cpuset: replace cpuset->stack_list with cpuset_for_each_descendant_pre()

Implement cpuset_for_each_descendant_pre() and replace the
cpuset-specific tree walking using cpuset->stack_list with it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Li Zefan <lizefan@huawei.com>

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 5e348ae37ce9b4903cb5bb4bff144861f0d1b8d4..0ddb48d40e4da56b50a086a246c60d47acd68886 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -103,9 +103,6 @@ struct cpuset {
        /* for custom sched domain */
        int relax_domain_level;
 
-       /* used for walking a cpuset hierarchy */
-       struct list_head stack_list;
-
        struct work_struct hotplug_work;
 };
 
@@ -207,6 +204,20 @@ static struct cpuset top_cpuset = {
        cgroup_for_each_child((pos_cgrp), (parent_cs)->css.cgroup)      \
                if (is_cpuset_online(((child_cs) = cgroup_cs((pos_cgrp)))))
 
+/**
+ * cpuset_for_each_descendant_pre - pre-order walk of a cpuset's descendants
+ * @des_cs: loop cursor pointing to the current descendant
+ * @pos_cgrp: used for iteration
+ * @root_cs: target cpuset to walk ancestor of
+ *
+ * Walk @des_cs through the online descendants of @root_cs.  Must be used
+ * with RCU read locked.  The caller may modify @pos_cgrp by calling
+ * cgroup_rightmost_descendant() to skip subtree.
+ */
+#define cpuset_for_each_descendant_pre(des_cs, pos_cgrp, root_cs)      \
+       cgroup_for_each_descendant_pre((pos_cgrp), (root_cs)->css.cgroup) \
+               if (is_cpuset_online(((des_cs) = cgroup_cs((pos_cgrp)))))
+
 /*
  * There are two global mutexes guarding cpuset structures - cpuset_mutex
  * and callback_mutex.  The latter may nest inside the former.  We also
@@ -507,31 +518,24 @@ update_domain_attr(struct sched_domain_attr *dattr, struct cpuset *c)
        return;
 }
 
-static void
-update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
+static void update_domain_attr_tree(struct sched_domain_attr *dattr,
+                                   struct cpuset *root_cs)
 {
-       LIST_HEAD(q);
-
-       list_add(&c->stack_list, &q);
-       while (!list_empty(&q)) {
-               struct cpuset *cp;
-               struct cgroup *cont;
-               struct cpuset *child;
-
-               cp = list_first_entry(&q, struct cpuset, stack_list);
-               list_del(q.next);
+       struct cpuset *cp;
+       struct cgroup *pos_cgrp;
 
-               if (cpumask_empty(cp->cpus_allowed))
+       rcu_read_lock();
+       cpuset_for_each_descendant_pre(cp, pos_cgrp, root_cs) {
+               /* skip the whole subtree if @cp doesn't have any CPU */
+               if (cpumask_empty(cp->cpus_allowed)) {
+                       pos_cgrp = cgroup_rightmost_descendant(pos_cgrp);
                        continue;
+               }
 
                if (is_sched_load_balance(cp))
                        update_domain_attr(dattr, cp);
-
-               rcu_read_lock();
-               cpuset_for_each_child(child, cont, cp)
-                       list_add_tail(&child->stack_list, &q);
-               rcu_read_unlock();
        }
+       rcu_read_unlock();
 }
 
 /*
@@ -591,7 +595,6 @@ update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
 static int generate_sched_domains(cpumask_var_t **domains,
                        struct sched_domain_attr **attributes)
 {
-       LIST_HEAD(q);           /* queue of cpusets to be scanned */
        struct cpuset *cp;      /* scans q */
        struct cpuset **csa;    /* array of all cpuset ptrs */
        int csn;                /* how many cpuset ptrs in csa so far */
@@ -600,6 +603,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
        struct sched_domain_attr *dattr;  /* attributes for custom domains */
        int ndoms = 0;          /* number of sched domains in result */
        int nslot;              /* next empty doms[] struct cpumask slot */
+       struct cgroup *pos_cgrp;
 
        doms = NULL;
        dattr = NULL;
@@ -627,33 +631,27 @@ static int generate_sched_domains(cpumask_var_t **domains,
                goto done;
        csn = 0;
 
-       list_add(&top_cpuset.stack_list, &q);
-       while (!list_empty(&q)) {
-               struct cgroup *cont;
-               struct cpuset *child;   /* scans child cpusets of cp */
-
-               cp = list_first_entry(&q, struct cpuset, stack_list);
-               list_del(q.next);
-
-               if (cpumask_empty(cp->cpus_allowed))
-                       continue;
-
+       rcu_read_lock();
+       cpuset_for_each_descendant_pre(cp, pos_cgrp, &top_cpuset) {
                /*
-                * All child cpusets contain a subset of the parent's cpus, so
-                * just skip them, and then we call update_domain_attr_tree()
-                * to calc relax_domain_level of the corresponding sched
-                * domain.
+                * Continue traversing beyond @cp iff @cp has some CPUs and
+                * isn't load balancing.  The former is obvious.  The
+                * latter: All child cpusets contain a subset of the
+                * parent's cpus, so just skip them, and then we call
+                * update_domain_attr_tree() to calc relax_domain_level of
+                * the corresponding sched domain.
                 */
-               if (is_sched_load_balance(cp)) {
-                       csa[csn++] = cp;
+               if (!cpumask_empty(cp->cpus_allowed) &&
+                   !is_sched_load_balance(cp))
                        continue;
-               }
 
-               rcu_read_lock();
-               cpuset_for_each_child(child, cont, cp)
-                       list_add_tail(&child->stack_list, &q);
-               rcu_read_unlock();
-       }
+               if (is_sched_load_balance(cp))
+                       csa[csn++] = cp;
+
+               /* skip @cp's subtree */
+               pos_cgrp = cgroup_rightmost_descendant(pos_cgrp);
+       }
+       rcu_read_unlock();
 
        for (i = 0; i < csn; i++)
                csa[i]->pn = i;
@@ -2068,31 +2066,6 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
        move_member_tasks_to_cpuset(cs, parent);
 }
 
-/*
- * Helper function to traverse cpusets.
- * It can be used to walk the cpuset tree from top to bottom, completing
- * one layer before dropping down to the next (thus always processing a
- * node before any of its children).
- */
-static struct cpuset *cpuset_next(struct list_head *queue)
-{
-       struct cpuset *cp;
-       struct cpuset *child;   /* scans child cpusets of cp */
-       struct cgroup *cont;
-
-       if (list_empty(queue))
-               return NULL;
-
-       cp = list_first_entry(queue, struct cpuset, stack_list);
-       list_del(queue->next);
-       rcu_read_lock();
-       cpuset_for_each_child(child, cont, cp)
-               list_add_tail(&child->stack_list, queue);
-       rcu_read_unlock();
-
-       return cp;
-}
-
 /**
  * cpuset_propagate_hotplug_workfn - propagate CPU/memory hotplug to a cpuset
  * @cs: cpuset in interest
@@ -2229,12 +2202,12 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
        /* if cpus or mems went down, we need to propagate to descendants */
        if (cpus_offlined || mems_offlined) {
                struct cpuset *cs;
-               LIST_HEAD(queue);
+               struct cgroup *pos_cgrp;
 
-               list_add_tail(&top_cpuset.stack_list, &queue);
-               while ((cs = cpuset_next(&queue)))
-                       if (cs != &top_cpuset)
-                               schedule_cpuset_propagate_hotplug(cs);
+               rcu_read_lock();
+               cpuset_for_each_descendant_pre(cs, pos_cgrp, &top_cpuset)
+                       schedule_cpuset_propagate_hotplug(cs);
+               rcu_read_unlock();
        }
 
        mutex_unlock(&cpuset_mutex);