mm: memcontrol: fold mem_cgroup_start_move()/mem_cgroup_end_move()

	return memcg->swappiness;

}

/*

 * memcg->moving_account is used for checking possibility that some thread is

 * calling move_account(). When a thread on CPU-A starts moving pages under

 * a memcg, other threads should check memcg->moving_account under

 * rcu_read_lock(), like this:

 *

 *         CPU-A                                    CPU-B

 *                                              rcu_read_lock()

 *         memcg->moving_account+1              if (memcg->mocing_account)

 *                                                   take heavy locks.

 *         synchronize_rcu()                    update something.

 *                                              rcu_read_unlock()

 *         start move here.

 */

static void mem_cgroup_start_move(struct mem_cgroup *memcg)

{

	atomic_inc(&memcg->moving_account);

	synchronize_rcu();

}

static void mem_cgroup_end_move(struct mem_cgroup *memcg)

{

	atomic_dec(&memcg->moving_account);

}

/*

 * A routine for checking "mem" is under move_account() or not.

 *

	mc.from = NULL;

	mc.to = NULL;

	spin_unlock(&mc.lock);

	mem_cgroup_end_move(from);

	atomic_dec(&from->moving_account);

}

static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,

			VM_BUG_ON(mc.precharge);

			VM_BUG_ON(mc.moved_charge);

			VM_BUG_ON(mc.moved_swap);

			mem_cgroup_start_move(from);

			/*

			 * Signal mem_cgroup_begin_page_stat() to take

			 * the memcg's move_lock while we're moving

			 * its pages to another memcg.  Then wait for

			 * already started RCU-only updates to finish.

			 */

			atomic_inc(&from->moving_account);

			synchronize_rcu();

			spin_lock(&mc.lock);

			mc.from = from;

			mc.to = memcg;