[PATCH -mm v2 6/6] memcg: cleanup kmem_id-related naming

From: Vladimir Davydov
Date: Sun Apr 27 2014 - 05:04:52 EST

The naming of mem_cgroup->kmemcg_id-related functions is rather
inconsistent. We tend to use cache_id as part of their names, but it
isn't quite right, because kmem_id isn't something specific to kmem
caches. It can be used for indexing any array that stores per memcg
data. For instance, we will use it to make list_lru per memcg in the
future. So let's clean up the names and comments related to kmem_id.

Brief change log:

** old name ** ** new name **

mem_cgroup->kmemcg_id mem_cgroup->kmem_id

memcg_init_cache_id() memcg_init_kmem_id()
memcg_cache_id() memcg_kmem_id()
cache_from_memcg_idx() kmem_cache_of_memcg_by_id()
cache_from_memcg_idx(memcg_cache_id()) kmem_cache_of_memcg()

for_each_memcg_cache_index() for_each_possible_memcg_kmem_id()

memcg_limited_groups memcg_kmem_ida
memcg_limited_groups_array_size memcg_nr_kmem_ids_max

MEMCG_CACHES_MIN_SIZE <constant inlined>
MEMCG_CACHES_MAX_SIZE MEMCG_KMEM_ID_MAX + 1

Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
---
include/linux/memcontrol.h | 19 +++----
mm/memcontrol.c | 117 +++++++++++++++++++++-----------------------
mm/slab.c | 4 +-
mm/slab.h | 24 ++++++---
mm/slab_common.c | 10 ++--
mm/slub.c | 10 ++--
6 files changed, 93 insertions(+), 91 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index b20f533a92ca..1a5c33fd40a4 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -458,15 +458,10 @@ static inline void sock_release_memcg(struct sock *sk)
#ifdef CONFIG_MEMCG_KMEM
extern struct static_key memcg_kmem_enabled_key;

-extern int memcg_limited_groups_array_size;
+extern int memcg_nr_kmem_ids_max;

-/*
- * Helper macro to loop through all memcg-specific caches. Callers must still
- * check if the cache is valid (it is either valid or NULL).
- * the slab_mutex must be held when looping through those caches
- */
-#define for_each_memcg_cache_index(_idx) \
- for ((_idx) = 0; (_idx) < memcg_limited_groups_array_size; (_idx)++)
+#define for_each_possible_memcg_kmem_id(id) \
+ for ((id) = 0; (id) < memcg_nr_kmem_ids_max; (id)++)

static inline bool memcg_kmem_enabled(void)
{
@@ -490,7 +485,7 @@ void __memcg_kmem_commit_charge(struct page *page,
struct mem_cgroup *memcg, int order);
void __memcg_kmem_uncharge_pages(struct page *page, int order);

-int memcg_cache_id(struct mem_cgroup *memcg);
+int memcg_kmem_id(struct mem_cgroup *memcg);

struct kmem_cache *
__memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp);
@@ -591,8 +586,8 @@ memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp)
return __memcg_kmem_get_cache(cachep, gfp);
}
#else
-#define for_each_memcg_cache_index(_idx) \
- for (; NULL; )
+#define for_each_possible_memcg_kmem_id(id) \
+ for ((id) = 0; 0; )

static inline bool memcg_kmem_enabled(void)
{
@@ -614,7 +609,7 @@ memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, int order)
{
}

-static inline int memcg_cache_id(struct mem_cgroup *memcg)
+static inline int memcg_kmem_id(struct mem_cgroup *memcg)
{
return -1;
}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c795c3e388dc..1077091e995f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -357,11 +357,22 @@ struct mem_cgroup {
struct cg_proto tcp_mem;
#endif
#if defined(CONFIG_MEMCG_KMEM)
+ /*
+ * Each kmem-limited memory cgroup has a unique id. We use it for
+ * indexing the arrays that store per cgroup data. An example of such
+ * an array is kmem_cache->memcg_params->memcg_caches.
+ *
+ * We introduce a separate id instead of using cgroup->id to avoid
+ * waste of memory in sparse environments, where we have a lot of
+ * memory cgroups, but only a few of them are kmem-limited.
+ *
+ * For unlimited cgroups kmem_id equals -1.
+ */
+ int kmem_id;
+
/* analogous to slab_common's slab_caches list, but per-memcg;
* protected by memcg_slab_mutex */
struct list_head memcg_slab_caches;
- /* Index in the kmem_cache->memcg_params->memcg_caches array */
- int kmemcg_id;
#endif

int last_scanned_node;
@@ -610,35 +621,28 @@ static void disarm_sock_keys(struct mem_cgroup *memcg)
#endif

#ifdef CONFIG_MEMCG_KMEM
+/* used for mem_cgroup->kmem_id allocations */
+static DEFINE_IDA(memcg_kmem_ida);
+
/*
- * This will be the memcg's index in each cache's ->memcg_params->memcg_caches.
- * The main reason for not using cgroup id for this:
- * this works better in sparse environments, where we have a lot of memcgs,
- * but only a few kmem-limited. Or also, if we have, for instance, 200
- * memcgs, and none but the 200th is kmem-limited, we'd have to have a
- * 200 entry array for that.
- *
- * The current size of the caches array is stored in
- * memcg_limited_groups_array_size. It will double each time we have to
- * increase it.
+ * Max kmem id should be as large as max cgroup id so that we could enable
+ * kmem-accounting for each memory cgroup.
*/
-static DEFINE_IDA(kmem_limited_groups);
-int memcg_limited_groups_array_size;
+#define MEMCG_KMEM_ID_MAX MEM_CGROUP_ID_MAX

/*
- * MIN_SIZE is different than 1, because we would like to avoid going through
- * the alloc/free process all the time. In a small machine, 4 kmem-limited
- * cgroups is a reasonable guess. In the future, it could be a parameter or
- * tunable, but that is strictly not necessary.
+ * We keep the maximal number of kmem ids that may exist in the system in the
+ * memcg_nr_kmem_ids_max variable. We use it for the size of the arrays indexed
+ * by kmem id (see the mem_cgroup->kmem_id definition).
+ *
+ * If a newly allocated kmem id is greater or equal to memcg_nr_kmem_ids_max,
+ * we double it and reallocate the arrays so that they have enough space to
+ * store data for the new cgroup.
*
- * MAX_SIZE should be as large as the number of cgrp_ids. Ideally, we could get
- * this constant directly from cgroup, but it is understandable that this is
- * better kept as an internal representation in cgroup.c. In any case, the
- * cgrp_id space is not getting any smaller, and we don't have to necessarily
- * increase ours as well if it increases.
+ * The updates are done with activate_kmem_mutex held, so one must take it to
+ * guarantee a stable value of memcg_nr_kmem_ids_max.
*/
-#define MEMCG_CACHES_MIN_SIZE 4
-#define MEMCG_CACHES_MAX_SIZE MEM_CGROUP_ID_MAX
+int memcg_nr_kmem_ids_max;

/*
* A lot of the calls to the cache allocation functions are expected to be
@@ -653,7 +657,7 @@ static void disarm_kmem_keys(struct mem_cgroup *memcg)
{
if (memcg_kmem_is_active(memcg)) {
static_key_slow_dec(&memcg_kmem_enabled_key);
- ida_simple_remove(&kmem_limited_groups, memcg->kmemcg_id);
+ ida_simple_remove(&memcg_kmem_ida, memcg->kmem_id);
}
/*
* This check can't live in kmem destruction function,
@@ -2930,11 +2934,8 @@ static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
*/
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));
+ return kmem_cache_of_memcg(p->root_cache, p->memcg);
}

#ifdef CONFIG_SLABINFO
@@ -3017,29 +3018,24 @@ static void memcg_uncharge_kmem(struct mem_cgroup *memcg, u64 size)
css_put(&memcg->css);
}

-/*
- * helper for acessing a memcg's index. It will be used as an index in the
- * child cache array in kmem_cache, and also to derive its name. This function
- * will return -1 when this is not a kmem-limited memcg.
- */
-int memcg_cache_id(struct mem_cgroup *memcg)
+int memcg_kmem_id(struct mem_cgroup *memcg)
{
- return memcg ? memcg->kmemcg_id : -1;
+ return memcg ? memcg->kmem_id : -1;
}

-static int memcg_init_cache_id(struct mem_cgroup *memcg)
+static int memcg_init_kmem_id(struct mem_cgroup *memcg)
{
int err = 0;
int id, size;

lockdep_assert_held(&activate_kmem_mutex);

- id = ida_simple_get(&kmem_limited_groups,
- 0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL);
+ id = ida_simple_get(&memcg_kmem_ida,
+ 0, MEMCG_KMEM_ID_MAX + 1, GFP_KERNEL);
if (id < 0)
return id;

- if (id < memcg_limited_groups_array_size)
+ if (id < memcg_nr_kmem_ids_max)
goto out_setid;

/*
@@ -3047,10 +3043,10 @@ static int memcg_init_cache_id(struct mem_cgroup *memcg)
* per memcg data. Let's try to grow them then.
*/
size = id * 2;
- if (size < MEMCG_CACHES_MIN_SIZE)
- size = MEMCG_CACHES_MIN_SIZE;
- else if (size > MEMCG_CACHES_MAX_SIZE)
- size = MEMCG_CACHES_MAX_SIZE;
+ if (size < 4)
+ size = 4; /* a good number to start with */
+ if (size > MEMCG_KMEM_ID_MAX + 1)
+ size = MEMCG_KMEM_ID_MAX + 1;

mutex_lock(&memcg_slab_mutex);
err = kmem_cache_memcg_arrays_grow(size);
@@ -3064,14 +3060,14 @@ static int memcg_init_cache_id(struct mem_cgroup *memcg)
* walking over such an array won't get an index out of range provided
* they use an appropriate mutex to protect the array's elements.
*/
- memcg_limited_groups_array_size = size;
+ memcg_nr_kmem_ids_max = size;

out_setid:
- memcg->kmemcg_id = id;
+ memcg->kmem_id = id;
return 0;

out_rmid:
- ida_simple_remove(&kmem_limited_groups, id);
+ ida_simple_remove(&memcg_kmem_ida, id);
return err;
}

@@ -3089,11 +3085,10 @@ static int memcg_prepare_kmem_cache(struct kmem_cache *cachep)
return 0;

/* activate_kmem_mutex guarantees a stable value of
- * memcg_limited_groups_array_size */
+ * memcg_nr_kmem_ids_max */
mutex_lock(&activate_kmem_mutex);
mutex_lock(&memcg_slab_mutex);
- ret = kmem_cache_init_memcg_array(cachep,
- memcg_limited_groups_array_size);
+ ret = kmem_cache_init_memcg_array(cachep, memcg_nr_kmem_ids_max);
mutex_unlock(&memcg_slab_mutex);
mutex_unlock(&activate_kmem_mutex);
return ret;
@@ -3112,14 +3107,14 @@ static void memcg_copy_kmem_cache(struct mem_cgroup *memcg,

lockdep_assert_held(&memcg_slab_mutex);

- id = memcg_cache_id(memcg);
+ id = memcg_kmem_id(memcg);

/*
* Since per-memcg caches are created asynchronously on first
* allocation (see memcg_kmem_get_cache()), several threads can try to
* create the same cache, but only one of them may succeed.
*/
- if (cache_from_memcg_idx(root_cache, id))
+ if (kmem_cache_of_memcg_by_id(root_cache, id))
return;

cgroup_name(memcg->css.cgroup, memcg_name, NAME_MAX + 1);
@@ -3136,8 +3131,8 @@ static void memcg_copy_kmem_cache(struct mem_cgroup *memcg,
list_add(&cachep->memcg_params->list, &memcg->memcg_slab_caches);

/*
- * Since readers won't lock (see cache_from_memcg_idx()), we need a
- * barrier here to ensure nobody will see the kmem_cache partially
+ * Since readers won't lock (see kmem_cache_of_memcg_by_id()), we need
+ * a barrier here to ensure nobody will see the kmem_cache partially
* initialized.
*/
smp_wmb();
@@ -3159,7 +3154,7 @@ static int memcg_destroy_kmem_cache_copy(struct kmem_cache *cachep)

root_cache = cachep->memcg_params->root_cache;
memcg = cachep->memcg_params->memcg;
- id = memcg_cache_id(memcg);
+ id = memcg_kmem_id(memcg);

/*
* Since memcg_caches arrays can be accessed using only slab_mutex for
@@ -3226,8 +3221,8 @@ int __kmem_cache_destroy_memcg_copies(struct kmem_cache *cachep)
BUG_ON(!is_root_cache(cachep));

mutex_lock(&memcg_slab_mutex);
- for_each_memcg_cache_index(i) {
- c = cache_from_memcg_idx(cachep, i);
+ for_each_possible_memcg_kmem_id(i) {
+ c = kmem_cache_of_memcg_by_id(cachep, i);
if (!c)
continue;

@@ -3371,7 +3366,7 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep,
if (!memcg_can_account_kmem(memcg))
goto out;

- memcg_cachep = cache_from_memcg_idx(cachep, memcg_cache_id(memcg));
+ memcg_cachep = kmem_cache_of_memcg(cachep, memcg);
if (likely(memcg_cachep)) {
cachep = memcg_cachep;
goto out;
@@ -4945,7 +4940,7 @@ static int __memcg_activate_kmem(struct mem_cgroup *memcg,
if (err)
goto out;

- err = memcg_init_cache_id(memcg);
+ err = memcg_init_kmem_id(memcg);
if (err)
goto out;

@@ -5676,7 +5671,7 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
{
int ret;

- memcg->kmemcg_id = -1;
+ memcg->kmem_id = -1;
ret = memcg_propagate_kmem(memcg);
if (ret)
return ret;
diff --git a/mm/slab.c b/mm/slab.c
index 25317fd1daa2..194322a634e2 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3844,8 +3844,8 @@ static int do_tune_cpucache(struct kmem_cache *cachep, int limit,
return ret;

VM_BUG_ON(!mutex_is_locked(&slab_mutex));
- for_each_memcg_cache_index(i) {
- c = cache_from_memcg_idx(cachep, i);
+ for_each_possible_memcg_kmem_id(i) {
+ c = kmem_cache_of_memcg_by_id(cachep, i);
if (c)
/* return value determined by the parent cache only */
__do_tune_cpucache(c, limit, batchcount, shared, gfp);
diff --git a/mm/slab.h b/mm/slab.h
index ba834860fbfd..61f833c569e7 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -145,11 +145,11 @@ static inline const char *cache_name(struct kmem_cache *s)
* created a memcg's cache is destroyed only along with the root cache, it is
* true if we are going to allocate from the cache or hold a reference to the
* root cache by other means. Otherwise, we should hold either the slab_mutex
- * or the memcg's slab_caches_mutex while calling this function and accessing
- * the returned value.
+ * or the memcg_slab_mutex while calling this function and accessing the
+ * returned value.
*/
static inline struct kmem_cache *
-cache_from_memcg_idx(struct kmem_cache *s, int idx)
+kmem_cache_of_memcg_by_id(struct kmem_cache *s, int id)
{
struct kmem_cache *cachep;
struct memcg_cache_params *params;
@@ -159,18 +159,24 @@ cache_from_memcg_idx(struct kmem_cache *s, int idx)

rcu_read_lock();
params = rcu_dereference(s->memcg_params);
- cachep = params->memcg_caches[idx];
+ cachep = params->memcg_caches[id];
rcu_read_unlock();

/*
* Make sure we will access the up-to-date value. The code updating
* memcg_caches issues a write barrier to match this (see
- * memcg_register_cache()).
+ * memcg_copy_kmem_cache()).
*/
smp_read_barrier_depends();
return cachep;
}

+static inline struct kmem_cache *
+kmem_cache_of_memcg(struct kmem_cache *s, struct mem_cgroup *memcg)
+{
+ return kmem_cache_of_memcg_by_id(s, memcg_kmem_id(memcg));
+}
+
static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)
{
if (is_root_cache(s))
@@ -214,7 +220,13 @@ static inline const char *cache_name(struct kmem_cache *s)
}

static inline struct kmem_cache *
-cache_from_memcg_idx(struct kmem_cache *s, int idx)
+kmem_cache_of_memcg_by_id(struct kmem_cache *s, int id)
+{
+ return NULL;
+}
+
+static inline struct kmem_cache *
+kmem_cache_of_memcg(struct kmem_cache *s, struct mem_cgroup *memcg)
{
return NULL;
}
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 36c7d32a6f97..876b40bfe360 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -98,11 +98,11 @@ static int __kmem_cache_init_memcg_array(struct kmem_cache *s, int nr_entries)

new->is_root_cache = true;
if (old) {
- for_each_memcg_cache_index(i)
+ for_each_possible_memcg_kmem_id(i)
new->memcg_caches[i] = old->memcg_caches[i];
}

- /* matching rcu_dereference is in cache_from_memcg_idx */
+ /* matching rcu_dereference is in kmem_cache_of_memcg_by_id */
rcu_assign_pointer(s->memcg_params, new);
if (old)
kfree_rcu(old, rcu_head);
@@ -332,7 +332,7 @@ struct kmem_cache *kmem_cache_request_memcg_copy(struct kmem_cache *cachep,
memcg_params->root_cache = cachep;

cache_name = kasprintf(GFP_KERNEL, "%s(%d:%s)", cachep->name,
- memcg_cache_id(memcg), memcg_name);
+ memcg_kmem_id(memcg), memcg_name);
if (!cache_name)
goto out_unlock;

@@ -755,8 +755,8 @@ memcg_accumulate_slabinfo(struct kmem_cache *s, struct slabinfo *info)
if (!is_root_cache(s))
return;

- for_each_memcg_cache_index(i) {
- c = cache_from_memcg_idx(s, i);
+ for_each_possible_memcg_kmem_id(i) {
+ c = kmem_cache_of_memcg_by_id(s, i);
if (!c)
continue;

diff --git a/mm/slub.c b/mm/slub.c
index aa30932c5190..006e6bfe257c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3772,8 +3772,8 @@ __kmem_cache_alias(const char *name, size_t size, size_t align,
s->object_size = max(s->object_size, (int)size);
s->inuse = max_t(int, s->inuse, ALIGN(size, sizeof(void *)));

- for_each_memcg_cache_index(i) {
- c = cache_from_memcg_idx(s, i);
+ for_each_possible_memcg_kmem_id(i) {
+ c = kmem_cache_of_memcg_by_id(s, i);
if (!c)
continue;
c->object_size = s->object_size;
@@ -5062,8 +5062,8 @@ static ssize_t slab_attr_store(struct kobject *kobj,
* directly either failed or succeeded, in which case we loop
* through the descendants with best-effort propagation.
*/
- for_each_memcg_cache_index(i) {
- struct kmem_cache *c = cache_from_memcg_idx(s, i);
+ for_each_possible_memcg_kmem_id(i) {
+ struct kmem_cache *c = kmem_cache_of_memcg_by_id(s, i);
if (c)
attribute->store(c, buf, len);
}
@@ -5198,7 +5198,7 @@ static char *create_unique_id(struct kmem_cache *s)
#ifdef CONFIG_MEMCG_KMEM
if (!is_root_cache(s))
p += sprintf(p, "-%08d",
- memcg_cache_id(s->memcg_params->memcg));
+ memcg_kmem_id(s->memcg_params->memcg));
#endif

BUG_ON(p > name + ID_STR_LENGTH - 1);
--
1.7.10.4

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