Memory controller: task migration

Allow tasks to migrate from one cgroup to the other.  We migrate
mm_struct's mem_cgroup only when the thread group id migrates.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: David Rientjes <rientjes@google.com>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ebca767292dc..b25df2a9d024 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -326,11 +326,46 @@ static int mem_cgroup_populate(struct cgroup_subsys *ss,
                                         ARRAY_SIZE(mem_cgroup_files));
 }
 
+static void mem_cgroup_move_task(struct cgroup_subsys *ss,
+                                struct cgroup *cont,
+                                struct cgroup *old_cont,
+                                struct task_struct *p)
+{
+        struct mm_struct *mm;
+        struct mem_cgroup *mem, *old_mem;
+
+        mm = get_task_mm(p);
+        if (mm == NULL)
+                return;
+
+        mem = mem_cgroup_from_cont(cont);
+        old_mem = mem_cgroup_from_cont(old_cont);
+
+        if (mem == old_mem)
+                goto out;
+
+        /*
+         * Only thread group leaders are allowed to migrate, the mm_struct is
+         * in effect owned by the leader
+         */
+        if (p->tgid != p->pid)
+                goto out;
+
+        css_get(&mem->css);
+        rcu_assign_pointer(mm->mem_cgroup, mem);
+        css_put(&old_mem->css);
+
+out:
+        mmput(mm);
+        return;
+}
+
 struct cgroup_subsys mem_cgroup_subsys = {
         .name = "memory",
         .subsys_id = mem_cgroup_subsys_id,
         .create = mem_cgroup_create,
         .destroy = mem_cgroup_destroy,
         .populate = mem_cgroup_populate,
+        .attach = mem_cgroup_move_task,
         .early_init = 1,
 };