Kamezawa Hiroyuki [off-list ref] writes:

(2012/06/09 18:00), Aneesh Kumar K.V wrote:

quoted

From: "Aneesh Kumar K.V"<redacted>

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<redacted>

one comment.

quoted

---
  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;

Why do you need  cgroup_exclude/release rmdir here ? you holds hugetlb_lock()
and charges will not be empty, here.

 But even without empty charge, we can still remove the cgroup right ?
 ie if we don't have any task but some charge in the cgroup because of
 shared mmap in hugetlbfs. 

-aneesh

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