On Mon 18-06-12 14:27:58, Glauber Costa wrote:
> Right now we free struct memcg with kfree right after a
> rcu grace period, but defer it if we need to use vfree() to get
> rid of that memory area. We do that by need, because we need vfree
> to be called in a process context.
>
> This patch unifies this behavior, by ensuring that even kfree will
> happen in a separate thread. The goal is to have a stable place to
> call the upcoming jump label destruction function outside the realm
> of the complicated and quite far-reaching cgroup lock (that can't be
> held when calling neither the cpu_hotplug.lock nor the jump_label_mutex)
This one is in memcg-devel (mmotm) tree for quite some time with acks
from me and Kamezawa.
> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
> CC: Tejun Heo <tj@xxxxxxxxxx>
> CC: Li Zefan <lizefan@xxxxxxxxxx>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> CC: Johannes Weiner <hannes@xxxxxxxxxxx>
> CC: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/memcontrol.c | 24 +++++++++++++-----------
> 1 file changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e3b528e..ce15be4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -245,8 +245,8 @@ struct mem_cgroup {
> */
> struct rcu_head rcu_freeing;
> /*
> - * But when using vfree(), that cannot be done at
> - * interrupt time, so we must then queue the work.
> + * We also need some space for a worker in deferred freeing.
> + * By the time we call it, rcu_freeing is not longer in use.
> */
> struct work_struct work_freeing;
> };
> @@ -4826,23 +4826,28 @@ out_free:
> }
>
> /*
> - * Helpers for freeing a vzalloc()ed mem_cgroup by RCU,
> + * Helpers for freeing a kmalloc()ed/vzalloc()ed mem_cgroup by RCU,
> * but in process context. The work_freeing structure is overlaid
> * on the rcu_freeing structure, which itself is overlaid on memsw.
> */
> -static void vfree_work(struct work_struct *work)
> +static void free_work(struct work_struct *work)
> {
> struct mem_cgroup *memcg;
> + int size = sizeof(struct mem_cgroup);
>
> memcg = container_of(work, struct mem_cgroup, work_freeing);
> - vfree(memcg);
> + if (size < PAGE_SIZE)
> + kfree(memcg);
> + else
> + vfree(memcg);
> }
> -static void vfree_rcu(struct rcu_head *rcu_head)
> +
> +static void free_rcu(struct rcu_head *rcu_head)
> {
> struct mem_cgroup *memcg;
>
> memcg = container_of(rcu_head, struct mem_cgroup, rcu_freeing);
> - INIT_WORK(&memcg->work_freeing, vfree_work);
> + INIT_WORK(&memcg->work_freeing, free_work);
> schedule_work(&memcg->work_freeing);
> }
>
> @@ -4868,10 +4873,7 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
> free_mem_cgroup_per_zone_info(memcg, node);
>
> free_percpu(memcg->stat);
> - if (sizeof(struct mem_cgroup) < PAGE_SIZE)
> - kfree_rcu(memcg, rcu_freeing);
> - else
> - call_rcu(&memcg->rcu_freeing, vfree_rcu);
> + call_rcu(&memcg->rcu_freeing, free_rcu);
> }
>
> static void mem_cgroup_get(struct mem_cgroup *memcg)
> --
> 1.7.10.2
>
> --
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--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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