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    SubjectRe: [PATCH v2 09/11] memcg: propagate kmem limiting information to children
    (2012/08/09 22:01), Glauber Costa wrote:
    > The current memcg slab cache management fails to present satisfatory
    > hierarchical behavior in the following scenario:
    >
    > -> /cgroups/memory/A/B/C
    >
    > * kmem limit set at A,
    > * A and B have no tasks,
    > * span a new task in in C.
    >
    > Because kmem_accounted is a boolean that was not set for C, no
    > accounting would be done. This is, however, not what we expect.
    >
    > The basic idea, is that when a cgroup is limited, we walk the tree
    > upwards (something Kame and I already thought about doing for other
    > purposes), and make sure that we store the information about the parent
    > being limited in kmem_accounted (that is turned into a bitmap: two
    > booleans would not be space efficient). The code for that is taken from
    > sched/core.c. My reasons for not putting it into a common place is to
    > dodge the type issues that would arise from a common implementation
    > between memcg and the scheduler - but I think that it should ultimately
    > happen, so if you want me to do it now, let me know.
    >
    > We do the reverse operation when a formerly limited cgroup becomes
    > unlimited.
    >
    > Signed-off-by: Glauber Costa <glommer@parallels.com>
    > CC: Christoph Lameter <cl@linux.com>
    > CC: Pekka Enberg <penberg@cs.helsinki.fi>
    > CC: Michal Hocko <mhocko@suse.cz>
    > CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > CC: Johannes Weiner <hannes@cmpxchg.org>
    > CC: Suleiman Souhlal <suleiman@google.com>



    > ---
    > mm/memcontrol.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++++------
    > 1 file changed, 79 insertions(+), 9 deletions(-)
    >
    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index 3216292..3d30b79 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -295,7 +295,8 @@ struct mem_cgroup {
    > * Should the accounting and control be hierarchical, per subtree?
    > */
    > bool use_hierarchy;
    > - bool kmem_accounted;
    > +
    > + unsigned long kmem_accounted; /* See KMEM_ACCOUNTED_*, below */
    >
    > bool oom_lock;
    > atomic_t under_oom;
    > @@ -348,6 +349,38 @@ struct mem_cgroup {
    > #endif
    > };
    >
    > +enum {
    > + KMEM_ACCOUNTED_THIS, /* accounted by this cgroup itself */
    > + KMEM_ACCOUNTED_PARENT, /* accounted by any of its parents. */
    > +};
    > +
    > +#ifdef CONFIG_MEMCG_KMEM
    > +static bool memcg_kmem_account(struct mem_cgroup *memcg)
    > +{
    > + return !test_and_set_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted);
    > +}
    > +
    > +static bool memcg_kmem_clear_account(struct mem_cgroup *memcg)
    > +{
    > + return test_and_clear_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted);
    > +}
    > +
    > +static bool memcg_kmem_is_accounted(struct mem_cgroup *memcg)
    > +{
    > + return test_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted);
    > +}
    > +
    > +static void memcg_kmem_account_parent(struct mem_cgroup *memcg)
    > +{
    > + set_bit(KMEM_ACCOUNTED_PARENT, &memcg->kmem_accounted);
    > +}
    > +
    > +static void memcg_kmem_clear_account_parent(struct mem_cgroup *memcg)
    > +{
    > + clear_bit(KMEM_ACCOUNTED_PARENT, &memcg->kmem_accounted);
    > +}
    > +#endif /* CONFIG_MEMCG_KMEM */
    > +
    > /* Stuffs for move charges at task migration. */
    > /*
    > * Types of charges to be moved. "move_charge_at_immitgrate" is treated as a
    > @@ -614,7 +647,7 @@ EXPORT_SYMBOL(__memcg_kmem_free_page);
    >
    > static void disarm_kmem_keys(struct mem_cgroup *memcg)
    > {
    > - if (memcg->kmem_accounted)
    > + if (test_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted))
    > static_key_slow_dec(&memcg_kmem_enabled_key);
    > }
    > #else
    > @@ -4171,17 +4204,54 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
    > static void memcg_update_kmem_limit(struct mem_cgroup *memcg, u64 val)
    > {
    > #ifdef CONFIG_MEMCG_KMEM
    > - /*
    > - * Once enabled, can't be disabled. We could in theory disable it if we
    > - * haven't yet created any caches, or if we can shrink them all to
    > - * death. But it is not worth the trouble.
    > - */
    > + struct mem_cgroup *iter;
    > +
    > mutex_lock(&set_limit_mutex);
    > - if (!memcg->kmem_accounted && val != RESOURCE_MAX) {
    > + if ((val != RESOURCE_MAX) && memcg_kmem_account(memcg)) {
    > +
    > + /*
    > + * Once enabled, can't be disabled. We could in theory disable
    > + * it if we haven't yet created any caches, or if we can shrink
    > + * them all to death. But it is not worth the trouble
    > + */
    > static_key_slow_inc(&memcg_kmem_enabled_key);
    > - memcg->kmem_accounted = true;
    > +
    > + if (!memcg->use_hierarchy)
    > + goto out;
    > +
    > + for_each_mem_cgroup_tree(iter, memcg) {
    > + if (iter == memcg)
    > + continue;
    > + memcg_kmem_account_parent(iter);
    > + }

    Could you add an explanation comment ?


    > + } else if ((val == RESOURCE_MAX) && memcg_kmem_clear_account(memcg)) {
    > +
    > + if (!memcg->use_hierarchy)
    > + goto out;
    > +
    ditto.

    > + for_each_mem_cgroup_tree(iter, memcg) {
    > + struct mem_cgroup *parent;
    > +
    > + if (iter == memcg)
    > + continue;
    > + /*
    > + * We should only have our parent bit cleared if none
    > + * of our parents are accounted. The transversal order
    > + * of our iter function forces us to always look at the
    > + * parents.
    > + */
    > + parent = parent_mem_cgroup(iter);
    > + for (; parent != memcg; parent = parent_mem_cgroup(iter))
    > + if (memcg_kmem_is_accounted(parent))
    > + goto noclear;
    > + memcg_kmem_clear_account_parent(iter);


    Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>



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