hugetlb/cgroup: add support for cgroup removal

Add support for cgroup removal.  If we don't have parent cgroup, the
charges are moved to root cgroup.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hillf Danton <dhillf@gmail.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 68 insertions, 2 deletions

diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index 63e04cfa437d..bc518bedea98 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -105,10 +105,76 @@ static void hugetlb_cgroup_destroy(struct cgroup *cgroup)
         kfree(h_cgroup);
 }
 
+
+/*
+ * Should be called with hugetlb_lock held.
+ * Since we are holding hugetlb_lock, pages cannot get moved from
+ * active list or uncharged from the cgroup, So no need to get
+ * page reference and test for page active here. This function
+ * cannot fail.
+ */
+static void hugetlb_cgroup_move_parent(int idx, struct cgroup *cgroup,
+                                       struct page *page)
+{
+        int csize;
+        struct res_counter *counter;
+        struct res_counter *fail_res;
+        struct hugetlb_cgroup *page_hcg;
+        struct hugetlb_cgroup *h_cg   = hugetlb_cgroup_from_cgroup(cgroup);
+        struct hugetlb_cgroup *parent = parent_hugetlb_cgroup(cgroup);
+
+        page_hcg = hugetlb_cgroup_from_page(page);
+        /*
+         * We can have pages in active list without any cgroup
+         * ie, hugepage with less than 3 pages. We can safely
+         * ignore those pages.
+         */
+        if (!page_hcg || page_hcg != h_cg)
+                goto out;
+
+        csize = PAGE_SIZE << compound_order(page);
+        if (!parent) {
+                parent = root_h_cgroup;
+                /* root has no limit */
+                res_counter_charge_nofail(&parent->hugepage[idx],
+                                          csize, &fail_res);
+        }
+        counter = &h_cg->hugepage[idx];
+        res_counter_uncharge_until(counter, counter->parent, csize);
+
+        set_hugetlb_cgroup(page, parent);
+out:
+        return;
+}
+
+/*
+ * Force the hugetlb cgroup to empty the hugetlb resources by moving them to
+ * the parent cgroup.
+ */
 static int hugetlb_cgroup_pre_destroy(struct cgroup *cgroup)
 {
-        /* We will add the cgroup removal support in later patches */
-           return -EBUSY;
+        struct hstate *h;
+        struct page *page;
+        int ret = 0, idx = 0;
+
+        do {
+                if (cgroup_task_count(cgroup) ||
+                    !list_empty(&cgroup->children)) {
+                        ret = -EBUSY;
+                        goto out;
+                }
+                for_each_hstate(h) {
+                        spin_lock(&hugetlb_lock);
+                        list_for_each_entry(page, &h->hugepage_activelist, lru)
+                                hugetlb_cgroup_move_parent(idx, cgroup, page);
+
+                        spin_unlock(&hugetlb_lock);
+                        idx++;
+                }
+                cond_resched();
+        } while (hugetlb_cgroup_have_usage(cgroup));
+out:
+        return ret;
 }
 
 int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,