we can be sure that old page won't get uncharged till the last
put_page().

Signed-off-by: Aneesh Kumar K.V <redacted>
---
 include/linux/hugetlb_cgroup.h |    8 ++++++++
 mm/hugetlb_cgroup.c            |   21 +++++++++++++++++++++
 mm/migrate.c                   |    5 +++++
 3 files changed, 34 insertions(+)

diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
index ba4836f..b64d067 100644
--- a/include/linux/hugetlb_cgroup.h
+++ b/include/linux/hugetlb_cgroup.h

@@ -63,6 +63,8 @@ extern void hugetlb_cgroup_uncharge_page(int idx, unsigned long nr_pages,
 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)
 {

@@ -112,5 +114,11 @@ 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 */
 #endif

diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index c2b7b8e..2d384fe 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c

@@ -394,6 +394,27 @@ int __init hugetlb_cgroup_file_init(int idx)
 	return 0;
 }
 
+void hugetlb_cgroup_migrate(struct page *oldhpage, struct page *newhpage)
+{
+	struct hugetlb_cgroup *h_cg;
+
+	VM_BUG_ON(!PageHuge(oldhpage));
+
+	if (hugetlb_cgroup_disabled())
+		return;
+
+	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,

diff --git a/mm/migrate.c b/mm/migrate.c
index fdce3a2..6c37c51 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c

@@ -33,6 +33,7 @@
 #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>

@@ -931,6 +932,10 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 
 	if (anon_vma)
 		put_anon_vma(anon_vma);
+
+	if (!rc)
+		hugetlb_cgroup_migrate(hpage, new_hpage);
+
 	unlock_page(hpage);
 out:
 	put_page(new_hpage);

-- 
1.7.10