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Subject[PATCH v3 06/16] memcg: infrastructure to match an allocation to the right cache
Date
The page allocator is able to bind a page to a memcg when it is
allocated. But for the caches, we'd like to have as many objects as
possible in a page belonging to the same cache.

This is done in this patch by calling memcg_kmem_get_cache in the
beginning of every allocation function. This routing is patched out by
static branches when kernel memory controller is not being used.

It assumes that the task allocating, which determines the memcg in the
page allocator, belongs to the same cgroup throughout the whole process.
Misacounting can happen if the task calls memcg_kmem_get_cache() while
belonging to a cgroup, and later on changes. This is considered
acceptable, and should only happen upon task migration.

Before the cache is created by the memcg core, there is also a possible
imbalance: the task belongs to a memcg, but the cache being allocated
from is the global cache, since the child cache is not yet guaranteed to
be ready. This case is also fine, since in this case the GFP_KMEMCG will
not be passed and the page allocator will not attempt any cgroup
accounting.

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>
---
include/linux/memcontrol.h | 38 +++++++++
init/Kconfig | 2 +-
mm/memcontrol.c | 203 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 242 insertions(+), 1 deletion(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index a5f3055..c44a5f2 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -419,6 +419,8 @@ extern void memcg_init_kmem_cache(void);
extern void memcg_register_cache(struct mem_cgroup *memcg,
struct kmem_cache *s);
extern void memcg_release_cache(struct kmem_cache *cachep);
+struct kmem_cache *
+__memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp);
#else

static inline void memcg_init_kmem_cache(void)
@@ -460,6 +462,12 @@ static inline void
__memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, int order)
{
}
+
+static inline struct kmem_cache *
+__memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp)
+{
+ return cachep;
+}
#endif /* CONFIG_MEMCG_KMEM */

/**
@@ -526,5 +534,35 @@ memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, int order)
if (memcg_kmem_enabled() && memcg)
__memcg_kmem_commit_charge(page, memcg, order);
}
+
+/**
+ * memcg_kmem_get_kmem_cache: selects the correct per-memcg cache for allocation
+ * @cachep: the original global kmem cache
+ * @gfp: allocation flags.
+ *
+ * This function assumes that the task allocating, which determines the memcg
+ * in the page allocator, belongs to the same cgroup throughout the whole
+ * process. Misacounting can happen if the task calls memcg_kmem_get_cache()
+ * while belonging to a cgroup, and later on changes. This is considered
+ * acceptable, and should only happen upon task migration.
+ *
+ * Before the cache is created by the memcg core, there is also a possible
+ * imbalance: the task belongs to a memcg, but the cache being allocated from
+ * is the global cache, since the child cache is not yet guaranteed to be
+ * ready. This case is also fine, since in this case the GFP_KMEMCG will not be
+ * passed and the page allocator will not attempt any cgroup accounting.
+ */
+static __always_inline struct kmem_cache *
+memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp)
+{
+ if (!memcg_kmem_enabled())
+ return cachep;
+ if (gfp & __GFP_NOFAIL)
+ return cachep;
+ if (in_interrupt() || (!current->mm) || (current->flags & PF_KTHREAD))
+ return cachep;
+
+ return __memcg_kmem_get_cache(cachep, gfp);
+}
#endif /* _LINUX_MEMCONTROL_H */

diff --git a/init/Kconfig b/init/Kconfig
index 707d015..31c4f74 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -741,7 +741,7 @@ config MEMCG_SWAP_ENABLED
then swapaccount=0 does the trick).
config MEMCG_KMEM
bool "Memory Resource Controller Kernel Memory accounting (EXPERIMENTAL)"
- depends on MEMCG && EXPERIMENTAL
+ depends on MEMCG && EXPERIMENTAL && !SLOB
default n
help
The Kernel Memory extension for Memory Resource Controller can limit
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 04851bb..1cce5c3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -339,6 +339,11 @@ struct mem_cgroup {
#ifdef CONFIG_INET
struct tcp_memcontrol tcp_mem;
#endif
+
+#ifdef CONFIG_MEMCG_KMEM
+ /* Slab accounting */
+ struct kmem_cache *slabs[MAX_KMEM_CACHE_TYPES];
+#endif
};

enum {
@@ -539,6 +544,40 @@ static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
(memcg->kmem_accounted & (KMEM_ACCOUNTED_MASK));
}

+static char *memcg_cache_name(struct mem_cgroup *memcg, struct kmem_cache *cachep)
+{
+ char *name;
+ struct dentry *dentry;
+
+ rcu_read_lock();
+ dentry = rcu_dereference(memcg->css.cgroup->dentry);
+ rcu_read_unlock();
+
+ BUG_ON(dentry == NULL);
+
+ name = kasprintf(GFP_KERNEL, "%s(%d:%s)",
+ cachep->name, css_id(&memcg->css), dentry->d_name.name);
+
+ return name;
+}
+
+static struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
+ struct kmem_cache *s)
+{
+ char *name;
+ struct kmem_cache *new;
+
+ name = memcg_cache_name(memcg, s);
+ if (!name)
+ return NULL;
+
+ new = kmem_cache_create_memcg(memcg, name, s->object_size, s->align,
+ (s->flags & ~SLAB_PANIC), s->ctor);
+
+ kfree(name);
+ return new;
+}
+
struct ida cache_types;

void __init memcg_init_kmem_cache(void)
@@ -665,6 +704,170 @@ static void disarm_kmem_keys(struct mem_cgroup *memcg)
*/
WARN_ON(res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0);
}
+
+static DEFINE_MUTEX(memcg_cache_mutex);
+static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
+ struct kmem_cache *cachep)
+{
+ struct kmem_cache *new_cachep;
+ int idx;
+
+ BUG_ON(!memcg_can_account_kmem(memcg));
+
+ idx = cachep->memcg_params.id;
+
+ mutex_lock(&memcg_cache_mutex);
+ new_cachep = memcg->slabs[idx];
+ if (new_cachep)
+ goto out;
+
+ new_cachep = kmem_cache_dup(memcg, cachep);
+
+ if (new_cachep == NULL) {
+ new_cachep = cachep;
+ goto out;
+ }
+
+ mem_cgroup_get(memcg);
+ memcg->slabs[idx] = new_cachep;
+ new_cachep->memcg_params.memcg = memcg;
+out:
+ mutex_unlock(&memcg_cache_mutex);
+ return new_cachep;
+}
+
+struct create_work {
+ struct mem_cgroup *memcg;
+ struct kmem_cache *cachep;
+ struct list_head list;
+};
+
+/* Use a single spinlock for destruction and creation, not a frequent op */
+static DEFINE_SPINLOCK(cache_queue_lock);
+static LIST_HEAD(create_queue);
+
+/*
+ * Flush the queue of kmem_caches to create, because we're creating a cgroup.
+ *
+ * We might end up flushing other cgroups' creation requests as well, but
+ * they will just get queued again next time someone tries to make a slab
+ * allocation for them.
+ */
+void memcg_flush_cache_create_queue(void)
+{
+ struct create_work *cw, *tmp;
+ unsigned long flags;
+
+ spin_lock_irqsave(&cache_queue_lock, flags);
+ list_for_each_entry_safe(cw, tmp, &create_queue, list) {
+ list_del(&cw->list);
+ kfree(cw);
+ }
+ spin_unlock_irqrestore(&cache_queue_lock, flags);
+}
+
+static void memcg_create_cache_work_func(struct work_struct *w)
+{
+ struct create_work *cw, *tmp;
+ unsigned long flags;
+ LIST_HEAD(create_unlocked);
+
+ spin_lock_irqsave(&cache_queue_lock, flags);
+ list_for_each_entry_safe(cw, tmp, &create_queue, list)
+ list_move(&cw->list, &create_unlocked);
+ spin_unlock_irqrestore(&cache_queue_lock, flags);
+
+ list_for_each_entry_safe(cw, tmp, &create_unlocked, list) {
+ list_del(&cw->list);
+ memcg_create_kmem_cache(cw->memcg, cw->cachep);
+ /* Drop the reference gotten when we enqueued. */
+ css_put(&cw->memcg->css);
+ kfree(cw);
+ }
+}
+
+static DECLARE_WORK(memcg_create_cache_work, memcg_create_cache_work_func);
+
+/*
+ * Enqueue the creation of a per-memcg kmem_cache.
+ * Called with rcu_read_lock.
+ */
+static void memcg_create_cache_enqueue(struct mem_cgroup *memcg,
+ struct kmem_cache *cachep)
+{
+ struct create_work *cw;
+ unsigned long flags;
+
+ spin_lock_irqsave(&cache_queue_lock, flags);
+ list_for_each_entry(cw, &create_queue, list) {
+ if (cw->memcg == memcg && cw->cachep == cachep) {
+ spin_unlock_irqrestore(&cache_queue_lock, flags);
+ return;
+ }
+ }
+ spin_unlock_irqrestore(&cache_queue_lock, flags);
+
+ /* The corresponding put will be done in the workqueue. */
+ if (!css_tryget(&memcg->css))
+ return;
+
+ cw = kmalloc(sizeof(struct create_work), GFP_NOWAIT);
+ if (cw == NULL) {
+ css_put(&memcg->css);
+ return;
+ }
+
+ cw->memcg = memcg;
+ cw->cachep = cachep;
+ spin_lock_irqsave(&cache_queue_lock, flags);
+ list_add_tail(&cw->list, &create_queue);
+ spin_unlock_irqrestore(&cache_queue_lock, flags);
+
+ schedule_work(&memcg_create_cache_work);
+}
+
+/*
+ * Return the kmem_cache we're supposed to use for a slab allocation.
+ * We try to use the current memcg's version of the cache.
+ *
+ * If the cache does not exist yet, if we are the first user of it,
+ * we either create it immediately, if possible, or create it asynchronously
+ * in a workqueue.
+ * In the latter case, we will let the current allocation go through with
+ * the original cache.
+ *
+ * Can't be called in interrupt context or from kernel threads.
+ * This function needs to be called with rcu_read_lock() held.
+ */
+struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep,
+ gfp_t gfp)
+{
+ struct mem_cgroup *memcg;
+ int idx;
+ struct task_struct *p;
+
+ if (cachep->memcg_params.memcg)
+ return cachep;
+
+ idx = cachep->memcg_params.id;
+ VM_BUG_ON(idx == -1);
+
+ rcu_read_lock();
+ p = rcu_dereference(current->mm->owner);
+ memcg = mem_cgroup_from_task(p);
+ rcu_read_unlock();
+
+ if (!memcg_can_account_kmem(memcg))
+ return cachep;
+
+ if (memcg->slabs[idx] == NULL) {
+ memcg_create_cache_enqueue(memcg, cachep);
+ return cachep;
+ }
+
+ return memcg->slabs[idx];
+}
+EXPORT_SYMBOL(__memcg_kmem_get_cache);
#else
static void disarm_kmem_keys(struct mem_cgroup *memcg)
{
--
1.7.11.4


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