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Date: Wed, 5 Jun 2013 17:16:59 +0800
From: Li Zefan <lizefan@...wei.com>
To: Tejun Heo <tj@...nel.org>
CC: LKML <linux-kernel@...r.kernel.org>,
Cgroups <cgroups@...r.kernel.org>,
Containers <containers@...ts.linux-foundation.org>
Subject: [PATCH v2 08/10] cpuset: allow to keep tasks in empty cpusets
To achieve this:
- We call update_tasks_cpumask/nodemask() for empty cpusets when
hotplug happens, instead of moving tasks out of them.
- When a cpuset's masks are changed by writing cpuset.cpus/mems,
we also update tasks in child cpusets which are empty.
v2:
- drop rcu_read_lock before calling update_task_nodemask() and
update_task_cpumask(), instead of using workqueue.
- add documentation in include/linux/cgroup.h
Signed-off-by: Li Zefan <lizefan@...wei.com>
---
include/linux/cgroup.h | 4 ++
kernel/cpuset.c | 137 +++++++++++++++++++++++++++++++++++++++++--------
2 files changed, 120 insertions(+), 21 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index d0ad379..53e81a6 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -277,6 +277,10 @@ enum {
*
* - Remount is disallowed.
*
+ * - cpuset: tasks will be kept in empty cpusets when hotplug happens
+ * and take masks of ancestors with non-empty cpus/mems, instead of
+ * being moved to an ancestor.
+ *
* - memcg: use_hierarchy is on by default and the cgroup file for
* the flag is not created.
*
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 5252f94..3b93098 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -878,6 +878,49 @@ static void update_tasks_cpumask(struct cpuset *cs, struct ptr_heap *heap)
cgroup_scan_tasks(&scan);
}
+/*
+ * update_tasks_cpumask_hier - Update the cpumasks of tasks in the hierarchy.
+ * @root_cs: the root cpuset of the hierarchy
+ * @update_root: update root cpuset or not?
+ * @heap: the heap used by cgroup_scan_tasks()
+ *
+ * This will update cpumasks of tasks in @root_cs and all other empty cpusets
+ * which take on cpumask of @root_cs.
+ *
+ * Called with cpuset_mutex held
+ */
+static void update_tasks_cpumask_hier(struct cpuset *root_cs,
+ bool update_root, struct ptr_heap *heap)
+{
+ struct cpuset *cp;
+ struct cgroup *pos_cgrp;
+
+ if (update_root)
+ update_tasks_cpumask(root_cs, heap);
+
+ rcu_read_lock();
+ cpuset_for_each_descendant_pre(cp, pos_cgrp, root_cs) {
+ /* skip the whole subtree if @cp have some CPU */
+ if (!cpumask_empty(cp->cpus_allowed)) {
+ pos_cgrp = cgroup_rightmost_descendant(pos_cgrp);
+ continue;
+ }
+ if (!css_tryget(&cp->css))
+ continue;
+ rcu_read_unlock();
+
+ update_tasks_cpumask(cp, heap);
+
+ rcu_read_lock();
+ /*
+ * We should acquire rcu_read_lock first, so it's still
+ * valid to access @cp after dropping the css refcnt.
+ */
+ css_put(&cp->css);
+ }
+ rcu_read_unlock();
+}
+
/**
* update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
* @cs: the cpuset to consider
@@ -929,11 +972,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
mutex_unlock(&callback_mutex);
- /*
- * Scan tasks in the cpuset, and update the cpumasks of any
- * that need an update.
- */
- update_tasks_cpumask(cs, &heap);
+ update_tasks_cpumask_hier(cs, true, &heap);
heap_free(&heap);
@@ -1101,6 +1140,49 @@ static void update_tasks_nodemask(struct cpuset *cs, struct ptr_heap *heap)
}
/*
+ * update_tasks_nodemask_hier - Update the nodemasks of tasks in the hierarchy.
+ * @cs: the root cpuset of the hierarchy
+ * @update_root: update the root cpuset or not?
+ * @heap: the heap used by cgroup_scan_tasks()
+ *
+ * This will update nodemasks of tasks in @root_cs and all other empty cpusets
+ * which take on nodemask of @root_cs.
+ *
+ * Called with cpuset_mutex held
+ */
+static void update_tasks_nodemask_hier(struct cpuset *root_cs,
+ bool update_root, struct ptr_heap *heap)
+{
+ struct cpuset *cp;
+ struct cgroup *pos_cgrp;
+
+ if (update_root)
+ update_tasks_nodemask(root_cs, heap);
+
+ rcu_read_lock();
+ cpuset_for_each_descendant_pre(cp, pos_cgrp, root_cs) {
+ /* skip the whole subtree if @cp have some CPU */
+ if (!nodes_empty(cp->mems_allowed)) {
+ pos_cgrp = cgroup_rightmost_descendant(pos_cgrp);
+ continue;
+ }
+ if (!css_tryget(&cp->css))
+ continue;
+ rcu_read_unlock();
+
+ update_tasks_nodemask(cp, heap);
+
+ rcu_read_lock();
+ /*
+ * We should acquire rcu_read_lock first, so it's still
+ * valid to access @cp after dropping the css refcnt.
+ */
+ css_put(&cp->css);
+ }
+ rcu_read_unlock();
+}
+
+/*
* Handle user request to change the 'mems' memory placement
* of a cpuset. Needs to validate the request, update the
* cpusets mems_allowed, and for each task in the cpuset,
@@ -1164,7 +1246,7 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
cs->mems_allowed = trialcs->mems_allowed;
mutex_unlock(&callback_mutex);
- update_tasks_nodemask(cs, &heap);
+ update_tasks_nodemask_hier(cs, true, &heap);
heap_free(&heap);
done:
@@ -2064,27 +2146,36 @@ static void cpuset_propagate_hotplug_workfn(struct work_struct *work)
static nodemask_t off_mems;
struct cpuset *cs = container_of(work, struct cpuset, hotplug_work);
bool is_empty;
+ bool sane = cgroup_sane_behavior(cs->css.cgroup);
mutex_lock(&cpuset_mutex);
cpumask_andnot(&off_cpus, cs->cpus_allowed, top_cpuset.cpus_allowed);
nodes_andnot(off_mems, cs->mems_allowed, top_cpuset.mems_allowed);
- /* remove offline cpus from @cs */
- if (!cpumask_empty(&off_cpus)) {
- mutex_lock(&callback_mutex);
- cpumask_andnot(cs->cpus_allowed, cs->cpus_allowed, &off_cpus);
- mutex_unlock(&callback_mutex);
+ mutex_lock(&callback_mutex);
+ cpumask_andnot(cs->cpus_allowed, cs->cpus_allowed, &off_cpus);
+ mutex_unlock(&callback_mutex);
+
+ /*
+ * If sane_behavior flag is set, we need to update tasks' cpumask
+ * for empty cpuset to take on ancestor's cpumask
+ */
+ if ((sane && cpumask_empty(cs->cpus_allowed)) ||
+ !cpumask_empty(&off_cpus))
update_tasks_cpumask(cs, NULL);
- }
- /* remove offline mems from @cs */
- if (!nodes_empty(off_mems)) {
- mutex_lock(&callback_mutex);
- nodes_andnot(cs->mems_allowed, cs->mems_allowed, off_mems);
- mutex_unlock(&callback_mutex);
+ mutex_lock(&callback_mutex);
+ nodes_andnot(cs->mems_allowed, cs->mems_allowed, off_mems);
+ mutex_unlock(&callback_mutex);
+
+ /*
+ * If sane_behavior flag is set, we need to update tasks' nodemask
+ * for empty cpuset to take on ancestor's nodemask
+ */
+ if ((sane && nodes_empty(cs->mems_allowed)) ||
+ !nodes_empty(off_mems))
update_tasks_nodemask(cs, NULL);
- }
is_empty = cpumask_empty(cs->cpus_allowed) ||
nodes_empty(cs->mems_allowed);
@@ -2092,11 +2183,13 @@ static void cpuset_propagate_hotplug_workfn(struct work_struct *work)
mutex_unlock(&cpuset_mutex);
/*
- * If @cs became empty, move tasks to the nearest ancestor with
- * execution resources. This is full cgroup operation which will
+ * If sane_behavior flag is set, we'll keep tasks in empty cpusets.
+ *
+ * Otherwise move tasks to the nearest ancestor with execution
+ * resources. This is full cgroup operation which will
* also call back into cpuset. Should be done outside any lock.
*/
- if (is_empty)
+ if (!sane && is_empty)
remove_tasks_in_empty_cpuset(cs);
/* the following may free @cs, should be the last operation */
@@ -2171,6 +2264,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
mutex_unlock(&callback_mutex);
/* we don't mess with cpumasks of tasks in top_cpuset */
+ update_tasks_cpumask_hier(&top_cpuset, false, NULL);
}
/* synchronize mems_allowed to N_MEMORY */
@@ -2179,6 +2273,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
top_cpuset.mems_allowed = new_mems;
mutex_unlock(&callback_mutex);
update_tasks_nodemask(&top_cpuset, NULL);
+ update_tasks_nodemask_hier(&top_cpuset, false, NULL);
}
/* if cpus or mems went down, we need to propagate to descendants */
--
1.8.0.2
--
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