cpusets: restructure the function cpuset_update_task_memory_state()

The kernel still allocates the page caches on old node after modifying its
cpuset's mems when 'memory_spread_page' was set, or it didn't spread the
page cache evenly over all the nodes that faulting task is allowed to usr
after memory_spread_page was set.  it is caused by the old mem_allowed and
flags of the task, the current kernel doesn't updates them unless some
function invokes cpuset_update_task_memory_state(), it is too late
sometimes.We must update the mem_allowed and the flags of the tasks in
time.

Slab has the same problem.

The following patches fix this bug by updating tasks' mem_allowed and
spread flag after its cpuset's mems or spread flag is changed.

This patch:

Extract a function from cpuset_update_task_memory_state().  It will be
used later for update tasks' page/slab spread flags after its cpuset's
flag is set
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Paul Menage <menage@google.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Yasunori Goto <y-goto@jp.fujitsu.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/cpuset.c

@@ -331,6 +331,24 @@ static void guarantee_online_mems(const struct cpuset *cs, nodemask_t *pmask)
 	BUG_ON(!nodes_intersects(*pmask, node_states[N_HIGH_MEMORY]));
 }
 
+/*
+ * update task's spread flag if cpuset's page/slab spread flag is set
+ *
+ * Called with callback_mutex/cgroup_mutex held
+ */
+static void cpuset_update_task_spread_flag(struct cpuset *cs,
+					struct task_struct *tsk)
+{
+	if (is_spread_page(cs))
+		tsk->flags |= PF_SPREAD_PAGE;
+	else
+		tsk->flags &= ~PF_SPREAD_PAGE;
+	if (is_spread_slab(cs))
+		tsk->flags |= PF_SPREAD_SLAB;
+	else
+		tsk->flags &= ~PF_SPREAD_SLAB;
+}
+
 /**
  * cpuset_update_task_memory_state - update task memory placement
  *
@@ -388,14 +406,7 @@ void cpuset_update_task_memory_state(void)
 		cs = task_cs(tsk); /* Maybe changed when task not locked */
 		guarantee_online_mems(cs, &tsk->mems_allowed);
 		tsk->cpuset_mems_generation = cs->mems_generation;
-		if (is_spread_page(cs))
-			tsk->flags |= PF_SPREAD_PAGE;
-		else
-			tsk->flags &= ~PF_SPREAD_PAGE;
-		if (is_spread_slab(cs))
-			tsk->flags |= PF_SPREAD_SLAB;
-		else
-			tsk->flags &= ~PF_SPREAD_SLAB;
+		cpuset_update_task_spread_flag(cs, tsk);
 		task_unlock(tsk);
 		mutex_unlock(&callback_mutex);
 		mpol_rebind_task(tsk, &tsk->mems_allowed);