* Any task can increment and decrement the count field without lock.
* So in general, code holding cgroup_mutex can't rely on the count
* field not changing. However, if the count goes to zero, then only
- * attach_task() can increment it again. Because a count of zero
+ * cgroup_attach_task() can increment it again. Because a count of zero
* means that no tasks are currently attached, therefore there is no
* way a task attached to that cgroup can fork (the other way to
* increment the count). So code holding cgroup_mutex can safely
* The task_lock() exception
*
* The need for this exception arises from the action of
- * attach_task(), which overwrites one tasks cgroup pointer with
+ * cgroup_attach_task(), which overwrites one tasks cgroup pointer with
* another. It does so using cgroup_mutexe, however there are
* several performance critical places that need to reference
* task->cgroup without the expense of grabbing a system global
* mutex. Therefore except as noted below, when dereferencing or, as
- * in attach_task(), modifying a task'ss cgroup pointer we use
+ * in cgroup_attach_task(), modifying a task'ss cgroup pointer we use
* task_lock(), which acts on a spinlock (task->alloc_lock) already in
* the task_struct routinely used for such matters.
*
* P.S. One more locking exception. RCU is used to guard the
- * update of a tasks cgroup pointer by attach_task()
+ * update of a tasks cgroup pointer by cgroup_attach_task()
*/
/**
* Call holding cgroup_mutex. May take task_lock of
* the task 'pid' during call.
*/
-static int attach_task(struct cgroup *cgrp, struct task_struct *tsk)
+int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
int retval = 0;
struct cgroup_subsys *ss;
get_task_struct(tsk);
}
- ret = attach_task(cgrp, tsk);
+ ret = cgroup_attach_task(cgrp, tsk);
put_task_struct(tsk);
return ret;
}
* - Used for /proc/<pid>/cgroup.
* - No need to task_lock(tsk) on this tsk->cgroup reference, as it
* doesn't really matter if tsk->cgroup changes after we read it,
- * and we take cgroup_mutex, keeping attach_task() from changing it
+ * and we take cgroup_mutex, keeping cgroup_attach_task() from changing it
* anyway. No need to check that tsk->cgroup != NULL, thanks to
* the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
* cgroup to top_cgroup.
* A pointer to the shared css_set was automatically copied in
* fork.c by dup_task_struct(). However, we ignore that copy, since
* it was not made under the protection of RCU or cgroup_mutex, so
- * might no longer be a valid cgroup pointer. attach_task() might
+ * might no longer be a valid cgroup pointer. cgroup_attach_task() might
* have already changed current->cgroups, allowing the previously
* referenced cgroup group to be removed and freed.
*
* attach us to a different cgroup, decrementing the count on
* the first cgroup that we never incremented. But in this case,
* top_cgroup isn't going away, and either task has PF_EXITING set,
- * which wards off any attach_task() attempts, or task is a failed
- * fork, never visible to attach_task.
+ * which wards off any cgroup_attach_task() attempts, or task is a failed
+ * fork, never visible to cgroup_attach_task.
*
*/
void cgroup_exit(struct task_struct *tsk, int run_callbacks)
}
/* All seems fine. Finish by moving the task into the new cgroup */
- ret = attach_task(child, tsk);
+ ret = cgroup_attach_task(child, tsk);
mutex_unlock(&cgroup_mutex);
out_release:
#include <asm/atomic.h>
#include <linux/mutex.h>
#include <linux/kfifo.h>
+#include <linux/workqueue.h>
+#include <linux/cgroup.h>
/*
* Tracks how many cpusets are currently defined in system.
/* partition number for rebuild_sched_domains() */
int pn;
+
+ /* used for walking a cpuset heirarchy */
+ struct list_head stack_list;
};
/* Retrieve the cpuset for a cgroup */
return container_of(task_subsys_state(task, cpuset_subsys_id),
struct cpuset, css);
}
-
+struct cpuset_hotplug_scanner {
+ struct cgroup_scanner scan;
+ struct cgroup *to;
+};
/* bits in struct cpuset flags field */
typedef enum {
return 0;
}
+/**
+ * cpuset_do_move_task - move a given task to another cpuset
+ * @tsk: pointer to task_struct the task to move
+ * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner
+ *
+ * Called by cgroup_scan_tasks() for each task in a cgroup.
+ * Return nonzero to stop the walk through the tasks.
+ */
+void cpuset_do_move_task(struct task_struct *tsk, struct cgroup_scanner *scan)
+{
+ struct cpuset_hotplug_scanner *chsp;
+
+ chsp = container_of(scan, struct cpuset_hotplug_scanner, scan);
+ cgroup_attach_task(chsp->to, tsk);
+}
+
+/**
+ * move_member_tasks_to_cpuset - move tasks from one cpuset to another
+ * @from: cpuset in which the tasks currently reside
+ * @to: cpuset to which the tasks will be moved
+ *
+ * Called with manage_sem held
+ * callback_mutex must not be held, as attach_task() will take it.
+ *
+ * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
+ * calling callback functions for each.
+ */
+static void move_member_tasks_to_cpuset(struct cpuset *from, struct cpuset *to)
+{
+ struct cpuset_hotplug_scanner scan;
+
+ scan.scan.cg = from->css.cgroup;
+ scan.scan.test_task = NULL; /* select all tasks in cgroup */
+ scan.scan.process_task = cpuset_do_move_task;
+ scan.scan.heap = NULL;
+ scan.to = to->css.cgroup;
+
+ if (cgroup_scan_tasks((struct cgroup_scanner *)&scan))
+ printk(KERN_ERR "move_member_tasks_to_cpuset: "
+ "cgroup_scan_tasks failed\n");
+}
+
/*
* If common_cpu_mem_hotplug_unplug(), below, unplugs any CPUs
* or memory nodes, we need to walk over the cpuset hierarchy,
* removing that CPU or node from all cpusets. If this removes the
- * last CPU or node from a cpuset, then the guarantee_online_cpus()
- * or guarantee_online_mems() code will use that emptied cpusets
- * parent online CPUs or nodes. Cpusets that were already empty of
- * CPUs or nodes are left empty.
- *
- * This routine is intentionally inefficient in a couple of regards.
- * It will check all cpusets in a subtree even if the top cpuset of
- * the subtree has no offline CPUs or nodes. It checks both CPUs and
- * nodes, even though the caller could have been coded to know that
- * only one of CPUs or nodes needed to be checked on a given call.
- * This was done to minimize text size rather than cpu cycles.
+ * last CPU or node from a cpuset, then move the tasks in the empty
+ * cpuset to its next-highest non-empty parent.
*
- * Call with both manage_mutex and callback_mutex held.
+ * The parent cpuset has some superset of the 'mems' nodes that the
+ * newly empty cpuset held, so no migration of memory is necessary.
*
- * Recursive, on depth of cpuset subtree.
+ * Called with both manage_sem and callback_sem held
*/
+static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
+{
+ struct cpuset *parent;
+
+ /* the cgroup's css_sets list is in use if there are tasks
+ in the cpuset; the list is empty if there are none;
+ the cs->css.refcnt seems always 0 */
+ if (list_empty(&cs->css.cgroup->css_sets))
+ return;
-static void guarantee_online_cpus_mems_in_subtree(const struct cpuset *cur)
+ /*
+ * Find its next-highest non-empty parent, (top cpuset
+ * has online cpus, so can't be empty).
+ */
+ parent = cs->parent;
+ while (cpus_empty(parent->cpus_allowed)) {
+ /*
+ * this empty cpuset should now be considered to
+ * have been used, and therefore eligible for
+ * release when empty (if it is notify_on_release)
+ */
+ parent = parent->parent;
+ }
+
+ move_member_tasks_to_cpuset(cs, parent);
+}
+
+/*
+ * Walk the specified cpuset subtree and look for empty cpusets.
+ * The tasks of such cpuset must be moved to a parent cpuset.
+ *
+ * Note that such a notify_on_release cpuset must have had, at some time,
+ * member tasks or cpuset descendants and cpus and memory, before it can
+ * be a candidate for release.
+ *
+ * Called with manage_mutex held. We take callback_mutex to modify
+ * cpus_allowed and mems_allowed.
+ *
+ * This walk processes the tree from top to bottom, completing one layer
+ * before dropping down to the next. It always processes a node before
+ * any of its children.
+ *
+ * For now, since we lack memory hot unplug, we'll never see a cpuset
+ * that has tasks along with an empty 'mems'. But if we did see such
+ * a cpuset, we'd handle it just like we do if its 'cpus' was empty.
+ */
+static void scan_for_empty_cpusets(const struct cpuset *root)
{
+ struct cpuset *cp; /* scans cpusets being updated */
+ struct cpuset *child; /* scans child cpusets of cp */
+ struct list_head queue;
struct cgroup *cont;
- struct cpuset *c;
- /* Each of our child cpusets mems must be online */
- list_for_each_entry(cont, &cur->css.cgroup->children, sibling) {
- c = cgroup_cs(cont);
- guarantee_online_cpus_mems_in_subtree(c);
- if (!cpus_empty(c->cpus_allowed))
- guarantee_online_cpus(c, &c->cpus_allowed);
- if (!nodes_empty(c->mems_allowed))
- guarantee_online_mems(c, &c->mems_allowed);
+ INIT_LIST_HEAD(&queue);
+
+ 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);
+ list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
+ child = cgroup_cs(cont);
+ list_add_tail(&child->stack_list, &queue);
+ }
+ cont = cp->css.cgroup;
+ /* Remove offline cpus and mems from this cpuset. */
+ cpus_and(cp->cpus_allowed, cp->cpus_allowed, cpu_online_map);
+ nodes_and(cp->mems_allowed, cp->mems_allowed,
+ node_states[N_HIGH_MEMORY]);
+ if ((cpus_empty(cp->cpus_allowed) ||
+ nodes_empty(cp->mems_allowed))) {
+ /* Move tasks from the empty cpuset to a parent */
+ mutex_unlock(&callback_mutex);
+ remove_tasks_in_empty_cpuset(cp);
+ mutex_lock(&callback_mutex);
+ }
}
+ mutex_unlock(&callback_mutex);
+ return;
}
/*
* The cpus_allowed and mems_allowed nodemasks in the top_cpuset track
* cpu_online_map and node_states[N_HIGH_MEMORY]. Force the top cpuset to
- * track what's online after any CPU or memory node hotplug or unplug
- * event.
- *
- * To ensure that we don't remove a CPU or node from the top cpuset
- * that is currently in use by a child cpuset (which would violate
- * the rule that cpusets must be subsets of their parent), we first
- * call the recursive routine guarantee_online_cpus_mems_in_subtree().
+ * track what's online after any CPU or memory node hotplug or unplug event.
*
* Since there are two callers of this routine, one for CPU hotplug
* events and one for memory node hotplug events, we could have coded
static void common_cpu_mem_hotplug_unplug(void)
{
cgroup_lock();
- mutex_lock(&callback_mutex);
- guarantee_online_cpus_mems_in_subtree(&top_cpuset);
top_cpuset.cpus_allowed = cpu_online_map;
top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
+ scan_for_empty_cpusets(&top_cpuset);
- mutex_unlock(&callback_mutex);
cgroup_unlock();
}
projects / karo-tx-linux.git / commitdiff