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Subject[PATCH RESEND -mm 05/12] memcg: add pointer from memcg_cache_params to cache
Date
While iterating over the memcg_slab_caches list we need to obtain the
cache a particular memcg_params is corresponding to, because
memcg_params are actually linked, not caches. Currently to achieve that,
we employ the fact that each root cache tracks all its child caches in
its memcg_caches array, so that given a memcg_params we can find the
memcg cache by doing something like this:

root = memcg_params->root_cache;
memcg = memcg_params->memcg;
memcg_cache = root->memcg_params->memcg_caches[memcg->kmemcg_id];

Apart from being cumbersome, this is not going to work when reparenting
of memcg caches is introduced. So let's embed a pointer back to the
memcg cache into the memcg_cache_params struct.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
---
include/linux/slab.h | 2 ++
mm/memcontrol.c | 28 +++-------------------------
2 files changed, 5 insertions(+), 25 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index ee9f1b0382ac..f2fd4212976e 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -520,6 +520,7 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
*
* Child caches will hold extra metadata needed for its operation. Fields are:
*
+ * @cachep: back pointer to the memcg cache
* @memcg: pointer to the memcg this cache belongs to
* @list: list_head for the list of all caches in this memcg
* @root_cache: pointer to the global, root cache, this cache was derived from
@@ -536,6 +537,7 @@ struct memcg_cache_params {
struct kmem_cache *memcg_caches[0];
};
struct {
+ struct kmem_cache *cachep;
struct mem_cgroup *memcg;
struct list_head list;
struct kmem_cache *root_cache;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3659d90d5a40..626a37e01126 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2912,19 +2912,6 @@ static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
memcg_kmem_is_active(memcg);
}

-/*
- * This is a bit cumbersome, but it is rarely used and avoids a backpointer
- * in the memcg_cache_params struct.
- */
-static struct kmem_cache *memcg_params_to_cache(struct memcg_cache_params *p)
-{
- struct kmem_cache *cachep;
-
- VM_BUG_ON(p->is_root_cache);
- cachep = p->root_cache;
- return cache_from_memcg_idx(cachep, memcg_cache_id(p->memcg));
-}
-
#ifdef CONFIG_SLABINFO
static int mem_cgroup_slabinfo_read(struct seq_file *m, void *v)
{
@@ -2938,7 +2925,7 @@ static int mem_cgroup_slabinfo_read(struct seq_file *m, void *v)

mutex_lock(&memcg->slab_caches_mutex);
list_for_each_entry(params, &memcg->memcg_slab_caches, list)
- cache_show(memcg_params_to_cache(params), m);
+ cache_show(params->cachep, m);
mutex_unlock(&memcg->slab_caches_mutex);

return 0;
@@ -3137,6 +3124,7 @@ int memcg_alloc_cache_params(struct mem_cgroup *memcg, struct kmem_cache *s,
return -ENOMEM;

if (memcg) {
+ s->memcg_params->cachep = s;
s->memcg_params->memcg = memcg;
s->memcg_params->root_cache = root_cache;
INIT_WORK(&s->memcg_params->destroy,
@@ -3184,11 +3172,6 @@ void memcg_register_cache(struct kmem_cache *s)
*/
smp_wmb();

- /*
- * Initialize the pointer to this cache in its parent's memcg_params
- * before adding it to the memcg_slab_caches list, otherwise we can
- * fail to convert memcg_params_to_cache() while traversing the list.
- */
VM_BUG_ON(root->memcg_params->memcg_caches[id]);
root->memcg_params->memcg_caches[id] = s;

@@ -3220,11 +3203,6 @@ void memcg_unregister_cache(struct kmem_cache *s)
list_del(&s->memcg_params->list);
mutex_unlock(&memcg->slab_caches_mutex);

- /*
- * Clear the pointer to this cache in its parent's memcg_params only
- * after removing it from the memcg_slab_caches list, otherwise we can
- * fail to convert memcg_params_to_cache() while traversing the list.
- */
VM_BUG_ON(root->memcg_params->memcg_caches[id] != s);
root->memcg_params->memcg_caches[id] = NULL;
}
@@ -3266,7 +3244,7 @@ static void kmem_cache_destroy_work_func(struct work_struct *w)
struct memcg_cache_params *params;

params = container_of(w, struct memcg_cache_params, destroy);
- cachep = memcg_params_to_cache(params);
+ cachep = params->cachep;

if (atomic_read(&params->refcount) != 0) {
/*
--
1.7.10.4


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