Re: [PATCH v4 4/6] memcg: replace cgroup_lock with memcg specific memcg_lock

Michal Hocko
2013-01-22T14:00:26Z

On Tue 22-01-13 17:47:39, Glauber Costa wrote:
> After the preparation work done in earlier patches, the cgroup_lock can
> be trivially replaced with a memcg-specific lock. This is an automatic
> translation in every site the values involved were queried.
>
> The sites were values are written, however, used to be naturally called
> under cgroup_lock. This is the case for instance of the css_online
> callback. For those, we now need to explicitly add the memcg lock.
>
> With this, all the calls to cgroup_lock outside cgroup core are gone.
>
> Signed-off-by: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>

Acked-by: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>

Thanks!
> ---
> mm/memcontrol.c | 37 ++++++++++++++++++++-----------------
> 1 file changed, 20 insertions(+), 17 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6d3ad21..f5decb7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -470,6 +470,13 @@ enum res_type {
> #define MEM_CGROUP_RECLAIM_SHRINK_BIT 0x1
> #define MEM_CGROUP_RECLAIM_SHRINK (1 << MEM_CGROUP_RECLAIM_SHRINK_BIT)
>
> +/*
> + * The memcg_create_mutex will be held whenever a new cgroup is created.
> + * As a consequence, any change that needs to protect against new child cgroups
> + * appearing has to hold it as well.
> + */
> +static DEFINE_MUTEX(memcg_create_mutex);
> +
> static void mem_cgroup_get(struct mem_cgroup *memcg);
> static void mem_cgroup_put(struct mem_cgroup *memcg);
>
> @@ -4730,8 +4737,8 @@ static inline bool __memcg_has_children(struct mem_cgroup *memcg)
> }
>
> /*
> - * must be called with cgroup_lock held, unless the cgroup is guaranteed to be
> - * already dead (like in mem_cgroup_force_empty, for instance). This is
> + * must be called with memcg_create_mutex held, unless the cgroup is guaranteed
> + * to be already dead (like in mem_cgroup_force_empty, for instance). This is
> * different than mem_cgroup_count_children, in the sense that we don't really
> * care how many children we have, we only need to know if we have any. It is
> * also count any memcg without hierarchy as infertile for that matter.
> @@ -4811,7 +4818,7 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
> if (parent)
> parent_memcg = mem_cgroup_from_cont(parent);
>
> - cgroup_lock();
> + mutex_lock(&memcg_create_mutex);
>
> if (memcg->use_hierarchy == val)
> goto out;
> @@ -4834,7 +4841,7 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
> retval = -EINVAL;
>
> out:
> - cgroup_unlock();
> + mutex_unlock(&memcg_create_mutex);
>
> return retval;
> }
> @@ -4933,14 +4940,8 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
> *
> * After it first became limited, changes in the value of the limit are
> * of course permitted.
> - *
> - * Taking the cgroup_lock is really offensive, but it is so far the only
> - * way to guarantee that no children will appear. There are plenty of
> - * other offenders, and they should all go away. Fine grained locking
> - * is probably the way to go here. When we are fully hierarchical, we
> - * can also get rid of the use_hierarchy check.
> */
> - cgroup_lock();
> + mutex_lock(&memcg_create_mutex);
> mutex_lock(&set_limit_mutex);
> if (!memcg->kmem_account_flags && val != RESOURCE_MAX) {
> if (cgroup_task_count(cont) || memcg_has_children(memcg)) {
> @@ -4967,7 +4968,7 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
> ret = res_counter_set_limit(&memcg->kmem, val);
> out:
> mutex_unlock(&set_limit_mutex);
> - cgroup_unlock();
> + mutex_unlock(&memcg_create_mutex);
>
> /*
> * We are by now familiar with the fact that we can't inc the static
> @@ -5356,17 +5357,17 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
>
> parent = mem_cgroup_from_cont(cgrp->parent);
>
> - cgroup_lock();
> + mutex_lock(&memcg_create_mutex);
>
> /* If under hierarchy, only empty-root can set this value */
> if ((parent->use_hierarchy) || memcg_has_children(memcg)) {
> - cgroup_unlock();
> + mutex_unlock(&memcg_create_mutex);
> return -EINVAL;
> }
>
> memcg->swappiness = val;
>
> - cgroup_unlock();
> + mutex_unlock(&memcg_create_mutex);
>
> return 0;
> }
> @@ -5692,7 +5693,7 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
>
> parent = mem_cgroup_from_cont(cgrp->parent);
>
> - cgroup_lock();
> + mutex_lock(&memcg_create_mutex);
> /* oom-kill-disable is a flag for subhierarchy. */
> if ((parent->use_hierarchy) ||
> (memcg->use_hierarchy && !list_empty(&cgrp->children))) {
> @@ -5702,7 +5703,7 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
> memcg->oom_kill_disable = val;
> if (!val)
> memcg_oom_recover(memcg);
> - cgroup_unlock();
> + mutex_unlock(&memcg_create_mutex);
> return 0;
> }
>
> @@ -6140,6 +6141,7 @@ mem_cgroup_css_online(struct cgroup *cont)
> if (!cont->parent)
> return 0;
>
> + mutex_lock(&memcg_create_mutex);
> memcg = mem_cgroup_from_cont(cont);
> parent = mem_cgroup_from_cont(cont->parent);
>
> @@ -6173,6 +6175,7 @@ mem_cgroup_css_online(struct cgroup *cont)
> }
>
> error = memcg_init_kmem(memcg, &mem_cgroup_subsys);
> + mutex_unlock(&memcg_create_mutex);
> if (error) {
> /*
> * We call put now because our (and parent's) refcnts
> --
> 1.8.1
>

--
Michal Hocko
SUSE Labs