2 files changed, 147 insertions, 6 deletions

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index b871f2552b45..e726fb0df719 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -262,10 +262,12 @@ some of the pages cached in the cgroup (page cache pages).
 4.2 Task migration
 
 When a task migrates from one cgroup to another, it's charge is not
-carried forward. The pages allocated from the original cgroup still
+carried forward by default. The pages allocated from the original cgroup still
 remain charged to it, the charge is dropped when the page is freed or
 reclaimed.
 
+Note: You can move charges of a task along with task migration. See 8.
+
 4.3 Removing a cgroup
 
 A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a
@@ -414,7 +416,57 @@ NOTE1: Soft limits take effect over a long period of time, since they involve
 NOTE2: It is recommended to set the soft limit always below the hard limit,
        otherwise the hard limit will take precedence.
 
-8. TODO
+8. Move charges at task migration
+
+Users can move charges associated with a task along with task migration, that
+is, uncharge task's pages from the old cgroup and charge them to the new cgroup.
+
+8.1 Interface
+
+This feature is disabled by default. It can be enabled(and disabled again) by
+writing to memory.move_charge_at_immigrate of the destination cgroup.
+
+If you want to enable it:
+
+# echo (some positive value) > memory.move_charge_at_immigrate
+
+Note: Each bits of move_charge_at_immigrate has its own meaning about what type
+      of charges should be moved. See 8.2 for details.
+Note: Charges are moved only when you move mm->owner, IOW, a leader of a thread
+      group.
+Note: If we cannot find enough space for the task in the destination cgroup, we
+      try to make space by reclaiming memory. Task migration may fail if we
+      cannot make enough space.
+Note: It can take several seconds if you move charges in giga bytes order.
+
+And if you want disable it again:
+
+# echo 0 > memory.move_charge_at_immigrate
+
+8.2 Type of charges which can be move
+
+Each bits of move_charge_at_immigrate has its own meaning about what type of
+charges should be moved.
+
+  bit | what type of charges would be moved ?
+ -----+------------------------------------------------------------------------
+   0  | A charge of an anonymous page(or swap of it) used by the target task.
+      | Those pages and swaps must be used only by the target task. You must
+      | enable Swap Extension(see 2.4) to enable move of swap charges.
+
+Note: Those pages and swaps must be charged to the old cgroup.
+Note: More type of pages(e.g. file cache, shmem,) will be supported by other
+      bits in future.
+
+8.3 TODO
+
+- Add support for other types of pages(e.g. file cache, shmem, etc.).
+- Implement madvise(2) to let users decide the vma to be moved or not to be
+  moved.
+- All of moving charge operations are done under cgroup_mutex. It's not good
+  behavior to hold the mutex too long, so we may need some trick.
+
+9. 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 d813823ab08f..59ffaf511d77 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -226,11 +226,26 @@ struct mem_cgroup {
         bool            memsw_is_minimum;
 
         /*
+         * Should we move charges of a task when a task is moved into this
+         * mem_cgroup ? And what type of charges should we move ?
+         */
+        unsigned long   move_charge_at_immigrate;
+
+        /*
          * statistics. This must be placed at the end of memcg.
          */
         struct mem_cgroup_stat stat;
 };
 
+/* Stuffs for move charges at task migration. */
+/*
+ * Types of charges to be moved. "move_charge_at_immitgrate" is treated as a
+ * left-shifted bitmap of these types.
+ */
+enum move_type {
+        NR_MOVE_TYPE,
+};
+
 /*
  * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
  * limit reclaim to prevent infinite loops, if they ever occur.
@@ -2865,6 +2880,31 @@ static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
         return 0;
 }
 
+static u64 mem_cgroup_move_charge_read(struct cgroup *cgrp,
+                                        struct cftype *cft)
+{
+        return mem_cgroup_from_cont(cgrp)->move_charge_at_immigrate;
+}
+
+static int mem_cgroup_move_charge_write(struct cgroup *cgrp,
+                                        struct cftype *cft, u64 val)
+{
+        struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);
+
+        if (val >= (1 << NR_MOVE_TYPE))
+                return -EINVAL;
+        /*
+         * We check this value several times in both in can_attach() and
+         * attach(), so we need cgroup lock to prevent this value from being
+         * inconsistent.
+         */
+        cgroup_lock();
+        mem->move_charge_at_immigrate = val;
+        cgroup_unlock();
+
+        return 0;
+}
+
 
 /* For read statistics */
 enum {
@@ -3098,6 +3138,11 @@ static struct cftype mem_cgroup_files[] = {
                 .read_u64 = mem_cgroup_swappiness_read,
                 .write_u64 = mem_cgroup_swappiness_write,
         },
+        {
+                .name = "move_charge_at_immigrate",
+                .read_u64 = mem_cgroup_move_charge_read,
+                .write_u64 = mem_cgroup_move_charge_write,
+        },
 };
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
@@ -3345,6 +3390,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
         if (parent)
                 mem->swappiness = get_swappiness(parent);
         atomic_set(&mem->refcnt, 1);
+        mem->move_charge_at_immigrate = 0;
         return &mem->css;
 free_out:
         __mem_cgroup_free(mem);
@@ -3381,16 +3427,57 @@ static int mem_cgroup_populate(struct cgroup_subsys *ss,
         return ret;
 }
 
+/* Handlers for move charge at task migration. */
+static int mem_cgroup_can_move_charge(void)
+{
+        return 0;
+}
+
+static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
+                                struct cgroup *cgroup,
+                                struct task_struct *p,
+                                bool threadgroup)
+{
+        int ret = 0;
+        struct mem_cgroup *mem = mem_cgroup_from_cont(cgroup);
+
+        if (mem->move_charge_at_immigrate) {
+                struct mm_struct *mm;
+                struct mem_cgroup *from = mem_cgroup_from_task(p);
+
+                VM_BUG_ON(from == mem);
+
+                mm = get_task_mm(p);
+                if (!mm)
+                        return 0;
+
+                /* We move charges only when we move a owner of the mm */
+                if (mm->owner == p)
+                        ret = mem_cgroup_can_move_charge();
+
+                mmput(mm);
+        }
+        return ret;
+}
+
+static void mem_cgroup_cancel_attach(struct cgroup_subsys *ss,
+                                struct cgroup *cgroup,
+                                struct task_struct *p,
+                                bool threadgroup)
+{
+}
+
+static void mem_cgroup_move_charge(void)
+{
+}
+
 static void mem_cgroup_move_task(struct cgroup_subsys *ss,
                                 struct cgroup *cont,
                                 struct cgroup *old_cont,
                                 struct task_struct *p,
                                 bool threadgroup)
 {
-        /*
-         * FIXME: It's better to move charges of this process from old
-         * memcg to new memcg. But it's just on TODO-List now.
-         */
+        mem_cgroup_move_charge();
 }
 
 struct cgroup_subsys mem_cgroup_subsys = {
@@ -3400,6 +3487,8 @@ struct cgroup_subsys mem_cgroup_subsys = {
         .pre_destroy = mem_cgroup_pre_destroy,
         .destroy = mem_cgroup_destroy,
         .populate = mem_cgroup_populate,
+        .can_attach = mem_cgroup_can_attach,
+        .cancel_attach = mem_cgroup_cancel_attach,
         .attach = mem_cgroup_move_task,
         .early_init = 0,
         .use_id = 1,