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

Having these functions and their documentation split out and somewhere makes it harder, not easier, to follow what's going on. Inline them directly where charge moving is prepared and finished, and put an explanation right next to it. Signed-off-by: Johannes Weiner <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Vladimir Davydov <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
chewitt · Dec 11, 2014 · 247b144 · 247b144
1 parent 4e2f245
commit 247b144
Showing 1 changed file with 12 additions and 28 deletions.
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
@@ -1446,32 +1446,6 @@ int mem_cgroup_swappiness(struct mem_cgroup *memcg)
 	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.
  *
@@ -5431,7 +5405,8 @@ static void mem_cgroup_clear_mc(void)
 	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,
@@ -5464,7 +5439,16 @@ 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;