2 files changed, 57 insertions, 11 deletions

diff --git a/Documentation/controllers/memory.txt b/Documentation/controllers/memory.txt
index 58f32c166fac..54253b7a8db2 100644
--- a/Documentation/controllers/memory.txt
+++ b/Documentation/controllers/memory.txt
@@ -237,11 +237,30 @@ reclaimed.
 A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a
 cgroup might have some charge associated with it, even though all
 tasks have migrated away from it.
-Such charges are moved to its parent as much as possible and freed if parent
-is full. Both of RSS and CACHES are moved to parent.
-If both of them are busy, rmdir() returns -EBUSY.
+Such charges are freed(at default) or moved to its parent. When moved,
+both of RSS and CACHES are moved to parent.
+If both of them are busy, rmdir() returns -EBUSY. See 5.1 Also.
 
-5. TODO
+5. Misc. interfaces.
+
+5.1 force_empty
+  memory.force_empty interface is provided to make cgroup's memory usage empty.
+  You can use this interface only when the cgroup has no tasks.
+  When writing anything to this
+
+  # echo 0 > memory.force_empty
+
+  Almost all pages tracked by this memcg will be unmapped and freed. Some of
+  pages cannot be freed because it's locked or in-use. Such pages are moved
+  to parent and this cgroup will be empty. But this may return -EBUSY in
+  some too busy case.
+
+  Typical use case of this interface is that calling this before rmdir().
+  Because rmdir() moves all pages to parent, some out-of-use page caches can be
+  moved to the parent. If you want to avoid that, force_empty will be useful.
+
+
+6. TODO
 
 1. Add support for accounting huge pages (as a separate controller)
 2. Make per-cgroup scanner reclaim not-shared pages first
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e00f25e6545f..decace3bb57e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1062,21 +1062,27 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *mem,
  * make mem_cgroup's charge to be 0 if there is no task.
  * This enables deleting this mem_cgroup.
  */
-static int mem_cgroup_force_empty(struct mem_cgroup *mem)
+static int mem_cgroup_force_empty(struct mem_cgroup *mem, bool free_all)
 {
         int ret;
         int node, zid, shrink;
         int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+        struct cgroup *cgrp = mem->css.cgroup;
 
         css_get(&mem->css);
 
         shrink = 0;
+        /* should free all ? */
+        if (free_all)
+                goto try_to_free;
 move_account:
         while (mem->res.usage > 0) {
                 ret = -EBUSY;
-                if (atomic_read(&mem->css.cgroup->count) > 0)
+                if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
+                        goto out;
+                ret = -EINTR;
+                if (signal_pending(current))
                         goto out;
-
                 /* This is for making all *used* pages to be on LRU. */
                 lru_add_drain_all();
                 ret = 0;
@@ -1106,19 +1112,29 @@ out:
         return ret;
 
 try_to_free:
-        /* returns EBUSY if we come here twice. */
-        if (shrink)  {
+        /* returns EBUSY if there is a task or if we come here twice. */
+        if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children) || shrink) {
                 ret = -EBUSY;
                 goto out;
         }
+        /* we call try-to-free pages for make this cgroup empty */
+        lru_add_drain_all();
         /* try to free all pages in this cgroup */
         shrink = 1;
         while (nr_retries && mem->res.usage > 0) {
                 int progress;
+
+                if (signal_pending(current)) {
+                        ret = -EINTR;
+                        goto out;
+                }
                 progress = try_to_free_mem_cgroup_pages(mem,
                                                   GFP_HIGHUSER_MOVABLE);
-                if (!progress)
+                if (!progress) {
                         nr_retries--;
+                        /* maybe some writeback is necessary */
+                        congestion_wait(WRITE, HZ/10);
+                }
 
         }
         /* try move_account...there may be some *locked* pages. */
@@ -1128,6 +1144,12 @@ try_to_free:
         goto out;
 }
 
+int mem_cgroup_force_empty_write(struct cgroup *cont, unsigned int event)
+{
+        return mem_cgroup_force_empty(mem_cgroup_from_cont(cont), true);
+}
+
+
 static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
 {
         return res_counter_read_u64(&mem_cgroup_from_cont(cont)->res,
@@ -1225,6 +1247,7 @@ static int mem_control_stat_show(struct cgroup *cont, struct cftype *cft,
         return 0;
 }
 
+
 static struct cftype mem_cgroup_files[] = {
         {
                 .name = "usage_in_bytes",
@@ -1253,6 +1276,10 @@ static struct cftype mem_cgroup_files[] = {
                 .name = "stat",
                 .read_map = mem_control_stat_show,
         },
+        {
+                .name = "force_empty",
+                .trigger = mem_cgroup_force_empty_write,
+        },
 };
 
 static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
@@ -1350,7 +1377,7 @@ static void mem_cgroup_pre_destroy(struct cgroup_subsys *ss,
                                         struct cgroup *cont)
 {
         struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
-        mem_cgroup_force_empty(mem);
+        mem_cgroup_force_empty(mem, false);
 }
 
 static void mem_cgroup_destroy(struct cgroup_subsys *ss,