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Subject[PATCH -mm v2 5/7] memcg: free memcg_caches slot on css offline
Date
We need to look up a kmem_cache in ->memcg_params.memcg_caches arrays
only on allocations, so there is no need to have the array entries set
until css free - we can clear them on css offline. This will allow us to
reuse array entries more efficiently and avoid costly array relocations.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
---
include/linux/slab.h | 10 +++++-----
mm/memcontrol.c | 38 ++++++++++++++++++++++++++++++++------
mm/slab_common.c | 39 ++++++++++++++++++++++++++++-----------
3 files changed, 65 insertions(+), 22 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 26d99f41b410..ed2ffaab59ea 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -115,13 +115,12 @@ int slab_is_available(void);
struct kmem_cache *kmem_cache_create(const char *, size_t, size_t,
unsigned long,
void (*)(void *));
-#ifdef CONFIG_MEMCG_KMEM
-void memcg_create_kmem_cache(struct mem_cgroup *, struct kmem_cache *);
-void memcg_destroy_kmem_caches(struct mem_cgroup *);
-#endif
void kmem_cache_destroy(struct kmem_cache *);
int kmem_cache_shrink(struct kmem_cache *);
-void kmem_cache_free(struct kmem_cache *, void *);
+
+void memcg_create_kmem_cache(struct mem_cgroup *, struct kmem_cache *);
+void memcg_deactivate_kmem_caches(struct mem_cgroup *);
+void memcg_destroy_kmem_caches(struct mem_cgroup *);

/*
* Please use this macro to create slab caches. Simply specify the
@@ -288,6 +287,7 @@ static __always_inline int kmalloc_index(size_t size)

void *__kmalloc(size_t size, gfp_t flags);
void *kmem_cache_alloc(struct kmem_cache *, gfp_t flags);
+void kmem_cache_free(struct kmem_cache *, void *);

#ifdef CONFIG_NUMA
void *__kmalloc_node(size_t size, gfp_t flags, int node);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c502f1a92daf..0875217ceb68 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -334,6 +334,7 @@ struct mem_cgroup {
#if defined(CONFIG_MEMCG_KMEM)
/* Index in the kmem_cache->memcg_params.memcg_caches array */
int kmemcg_id;
+ bool kmem_acct_active;
#endif

int last_scanned_node;
@@ -354,7 +355,7 @@ struct mem_cgroup {
#ifdef CONFIG_MEMCG_KMEM
bool memcg_kmem_is_active(struct mem_cgroup *memcg)
{
- return memcg->kmemcg_id >= 0;
+ return memcg->kmem_acct_active;
}
#endif

@@ -585,7 +586,7 @@ static void memcg_free_cache_id(int id);

static void disarm_kmem_keys(struct mem_cgroup *memcg)
{
- if (memcg_kmem_is_active(memcg)) {
+ if (memcg->kmemcg_id >= 0) {
static_key_slow_dec(&memcg_kmem_enabled_key);
memcg_free_cache_id(memcg->kmemcg_id);
}
@@ -2672,6 +2673,7 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep)
{
struct mem_cgroup *memcg;
struct kmem_cache *memcg_cachep;
+ int kmemcg_id;

VM_BUG_ON(!is_root_cache(cachep));

@@ -2679,10 +2681,11 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep)
return cachep;

memcg = get_mem_cgroup_from_mm(current->mm);
- if (!memcg_kmem_is_active(memcg))
+ kmemcg_id = ACCESS_ONCE(memcg->kmemcg_id);
+ if (kmemcg_id < 0)
goto out;

- memcg_cachep = cache_from_memcg_idx(cachep, memcg_cache_id(memcg));
+ memcg_cachep = cache_from_memcg_idx(cachep, kmemcg_id);
if (likely(memcg_cachep))
return memcg_cachep;

@@ -3324,8 +3327,8 @@ static int memcg_activate_kmem(struct mem_cgroup *memcg,
int err = 0;
int memcg_id;

- if (memcg_kmem_is_active(memcg))
- return 0;
+ BUG_ON(memcg->kmemcg_id >= 0);
+ BUG_ON(memcg->kmem_acct_active);

/*
* For simplicity, we won't allow this to be disabled. It also can't
@@ -3368,6 +3371,7 @@ static int memcg_activate_kmem(struct mem_cgroup *memcg,
* patched.
*/
memcg->kmemcg_id = memcg_id;
+ memcg->kmem_acct_active = true;
out:
return err;
}
@@ -4055,6 +4059,22 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
return mem_cgroup_sockets_init(memcg, ss);
}

+static void memcg_deactivate_kmem(struct mem_cgroup *memcg)
+{
+ if (!memcg->kmem_acct_active)
+ return;
+
+ /*
+ * Clear the 'active' flag before clearing memcg_caches arrays entries.
+ * Since we take the slab_mutex in memcg_deactivate_kmem_caches(), it
+ * guarantees no cache will be created for this cgroup after we are
+ * done (see memcg_create_kmem_cache()).
+ */
+ memcg->kmem_acct_active = false;
+
+ memcg_deactivate_kmem_caches(memcg);
+}
+
static void memcg_destroy_kmem(struct mem_cgroup *memcg)
{
memcg_destroy_kmem_caches(memcg);
@@ -4066,6 +4086,10 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
return 0;
}

+static void memcg_deactivate_kmem(struct mem_cgroup *memcg)
+{
+}
+
static void memcg_destroy_kmem(struct mem_cgroup *memcg)
{
}
@@ -4622,6 +4646,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
spin_unlock(&memcg->event_list_lock);

vmpressure_cleanup(&memcg->vmpressure);
+
+ memcg_deactivate_kmem(memcg);
}

static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 7f90acf3a3ff..bf4a42b2c5ba 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -439,18 +439,8 @@ static int do_kmem_cache_shutdown(struct kmem_cache *s,
*need_rcu_barrier = true;

#ifdef CONFIG_MEMCG_KMEM
- if (!is_root_cache(s)) {
- int idx;
- struct memcg_cache_array *arr;
-
- idx = memcg_cache_id(s->memcg_params.memcg);
- arr = rcu_dereference_protected(s->memcg_params.root_cache->
- memcg_params.memcg_caches,
- lockdep_is_held(&slab_mutex));
- BUG_ON(arr->entries[idx] != s);
- arr->entries[idx] = NULL;
+ if (!is_root_cache(s))
list_del(&s->memcg_params.list);
- }
#endif
list_move(&s->list, release);
return 0;
@@ -498,6 +488,13 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,

mutex_lock(&slab_mutex);

+ /*
+ * The memory cgroup could have been deactivated while the cache
+ * creation work was pending.
+ */
+ if (!memcg_kmem_is_active(memcg))
+ goto out_unlock;
+
idx = memcg_cache_id(memcg);
arr = rcu_dereference_protected(root_cache->memcg_params.memcg_caches,
lockdep_is_held(&slab_mutex));
@@ -547,6 +544,26 @@ out_unlock:
put_online_cpus();
}

+void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
+{
+ int idx;
+ struct memcg_cache_array *arr;
+ struct kmem_cache *s;
+
+ idx = memcg_cache_id(memcg);
+
+ mutex_lock(&slab_mutex);
+ list_for_each_entry(s, &slab_caches, list) {
+ if (!is_root_cache(s))
+ continue;
+
+ arr = rcu_dereference_protected(s->memcg_params.memcg_caches,
+ lockdep_is_held(&slab_mutex));
+ arr->entries[idx] = NULL;
+ }
+ mutex_unlock(&slab_mutex);
+}
+
void memcg_destroy_kmem_caches(struct mem_cgroup *memcg)
{
LIST_HEAD(release);
--
1.7.10.4


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