hotplug cpu move tasks in empty cpusets - refinements

- Narrow the scope of callback_mutex in scan_for_empty_cpusets().

- Avoid rewriting the cpus, mems of cpusets except when it is likely that
  we'll be changing them.

- Have remove_tasks_in_empty_cpuset() also check for empty mems.

Signed-off-by: Paul Jackson <pj@sgi.com>
Acked-by: Cliff Wickman <cpw@sgi.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 8 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 6868c1e78917..67b2bfe27814 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1709,7 +1709,8 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
          * has online cpus, so can't be empty).
          */
         parent = cs->parent;
-        while (cpus_empty(parent->cpus_allowed))
+        while (cpus_empty(parent->cpus_allowed) ||
+                        nodes_empty(parent->mems_allowed))
                 parent = parent->parent;
 
         move_member_tasks_to_cpuset(cs, parent);
@@ -1741,7 +1742,6 @@ static void scan_for_empty_cpusets(const struct cpuset *root)
 
         list_add_tail((struct list_head *)&root->stack_list, &queue);
 
-        mutex_lock(&callback_mutex);
         while (!list_empty(&queue)) {
                 cp = container_of(queue.next, struct cpuset, stack_list);
                 list_del(queue.next);
@@ -1750,19 +1750,24 @@ static void scan_for_empty_cpusets(const struct cpuset *root)
                         list_add_tail(&child->stack_list, &queue);
                 }
                 cont = cp->css.cgroup;
+
+                /* Continue past cpusets with all cpus, mems online */
+                if (cpus_subset(cp->cpus_allowed, cpu_online_map) &&
+                    nodes_subset(cp->mems_allowed, node_states[N_HIGH_MEMORY]))
+                        continue;
+
                 /* Remove offline cpus and mems from this cpuset. */
+                mutex_lock(&callback_mutex);
                 cpus_and(cp->cpus_allowed, cp->cpus_allowed, cpu_online_map);
                 nodes_and(cp->mems_allowed, cp->mems_allowed,
                                                 node_states[N_HIGH_MEMORY]);
+                mutex_unlock(&callback_mutex);
+
+                /* Move tasks from the empty cpuset to a parent */
                 if (cpus_empty(cp->cpus_allowed) ||
-                     nodes_empty(cp->mems_allowed)) {
-                        /* Move tasks from the empty cpuset to a parent */
-                        mutex_unlock(&callback_mutex);
+                     nodes_empty(cp->mems_allowed))
                         remove_tasks_in_empty_cpuset(cp);
-                        mutex_lock(&callback_mutex);
-                }
         }
-        mutex_unlock(&callback_mutex);
 }
 
 /*