memcg: export struct mem_cgroup

mem_cgroup structure is defined in mm/memcontrol.c currently which means
that the code outside of this file has to use external API even for
trivial access stuff.

This patch exports mm_struct with its dependencies and makes some of the
exported functions inlines.  This even helps to reduce the code size a bit
(make defconfig + CONFIG_MEMCG=y)

  text		data    bss     dec     	 hex 	filename
  12355346        1823792 1089536 15268674         e8fb42 vmlinux.before
  12354970        1823792 1089536 15268298         e8f9ca vmlinux.after

This is not much (370B) but better than nothing.

We also save a function call in some hot paths like callers of
mem_cgroup_count_vm_event which is used for accounting.

The patch doesn't introduce any functional changes.

[vdavykov@parallels.com: inline memcg_kmem_is_active]
[vdavykov@parallels.com: do not expose type outside of CONFIG_MEMCG]
[akpm@linux-foundation.org: memcontrol.h needs eventfd.h for eventfd_ctx]
[akpm@linux-foundation.org: export mem_cgroup_from_task() to modules]
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/swap.h

@@ -351,7 +351,15 @@ extern void check_move_unevictable_pages(struct page **, int nr_pages);
 extern int kswapd_run(int nid);
 extern void kswapd_stop(int nid);
 #ifdef CONFIG_MEMCG
-extern int mem_cgroup_swappiness(struct mem_cgroup *mem);
+static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
+{
+	/* root ? */
+	if (mem_cgroup_disabled() || !memcg->css.parent)
+		return vm_swappiness;
+
+	return memcg->swappiness;
+}
+
 #else
 static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
 {

include/net/sock.h

@@ -1042,34 +1042,6 @@ struct proto {
 #endif
 };
 
-/*
- * Bits in struct cg_proto.flags
- */
-enum cg_proto_flags {
-	/* Currently active and new sockets should be assigned to cgroups */
-	MEMCG_SOCK_ACTIVE,
-	/* It was ever activated; we must disarm static keys on destruction */
-	MEMCG_SOCK_ACTIVATED,
-};
-
-struct cg_proto {
-	struct page_counter	memory_allocated;	/* Current allocated memory. */
-	struct percpu_counter	sockets_allocated;	/* Current number of sockets. */
-	int			memory_pressure;
-	long			sysctl_mem[3];
-	unsigned long		flags;
-	/*
-	 * memcg field is used to find which memcg we belong directly
-	 * Each memcg struct can hold more than one cg_proto, so container_of
-	 * won't really cut.
-	 *
-	 * The elegant solution would be having an inverse function to
-	 * proto_cgroup in struct proto, but that means polluting the structure
-	 * for everybody, instead of just for memcg users.
-	 */
-	struct mem_cgroup	*memcg;
-};
-
 int proto_register(struct proto *prot, int alloc_slab);
 void proto_unregister(struct proto *prot);
 

mm/memory-failure.c

@@ -146,7 +146,7 @@ static int hwpoison_filter_task(struct page *p)
 	if (!mem)
 		return -EINVAL;
 
-	css = mem_cgroup_css(mem);
+	css = &mem->css;
 	ino = cgroup_ino(css->cgroup);
 	css_put(css);
 

mm/slab_common.c

@@ -500,7 +500,7 @@ 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 */
-	struct cgroup_subsys_state *css = mem_cgroup_css(memcg);
+	struct cgroup_subsys_state *css = &memcg->css;
 	struct memcg_cache_array *arr;
 	struct kmem_cache *s = NULL;
 	char *cache_name;

mm/vmscan.c

@@ -175,7 +175,7 @@ static bool sane_reclaim(struct scan_control *sc)
 	if (!memcg)
 		return true;
 #ifdef CONFIG_CGROUP_WRITEBACK
-	if (cgroup_on_dfl(mem_cgroup_css(memcg)->cgroup))
+	if (memcg->css.cgroup)
 		return true;
 #endif
 	return false;