[PATCH 2/2] mm/cgroup: delay soft limit data allocation

[Laurent Dufour]

Until a soft limit is set to a cgroup, the soft limit data are useless
so delay this allocation when a limit is set.

Suggested-by: Michal Hocko <mho...@kernel.org>
Signed-off-by: Laurent Dufour <lduf...@linux.vnet.ibm.com>
---
 mm/memcontrol.c | 52 +++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 39 insertions(+), 13 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 228ac44f77e1..bc2e6ab69c0c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -142,6 +142,8 @@ struct mem_cgroup_tree {
        struct mem_cgroup_tree_per_node *rb_tree_per_node[MAX_NUMNODES];
 };
 
+static DEFINE_MUTEX(soft_limit_mutex);
+static bool soft_limit_initialized;
 static struct mem_cgroup_tree soft_limit_tree __read_mostly;
 
 /* for OOM */
@@ -381,6 +383,36 @@ mem_cgroup_page_nodeinfo(struct mem_cgroup *memcg, struct 
page *page)
        return memcg->nodeinfo[nid];
 }
 
+static void soft_limit_initialize(void)
+{
+       int node;
+
+       mutex_lock(&soft_limit_mutex);
+       if (soft_limit_initialized)
+               goto bail;
+
+       for_each_node(node) {
+               struct mem_cgroup_tree_per_node *rtpn;
+
+               rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL,
+                                   node_online(node) ? node : NUMA_NO_NODE);
+               /* Best effort, but should we warn if allocation failed */
+               if (rtpn) {
+                       rtpn->rb_root = RB_ROOT;
+                       spin_lock_init(&rtpn->lock);
+                       /*
+                        * We don't want the compiler to set rb_tree_per_node
+                        * before rb_root and lock are initialized.
+                        */
+                       WRITE_ONCE(soft_limit_tree.rb_tree_per_node[node],
+                                  rtpn);
+               }
+       }
+       soft_limit_initialized = true;
+bail:
+       mutex_unlock(&soft_limit_mutex);
+}
+
 static struct mem_cgroup_tree_per_node *
 soft_limit_tree_node(int nid)
 {
@@ -465,6 +497,8 @@ static void mem_cgroup_update_tree(struct mem_cgroup 
*memcg, struct page *page)
        struct mem_cgroup_tree_per_node *mctz;
 
        mctz = soft_limit_tree_from_page(page);
+       if (!mctz)
+               return;
        /*
         * Necessary to update all ancestors when hierarchy is used.
         * because their event counter is not touched.
@@ -502,7 +536,8 @@ static void mem_cgroup_remove_from_trees(struct mem_cgroup 
*memcg)
        for_each_node(nid) {
                mz = mem_cgroup_nodeinfo(memcg, nid);
                mctz = soft_limit_tree_node(nid);
-               mem_cgroup_remove_exceeded(mz, mctz);
+               if (mctz)
+                       mem_cgroup_remove_exceeded(mz, mctz);
        }
 }
 
@@ -3000,6 +3035,8 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file 
*of,
                }
                break;
        case RES_SOFT_LIMIT:
+               if (!soft_limit_initialized)
+                       soft_limit_initialize();
                memcg->soft_limit = nr_pages;
                ret = 0;
                break;
@@ -5774,7 +5811,7 @@ __setup("cgroup.memory=", cgroup_memory);
  */
 static int __init mem_cgroup_init(void)
 {
-       int cpu, node;
+       int cpu;
 
 #ifndef CONFIG_SLOB
        /*
@@ -5794,17 +5831,6 @@ static int __init mem_cgroup_init(void)
                INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work,
                          drain_local_stock);
 
-       for_each_node(node) {
-               struct mem_cgroup_tree_per_node *rtpn;
-
-               rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL,
-                                   node_online(node) ? node : NUMA_NO_NODE);
-
-               rtpn->rb_root = RB_ROOT;
-               spin_lock_init(&rtpn->lock);
-               soft_limit_tree.rb_tree_per_node[node] = rtpn;
-       }
-
        return 0;
 }
 subsys_initcall(mem_cgroup_init);
-- 
2.7.4