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authorTejun Heo <tj@kernel.org>2014-02-25 10:04:01 -0500
committerTejun Heo <tj@kernel.org>2014-02-25 10:04:01 -0500
commitc75611282cf1bf717c1866e7a7eb4d0743815187 (patch)
tree4579606847463892cc65977a55bee386b2b5cf2a /kernel/cgroup.c
parentf153ad11bca27996a5e8e1782557e36e80b03a8c (diff)
cgroup: add css_set->mg_tasks
Currently, while migrating tasks from one cgroup to another, cgroup_attach_task() builds a flex array of all target tasks; unfortunately, this has a couple issues. * Flex array has size limit. On 64bit, struct task_and_cgroup is 24bytes making the flex element limit around 87k. It is a high number but not impossible to hit. This means that the current cgroup implementation can't migrate a process with more than 87k threads. * Process migration involves memory allocation whose size is dependent on the number of threads the process has. This means that cgroup core can't guarantee success or failure of multi-process migrations as memory allocation failure can happen in the middle. This is in part because cgroup can't grab threadgroup locks of multiple processes at the same time, so when there are multiple processes to migrate, it is imposible to tell how many tasks are to be migrated beforehand. Note that this already affects cgroup_transfer_tasks(). cgroup currently cannot guarantee atomic success or failure of the operation. It may fail in the middle and after such failure cgroup doesn't have enough information to roll back properly. It just aborts with some tasks migrated and others not. To resolve the situation, we're going to use task->cg_list during migration too. Instead of building a separate array, target tasks will be linked into a dedicated migration list_head on the owning css_set. Tasks on the migration list are treated the same as tasks on the usual tasks list; however, being on a separate list allows cgroup migration code path to keep track of the target tasks by simply keeping the list of css_sets with tasks being migrated, making unpredictable dynamic allocation unnecessary. In prepartion of such migration path update, this patch introduces css_set->mg_tasks list and updates css_set task iterations so that they walk both css_set->tasks and ->mg_tasks. Note that ->mg_tasks isn't used yet. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c56
1 files changed, 37 insertions, 19 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8ab800c7bac..b80c611ff83 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -644,6 +644,7 @@ static struct css_set *find_css_set(struct css_set *old_cset,
atomic_set(&cset->refcount, 1);
INIT_LIST_HEAD(&cset->cgrp_links);
INIT_LIST_HEAD(&cset->tasks);
+ INIT_LIST_HEAD(&cset->mg_tasks);
INIT_HLIST_NODE(&cset->hlist);
/* Copy the set of subsystem state objects generated in
@@ -2590,9 +2591,14 @@ static void css_advance_task_iter(struct css_task_iter *it)
}
link = list_entry(l, struct cgrp_cset_link, cset_link);
cset = link->cset;
- } while (list_empty(&cset->tasks));
+ } while (list_empty(&cset->tasks) && list_empty(&cset->mg_tasks));
+
it->cset_link = l;
- it->task = cset->tasks.next;
+
+ if (!list_empty(&cset->tasks))
+ it->task = cset->tasks.next;
+ else
+ it->task = cset->mg_tasks.next;
}
/**
@@ -2636,24 +2642,29 @@ struct task_struct *css_task_iter_next(struct css_task_iter *it)
{
struct task_struct *res;
struct list_head *l = it->task;
- struct cgrp_cset_link *link;
+ struct cgrp_cset_link *link = list_entry(it->cset_link,
+ struct cgrp_cset_link, cset_link);
/* If the iterator cg is NULL, we have no tasks */
if (!it->cset_link)
return NULL;
res = list_entry(l, struct task_struct, cg_list);
- /* Advance iterator to find next entry */
+
+ /*
+ * Advance iterator to find next entry. cset->tasks is consumed
+ * first and then ->mg_tasks. After ->mg_tasks, we move onto the
+ * next cset.
+ */
l = l->next;
- link = list_entry(it->cset_link, struct cgrp_cset_link, cset_link);
- if (l == &link->cset->tasks) {
- /*
- * We reached the end of this task list - move on to the
- * next cgrp_cset_link.
- */
+
+ if (l == &link->cset->tasks)
+ l = link->cset->mg_tasks.next;
+
+ if (l == &link->cset->mg_tasks)
css_advance_task_iter(it);
- } else {
+ else
it->task = l;
- }
+
return res;
}
@@ -4502,16 +4513,23 @@ static int cgroup_css_links_read(struct seq_file *seq, void *v)
struct css_set *cset = link->cset;
struct task_struct *task;
int count = 0;
+
seq_printf(seq, "css_set %p\n", cset);
+
list_for_each_entry(task, &cset->tasks, cg_list) {
- if (count++ > MAX_TASKS_SHOWN_PER_CSS) {
- seq_puts(seq, " ...\n");
- break;
- } else {
- seq_printf(seq, " task %d\n",
- task_pid_vnr(task));
- }
+ if (count++ > MAX_TASKS_SHOWN_PER_CSS)
+ goto overflow;
+ seq_printf(seq, " task %d\n", task_pid_vnr(task));
+ }
+
+ list_for_each_entry(task, &cset->mg_tasks, cg_list) {
+ if (count++ > MAX_TASKS_SHOWN_PER_CSS)
+ goto overflow;
+ seq_printf(seq, " task %d\n", task_pid_vnr(task));
}
+ continue;
+ overflow:
+ seq_puts(seq, " ...\n");
}
up_read(&css_set_rwsem);
return 0;