[PATCH 13/23] slub: create duplicate cache

[Glauber Costa]

This patch provides kmem_cache_dup(), that duplicates
a cache for a memcg, preserving its creation properties.
Object size, alignment and flags are all respected.

When a duplicate cache is created, the parent cache cannot
be destructed during the child lifetime. To assure this,
its reference count is increased if the cache creation
succeeds.

Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
CC: Christoph Lameter <cl@xxxxxxxxx>
CC: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
CC: Michal Hocko <mhocko@xxxxxxx>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
CC: Johannes Weiner <hannes@xxxxxxxxxxx>
CC: Suleiman Souhlal <suleiman@xxxxxxxxxx>
---
 include/linux/memcontrol.h |    3 +++
 include/linux/slab.h       |    3 +++
 mm/memcontrol.c            |   44 ++++++++++++++++++++++++++++++++++++++++++++
 mm/slub.c                  |   37 +++++++++++++++++++++++++++++++++++++
 4 files changed, 87 insertions(+), 0 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 99e14b9..493ecdd 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -445,6 +445,9 @@ int memcg_css_id(struct mem_cgroup *memcg);
 void mem_cgroup_register_cache(struct mem_cgroup *memcg,
 				      struct kmem_cache *s);
 void mem_cgroup_release_cache(struct kmem_cache *cachep);
+extern char *mem_cgroup_cache_name(struct mem_cgroup *memcg,
+				   struct kmem_cache *cachep);
+
 #else
 static inline void mem_cgroup_register_cache(struct mem_cgroup *memcg,
 					     struct kmem_cache *s)
diff --git a/include/linux/slab.h b/include/linux/slab.h
index c7a7e05..909b508 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -323,6 +323,9 @@ extern void *__kmalloc_track_caller(size_t, gfp_t, unsigned long);
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
 #define MAX_KMEM_CACHE_TYPES 400
+extern struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
+					 struct kmem_cache *cachep);
+void kmem_cache_drop_ref(struct kmem_cache *cachep);
 #else
 #define MAX_KMEM_CACHE_TYPES 0
 #endif /* CONFIG_CGROUP_MEM_RES_CTLR_KMEM */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0015ed0..e881d83 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -467,6 +467,50 @@ struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg)
 EXPORT_SYMBOL(tcp_proto_cgroup);
 #endif /* CONFIG_INET */
 
+/*
+ * This is to prevent races againt the kmalloc cache creations.
+ * Should never be used outside the core memcg code. Therefore,
+ * copy it here, instead of letting it in lib/
+ */
+static char *kasprintf_no_account(gfp_t gfp, const char *fmt, ...)
+{
+	unsigned int len;
+	char *p = NULL;
+	va_list ap, aq;
+
+	va_start(ap, fmt);
+	va_copy(aq, ap);
+	len = vsnprintf(NULL, 0, fmt, aq);
+	va_end(aq);
+
+	p = kmalloc_no_account(len+1, gfp);
+	if (!p)
+		goto out;
+
+	vsnprintf(p, len+1, fmt, ap);
+
+out:
+	va_end(ap);
+	return p;
+}
+
+char *mem_cgroup_cache_name(struct mem_cgroup *memcg, struct kmem_cache *cachep)
+{
+	char *name;
+	struct dentry *dentry = memcg->css.cgroup->dentry;
+
+	BUG_ON(dentry == NULL);
+
+	/* Preallocate the space for "dead" at the end */
+	name = kasprintf_no_account(GFP_KERNEL, "%s(%d:%s)dead",
+	    cachep->name, css_id(&memcg->css), dentry->d_name.name);
+
+	if (name)
+		/* Remove "dead" */
+		name[strlen(name) - 4] = '\0';
+	return name;
+}
+
 /* Bitmap used for allocating the cache id numbers. */
 static DECLARE_BITMAP(cache_types, MAX_KMEM_CACHE_TYPES);
 
diff --git a/mm/slub.c b/mm/slub.c
index 86e40cc..2285a96 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3993,6 +3993,43 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 }
 EXPORT_SYMBOL(kmem_cache_create);
 
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
+				  struct kmem_cache *s)
+{
+	char *name;
+	struct kmem_cache *new;
+
+	name = mem_cgroup_cache_name(memcg, s);
+	if (!name)
+		return NULL;
+
+	new = kmem_cache_create_memcg(memcg, name, s->objsize, s->align,
+				      s->allocflags, s->ctor);
+
+	/*
+	 * We increase the reference counter in the parent cache, to
+	 * prevent it from being deleted. If kmem_cache_destroy() is
+	 * called for the root cache before we call it for a child cache,
+	 * it will be queued for destruction when we finally drop the
+	 * reference on the child cache.
+	 */
+	if (new) {
+		down_write(&slub_lock);
+		s->refcount++;
+		up_write(&slub_lock);
+	}
+
+	return new;
+}
+
+void kmem_cache_drop_ref(struct kmem_cache *s)
+{
+	BUG_ON(s->memcg_params.id != -1);
+	kmem_cache_destroy(s);
+}
+#endif
+
 #ifdef CONFIG_SMP
 /*
  * Use the cpu notifier to insure that the cpu slabs are flushed when
-- 
1.7.7.6

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