[PATCH -mm 1/6] slab: embed memcg_cache_params to kmem_cache

From: Vladimir Davydov
Date: Fri Jan 16 2015 - 09:14:46 EST

Currently, kmem_cache stores a pointer to struct memcg_cache_params
instead of embedding it. The rationale is to save memory when kmem
accounting is disabled. However, the memcg_cache_params has shrivelled
drastically since it was first introduced:

* Initially:

struct memcg_cache_params {
bool is_root_cache;
union {
struct kmem_cache *memcg_caches[0];
struct {
struct mem_cgroup *memcg;
struct list_head list;
struct kmem_cache *root_cache;
bool dead;
atomic_t nr_pages;
struct work_struct destroy;
};
};
};

* Now:

struct memcg_cache_params {
bool is_root_cache;
union {
struct {
struct rcu_head rcu_head;
struct kmem_cache *memcg_caches[0];
};
struct {
struct mem_cgroup *memcg;
struct kmem_cache *root_cache;
};
};
};

So the memory saving does not seem to be a clear win anymore.

OTOH, keeping a pointer to memcg_cache_params struct instead of
embedding it results in touching one more cache line on kmem alloc/free
hot paths. Besides, it makes linking kmem caches in a list chained by a
field of struct memcg_cache_params really painful due to a level of
indirection, while I want to make them linked in the following patch.
That said, let us embed it.

Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
---
include/linux/slab.h | 17 +++----
include/linux/slab_def.h | 2 +-
include/linux/slub_def.h | 2 +-
mm/memcontrol.c | 11 ++--
mm/slab.h | 48 +++++++++---------
mm/slab_common.c | 126 +++++++++++++++++++++++++---------------------
mm/slub.c | 5 +-
7 files changed, 109 insertions(+), 102 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 2e3b448cfa2d..1e03c11bbfbd 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -473,14 +473,14 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
#ifndef ARCH_SLAB_MINALIGN
#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
#endif
+
+struct memcg_cache_array {
+ struct rcu_head rcu;
+ struct kmem_cache *entries[0];
+};
+
/*
* This is the main placeholder for memcg-related information in kmem caches.
- * struct kmem_cache will hold a pointer to it, so the memory cost while
- * disabled is 1 pointer. The runtime cost while enabled, gets bigger than it
- * would otherwise be if that would be bundled in kmem_cache: we'll need an
- * extra pointer chase. But the trade off clearly lays in favor of not
- * penalizing non-users.
- *
* Both the root cache and the child caches will have it. For the root cache,
* this will hold a dynamically allocated array large enough to hold
* information about the currently limited memcgs in the system. To allow the
@@ -495,10 +495,7 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
struct memcg_cache_params {
bool is_root_cache;
union {
- struct {
- struct rcu_head rcu_head;
- struct kmem_cache *memcg_caches[0];
- };
+ struct memcg_cache_array __rcu *memcg_caches;
struct {
struct mem_cgroup *memcg;
struct kmem_cache *root_cache;
diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
index b869d1662ba3..33d049066c3d 100644
--- a/include/linux/slab_def.h
+++ b/include/linux/slab_def.h
@@ -70,7 +70,7 @@ struct kmem_cache {
int obj_offset;
#endif /* CONFIG_DEBUG_SLAB */
#ifdef CONFIG_MEMCG_KMEM
- struct memcg_cache_params *memcg_params;
+ struct memcg_cache_params memcg_params;
#endif

struct kmem_cache_node *node[MAX_NUMNODES];
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index d82abd40a3c0..9abf04ed0999 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -85,7 +85,7 @@ struct kmem_cache {
struct kobject kobj; /* For sysfs */
#endif
#ifdef CONFIG_MEMCG_KMEM
- struct memcg_cache_params *memcg_params;
+ struct memcg_cache_params memcg_params;
int max_attr_size; /* for propagation, maximum size of a stored attr */
#ifdef CONFIG_SYSFS
struct kset *memcg_kset;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 825ef6a273e9..f03bd5b2797e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -345,7 +345,7 @@ struct mem_cgroup {
struct cg_proto tcp_mem;
#endif
#if defined(CONFIG_MEMCG_KMEM)
- /* Index in the kmem_cache->memcg_params->memcg_caches array */
+ /* Index in the kmem_cache->memcg_params.memcg_caches array */
int kmemcg_id;
#endif

@@ -557,7 +557,7 @@ static void disarm_sock_keys(struct mem_cgroup *memcg)

#ifdef CONFIG_MEMCG_KMEM
/*
- * This will be the memcg's index in each cache's ->memcg_params->memcg_caches.
+ * 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
@@ -2676,8 +2676,7 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep)
struct mem_cgroup *memcg;
struct kmem_cache *memcg_cachep;

- VM_BUG_ON(!cachep->memcg_params);
- VM_BUG_ON(!cachep->memcg_params->is_root_cache);
+ VM_BUG_ON(!is_root_cache(cachep));

if (current->memcg_kmem_skip_account)
return cachep;
@@ -2711,7 +2710,7 @@ out:
void __memcg_kmem_put_cache(struct kmem_cache *cachep)
{
if (!is_root_cache(cachep))
- css_put(&cachep->memcg_params->memcg->css);
+ css_put(&cachep->memcg_params.memcg->css);
}

/*
@@ -2787,7 +2786,7 @@ struct mem_cgroup *__mem_cgroup_from_kmem(void *ptr)
if (PageSlab(page)) {
cachep = page->slab_cache;
if (!is_root_cache(cachep))
- memcg = cachep->memcg_params->memcg;
+ memcg = cachep->memcg_params.memcg;
} else
/* page allocated by alloc_kmem_pages */
memcg = page->mem_cgroup;
diff --git a/mm/slab.h b/mm/slab.h
index 90430d6f665e..53a623f85931 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -86,8 +86,6 @@ extern struct kmem_cache *create_kmalloc_cache(const char *name, size_t size,
extern void create_boot_cache(struct kmem_cache *, const char *name,
size_t size, unsigned long flags);

-struct mem_cgroup;
-
int slab_unmergeable(struct kmem_cache *s);
struct kmem_cache *find_mergeable(size_t size, size_t align,
unsigned long flags, const char *name, void (*ctor)(void *));
@@ -167,14 +165,13 @@ ssize_t slabinfo_write(struct file *file, const char __user *buffer,
#ifdef CONFIG_MEMCG_KMEM
static inline bool is_root_cache(struct kmem_cache *s)
{
- return !s->memcg_params || s->memcg_params->is_root_cache;
+ return s->memcg_params.is_root_cache;
}

static inline bool slab_equal_or_root(struct kmem_cache *s,
- struct kmem_cache *p)
+ struct kmem_cache *p)
{
- return (p == s) ||
- (s->memcg_params && (p == s->memcg_params->root_cache));
+ return p == s || p == s->memcg_params.root_cache;
}

/*
@@ -185,37 +182,30 @@ static inline bool slab_equal_or_root(struct kmem_cache *s,
static inline const char *cache_name(struct kmem_cache *s)
{
if (!is_root_cache(s))
- return s->memcg_params->root_cache->name;
+ s = s->memcg_params.root_cache;
return s->name;
}

/*
* Note, we protect with RCU only the memcg_caches array, not per-memcg caches.
- * That said the caller must assure the memcg's cache won't go away. Since once
- * 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.
+ * That said the caller must assure the memcg's cache won't go away by either
+ * taking a css reference to the owner cgroup, or holding the slab_mutex.
*/
static inline struct kmem_cache *
cache_from_memcg_idx(struct kmem_cache *s, int idx)
{
struct kmem_cache *cachep;
- struct memcg_cache_params *params;
-
- if (!s->memcg_params)
- return NULL;
+ struct memcg_cache_array *arr;

rcu_read_lock();
- params = rcu_dereference(s->memcg_params);
+ arr = rcu_dereference(s->memcg_params.memcg_caches);

/*
* 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_create_kmem_cache()).
*/
- cachep = lockless_dereference(params->memcg_caches[idx]);
+ cachep = lockless_dereference(arr->entries[idx]);
rcu_read_unlock();

return cachep;
@@ -225,7 +215,7 @@ static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s)
{
if (is_root_cache(s))
return s;
- return s->memcg_params->root_cache;
+ return s->memcg_params.root_cache;
}

static __always_inline int memcg_charge_slab(struct kmem_cache *s,
@@ -235,7 +225,7 @@ static __always_inline int memcg_charge_slab(struct kmem_cache *s,
return 0;
if (is_root_cache(s))
return 0;
- return memcg_charge_kmem(s->memcg_params->memcg, gfp, 1 << order);
+ return memcg_charge_kmem(s->memcg_params.memcg, gfp, 1 << order);
}

static __always_inline void memcg_uncharge_slab(struct kmem_cache *s, int order)
@@ -244,9 +234,13 @@ static __always_inline void memcg_uncharge_slab(struct kmem_cache *s, int order)
return;
if (is_root_cache(s))
return;
- memcg_uncharge_kmem(s->memcg_params->memcg, 1 << order);
+ memcg_uncharge_kmem(s->memcg_params.memcg, 1 << order);
}
-#else
+
+extern void slab_init_memcg_params(struct kmem_cache *);
+
+#else /* !CONFIG_MEMCG_KMEM */
+
static inline bool is_root_cache(struct kmem_cache *s)
{
return true;
@@ -282,7 +276,11 @@ static inline int memcg_charge_slab(struct kmem_cache *s, gfp_t gfp, int order)
static inline void memcg_uncharge_slab(struct kmem_cache *s, int order)
{
}
-#endif
+
+static inline void slab_init_memcg_params(struct kmem_cache *s)
+{
+}
+#endif /* CONFIG_MEMCG_KMEM */

static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
{
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 42bb22cb4219..4f1492a9e2da 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -106,62 +106,65 @@ static inline int kmem_cache_sanity_check(const char *name, size_t size)
#endif

#ifdef CONFIG_MEMCG_KMEM
-static int memcg_alloc_cache_params(struct mem_cgroup *memcg,
- struct kmem_cache *s, struct kmem_cache *root_cache)
+void slab_init_memcg_params(struct kmem_cache *s)
{
- size_t size;
+ s->memcg_params.is_root_cache = true;
+ RCU_INIT_POINTER(s->memcg_params.memcg_caches, NULL);
+}
+
+static int init_memcg_params(struct kmem_cache *s,
+ struct mem_cgroup *memcg, struct kmem_cache *root_cache)
+{
+ struct memcg_cache_array *arr;

- if (!memcg_kmem_enabled())
+ if (memcg) {
+ s->memcg_params.is_root_cache = false;
+ s->memcg_params.memcg = memcg;
+ s->memcg_params.root_cache = root_cache;
return 0;
+ }

- if (!memcg) {
- size = offsetof(struct memcg_cache_params, memcg_caches);
- size += memcg_nr_cache_ids * sizeof(void *);
- } else
- size = sizeof(struct memcg_cache_params);
+ slab_init_memcg_params(s);

- s->memcg_params = kzalloc(size, GFP_KERNEL);
- if (!s->memcg_params)
- return -ENOMEM;
+ if (!memcg_nr_cache_ids)
+ return 0;

- if (memcg) {
- s->memcg_params->memcg = memcg;
- s->memcg_params->root_cache = root_cache;
- } else
- s->memcg_params->is_root_cache = true;
+ arr = kzalloc(sizeof(struct memcg_cache_array) +
+ memcg_nr_cache_ids * sizeof(void *),
+ GFP_KERNEL);
+ if (!arr)
+ return -ENOMEM;

+ RCU_INIT_POINTER(s->memcg_params.memcg_caches, arr);
return 0;
}

-static void memcg_free_cache_params(struct kmem_cache *s)
+static void destroy_memcg_params(struct kmem_cache *s)
{
- kfree(s->memcg_params);
+ if (is_root_cache(s))
+ kfree(rcu_access_pointer(s->memcg_params.memcg_caches));
}

-static int memcg_update_cache_params(struct kmem_cache *s, int num_memcgs)
+static int update_memcg_params(struct kmem_cache *s, int new_array_size)
{
- int size;
- struct memcg_cache_params *new_params, *cur_params;
+ struct memcg_cache_array *old, *new;

- BUG_ON(!is_root_cache(s));
-
- size = offsetof(struct memcg_cache_params, memcg_caches);
- size += num_memcgs * sizeof(void *);
+ if (!is_root_cache(s))
+ return 0;

- new_params = kzalloc(size, GFP_KERNEL);
- if (!new_params)
+ old = rcu_dereference_protected(s->memcg_params.memcg_caches,
+ lockdep_is_held(&slab_mutex));
+ new = kzalloc(sizeof(struct memcg_cache_array) +
+ new_array_size * sizeof(void *), GFP_KERNEL);
+ if (!new)
return -ENOMEM;

- cur_params = s->memcg_params;
- memcpy(new_params->memcg_caches, cur_params->memcg_caches,
+ memcpy(new->entries, old->entries,
memcg_nr_cache_ids * sizeof(void *));

- new_params->is_root_cache = true;
-
- rcu_assign_pointer(s->memcg_params, new_params);
- if (cur_params)
- kfree_rcu(cur_params, rcu_head);
-
+ rcu_assign_pointer(s->memcg_params.memcg_caches, new);
+ if (old)
+ kfree_rcu(old, rcu);
return 0;
}

@@ -172,10 +175,7 @@ int memcg_update_all_caches(int num_memcgs)

mutex_lock(&slab_mutex);
list_for_each_entry(s, &slab_caches, list) {
- if (!is_root_cache(s))
- continue;
-
- ret = memcg_update_cache_params(s, num_memcgs);
+ ret = update_memcg_params(s, num_memcgs);
/*
* Instead of freeing the memory, we'll just leave the caches
* up to this point in an updated state.
@@ -187,13 +187,13 @@ int memcg_update_all_caches(int num_memcgs)
return ret;
}
#else
-static inline int memcg_alloc_cache_params(struct mem_cgroup *memcg,
- struct kmem_cache *s, struct kmem_cache *root_cache)
+static inline int init_memcg_params(struct kmem_cache *s,
+ struct mem_cgroup *memcg, struct kmem_cache *root_cache)
{
return 0;
}

-static inline void memcg_free_cache_params(struct kmem_cache *s)
+static inline void destroy_memcg_params(struct kmem_cache *s)
{
}
#endif /* CONFIG_MEMCG_KMEM */
@@ -311,7 +311,7 @@ do_kmem_cache_create(char *name, size_t object_size, size_t size, size_t align,
s->align = align;
s->ctor = ctor;

- err = memcg_alloc_cache_params(memcg, s, root_cache);
+ err = init_memcg_params(s, memcg, root_cache);
if (err)
goto out_free_cache;

@@ -327,7 +327,7 @@ out:
return s;

out_free_cache:
- memcg_free_cache_params(s);
+ destroy_memcg_params(s);
kfree(s);
goto out;
}
@@ -439,11 +439,15 @@ static int do_kmem_cache_shutdown(struct kmem_cache *s,

#ifdef CONFIG_MEMCG_KMEM
if (!is_root_cache(s)) {
- struct kmem_cache *root_cache = s->memcg_params->root_cache;
- int memcg_id = memcg_cache_id(s->memcg_params->memcg);
-
- BUG_ON(root_cache->memcg_params->memcg_caches[memcg_id] != s);
- root_cache->memcg_params->memcg_caches[memcg_id] = NULL;
+ 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;
}
#endif
list_move(&s->list, release);
@@ -481,27 +485,32 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
struct kmem_cache *root_cache)
{
static char memcg_name_buf[NAME_MAX + 1]; /* protected by slab_mutex */
- int memcg_id = memcg_cache_id(memcg);
+ struct memcg_cache_array *arr;
struct kmem_cache *s = NULL;
char *cache_name;
+ int idx;

get_online_cpus();
get_online_mems();

mutex_lock(&slab_mutex);

+ idx = memcg_cache_id(memcg);
+ arr = rcu_dereference_protected(root_cache->memcg_params.memcg_caches,
+ lockdep_is_held(&slab_mutex));
+
/*
* 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, memcg_id))
+ if (arr->entries[idx])
goto out_unlock;

cgroup_name(mem_cgroup_css(memcg)->cgroup,
memcg_name_buf, sizeof(memcg_name_buf));
cache_name = kasprintf(GFP_KERNEL, "%s(%d:%s)", root_cache->name,
- memcg_cache_id(memcg), memcg_name_buf);
+ idx, memcg_name_buf);
if (!cache_name)
goto out_unlock;

@@ -525,7 +534,7 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
* initialized.
*/
smp_wmb();
- root_cache->memcg_params->memcg_caches[memcg_id] = s;
+ arr->entries[idx] = s;

out_unlock:
mutex_unlock(&slab_mutex);
@@ -545,7 +554,7 @@ void memcg_destroy_kmem_caches(struct mem_cgroup *memcg)

mutex_lock(&slab_mutex);
list_for_each_entry_safe(s, s2, &slab_caches, list) {
- if (is_root_cache(s) || s->memcg_params->memcg != memcg)
+ if (is_root_cache(s) || s->memcg_params.memcg != memcg)
continue;
/*
* The cgroup is about to be freed and therefore has no charges
@@ -564,7 +573,7 @@ void memcg_destroy_kmem_caches(struct mem_cgroup *memcg)

void slab_kmem_cache_release(struct kmem_cache *s)
{
- memcg_free_cache_params(s);
+ destroy_memcg_params(s);
kfree(s->name);
kmem_cache_free(kmem_cache, s);
}
@@ -640,6 +649,9 @@ void __init create_boot_cache(struct kmem_cache *s, const char *name, size_t siz
s->name = name;
s->size = s->object_size = size;
s->align = calculate_alignment(flags, ARCH_KMALLOC_MINALIGN, size);
+
+ slab_init_memcg_params(s);
+
err = __kmem_cache_create(s, flags);

if (err)
@@ -980,7 +992,7 @@ int memcg_slab_show(struct seq_file *m, void *p)

if (p == slab_caches.next)
print_slabinfo_header(m);
- if (!is_root_cache(s) && s->memcg_params->memcg == memcg)
+ if (!is_root_cache(s) && s->memcg_params.memcg == memcg)
cache_show(s, m);
return 0;
}
diff --git a/mm/slub.c b/mm/slub.c
index fe376fe1f4fe..84f8b7446558 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3566,6 +3566,7 @@ static struct kmem_cache * __init bootstrap(struct kmem_cache *static_cache)
p->slab_cache = s;
#endif
}
+ slab_init_memcg_params(s);
list_add(&s->list, &slab_caches);
return s;
}
@@ -4953,7 +4954,7 @@ static void memcg_propagate_slab_attrs(struct kmem_cache *s)
if (is_root_cache(s))
return;

- root_cache = s->memcg_params->root_cache;
+ root_cache = s->memcg_params.root_cache;

/*
* This mean this cache had no attribute written. Therefore, no point
@@ -5033,7 +5034,7 @@ static inline struct kset *cache_kset(struct kmem_cache *s)
{
#ifdef CONFIG_MEMCG_KMEM
if (!is_root_cache(s))
- return s->memcg_params->root_cache->memcg_kset;
+ return s->memcg_params.root_cache->memcg_kset;
#endif
return slab_kset;
}
--
1.7.10.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/