cgroup: rename ->create/post_create/pre_destroy/destroy() to ->css_alloc/online/offline/free()

Rename cgroup_subsys css lifetime related callbacks to better describe
what their roles are.  Also, update documentation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index 0d3a1a3..b5bde7a 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -77,7 +77,7 @@
 	return false;
 }
 
-static struct cgroup_subsys_state *hugetlb_cgroup_create(struct cgroup *cgroup)
+static struct cgroup_subsys_state *hugetlb_cgroup_css_alloc(struct cgroup *cgroup)
 {
 	int idx;
 	struct cgroup *parent_cgroup;
@@ -101,7 +101,7 @@
 	return &h_cgroup->css;
 }
 
-static void hugetlb_cgroup_destroy(struct cgroup *cgroup)
+static void hugetlb_cgroup_css_free(struct cgroup *cgroup)
 {
 	struct hugetlb_cgroup *h_cgroup;
 
@@ -155,7 +155,7 @@
  * Force the hugetlb cgroup to empty the hugetlb resources by moving them to
  * the parent cgroup.
  */
-static void hugetlb_cgroup_pre_destroy(struct cgroup *cgroup)
+static void hugetlb_cgroup_css_offline(struct cgroup *cgroup)
 {
 	struct hstate *h;
 	struct page *page;
@@ -404,8 +404,8 @@
 
 struct cgroup_subsys hugetlb_subsys = {
 	.name = "hugetlb",
-	.create     = hugetlb_cgroup_create,
-	.pre_destroy = hugetlb_cgroup_pre_destroy,
-	.destroy    = hugetlb_cgroup_destroy,
-	.subsys_id  = hugetlb_subsys_id,
+	.css_alloc	= hugetlb_cgroup_css_alloc,
+	.css_offline	= hugetlb_cgroup_css_offline,
+	.css_free	= hugetlb_cgroup_css_free,
+	.subsys_id	= hugetlb_subsys_id,
 };