgroup_swap_statistics(memcg, false);
> + rcu_read_unlock();
> mem_cgroup_put(memcg);
> - }
> - rcu_read_unlock();
> + } else
> + rcu_read_unlock();
> }
>
> /**
Could you explain why we need rcu_read_unlock() before mem_cgroup_put() ?
I suspect that it's because mem_cgroup_put() can free the memcg, but do we
need mem->valid then ?
Thanks,
Daisuke Nishimura.
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