hugetlb/cgroup: migrate hugetlb cgroup info from oldpage to new page during migration

With HugeTLB pages, hugetlb cgroup is uncharged in compound page
destructor. Since we are holding a hugepage reference, we can be sure
that old page won't get uncharged till the last put_page().

Signed-off-by: Aneesh Kumar K.V <[e-mail]>
Cc: David Rientjes <[e-mail]>
Acked-by: KAMEZAWA Hiroyuki <[e-mail]>
Cc: Hillf Danton <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: KOSAKI Motohiro <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/hugetlb_cgroup.h

···
 extern void hugetlb_cgroup_uncharge_cgroup(int idx, unsigned long nr_pages,
 					   struct hugetlb_cgroup *h_cg);
 extern int hugetlb_cgroup_file_init(int idx) __init;
+extern void hugetlb_cgroup_migrate(struct page *oldhpage,
+				   struct page *newhpage);
 
 #else
 static inline struct hugetlb_cgroup *hugetlb_cgroup_from_page(struct page *page)
···
 static inline int __init hugetlb_cgroup_file_init(int idx)
 {
 	return 0;
+}
+
+static inline void hugetlb_cgroup_migrate(struct page *oldhpage,
+					  struct page *newhpage)
+{
+	return;
 }
 
 #endif  /* CONFIG_MEM_RES_CTLR_HUGETLB */

mm/hugetlb_cgroup.c

···
 	return 0;
 }
 
+void hugetlb_cgroup_migrate(struct page *oldhpage, struct page *newhpage)
+{
+	struct hugetlb_cgroup *h_cg;
+
+	if (hugetlb_cgroup_disabled())
+		return;
+
+	VM_BUG_ON(!PageHuge(oldhpage));
+	spin_lock(&hugetlb_lock);
+	h_cg = hugetlb_cgroup_from_page(oldhpage);
+	set_hugetlb_cgroup(oldhpage, NULL);
+	cgroup_exclude_rmdir(&h_cg->css);
+
+	/* move the h_cg details to new cgroup */
+	set_hugetlb_cgroup(newhpage, h_cg);
+	spin_unlock(&hugetlb_lock);
+	cgroup_release_and_wakeup_rmdir(&h_cg->css);
+	return;
+}
+
 struct cgroup_subsys hugetlb_subsys = {
 	.name = "hugetlb",
 	.create     = hugetlb_cgroup_create,

mm/migrate.c

···
 #include <linux/memcontrol.h>
 #include <linux/syscalls.h>
 #include <linux/hugetlb.h>
+#include <linux/hugetlb_cgroup.h>
 #include <linux/gfp.h>
 
 #include <asm/tlbflush.h>
···
 
 	if (anon_vma)
 		put_anon_vma(anon_vma);
+
+	if (!rc)
+		hugetlb_cgroup_migrate(hpage, new_hpage);
+
 	unlock_page(hpage);
 out:
 	put_page(new_hpage);