cgroup: call subsys->*attach() only for subsystems which are actually affected by...

Currently, subsys->*attach() callbacks are called for all subsystems
which are attached to the hierarchy on which the migration is taking
place.

With cgroup_migrate_prepare_dst() filtering out identity migrations,
v1 hierarchies can avoid spurious ->*attach() callback invocations
where the source and destination csses are identical; however, this
isn't enough on v2 as only a subset of the attached controllers can be
affected on controller enable/disable.

While spurious ->*attach() invocations aren't critically broken,
they're unnecessary overhead and can lead to temporary overcharges on
certain controllers.  Fix it by tracking which subsystems are affected
by a migration and invoking ->*attach() callbacks only on those
subsystems.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>

diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 5f8c8ac5ab88360ecc7739d350d4efb20416e377..9203bfb0560399af9611bd40516758ab01076cba 100644 (file)
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -62,6 +62,9 @@ struct cgroup_mgctx {
 
        /* tasks and csets to migrate */
        struct cgroup_taskset   tset;
+
+       /* subsystems affected by migration */
+       u16                     ss_mask;
 };
 
 #define CGROUP_TASKSET_INIT(tset)                                              \
@@ -172,7 +175,7 @@ void cgroup_migrate_add_src(struct css_set *src_cset, struct cgroup *dst_cgrp,
                            struct cgroup_mgctx *mgctx);
 int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx);
 int cgroup_migrate(struct task_struct *leader, bool threadgroup,
-                  struct cgroup_mgctx *mgctx, struct cgroup_root *root);
+                  struct cgroup_mgctx *mgctx);
 
 int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
                       bool threadgroup);

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 7a965f460faf9e898ec50ec476556c249871eb0b..fc34bcf2329f4dbc625ce2e3579a9454fb0ce5e5 100644 (file)
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -125,7 +125,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
                css_task_iter_end(&it);
 
                if (task) {
-                       ret = cgroup_migrate(task, false, &mgctx, to->root);
+                       ret = cgroup_migrate(task, false, &mgctx);
                        if (!ret)
                                trace_cgroup_transfer_tasks(to, task, false);
                        put_task_struct(task);

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index f90554d24e591e451ce809926fe2a9847376a06a..69ad5b3de0c1b94545600e909fbae2bc8cd72d01 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2019,15 +2019,13 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
 /**
  * cgroup_taskset_migrate - migrate a taskset
  * @mgctx: migration context
- * @root: cgroup root the migration is taking place on
  *
  * Migrate tasks in @mgctx as setup by migration preparation functions.
  * This function fails iff one of the ->can_attach callbacks fails and
  * guarantees that either all or none of the tasks in @mgctx are migrated.
  * @mgctx is consumed regardless of success.
  */
-static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx,
-                                 struct cgroup_root *root)
+static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
 {
        struct cgroup_taskset *tset = &mgctx->tset;
        struct cgroup_subsys *ss;
@@ -2040,7 +2038,7 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx,
                return 0;
 
        /* check that we can legitimately attach to the cgroup */
-       do_each_subsys_mask(ss, ssid, root->subsys_mask) {
+       do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
                if (ss->can_attach) {
                        tset->ssid = ssid;
                        ret = ss->can_attach(tset);
@@ -2076,7 +2074,7 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx,
         */
        tset->csets = &tset->dst_csets;
 
-       do_each_subsys_mask(ss, ssid, root->subsys_mask) {
+       do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
                if (ss->attach) {
                        tset->ssid = ssid;
                        ss->attach(tset);
@@ -2087,7 +2085,7 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx,
        goto out_release_tset;
 
 out_cancel_attach:
-       do_each_subsys_mask(ss, ssid, root->subsys_mask) {
+       do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
                if (ssid == failed_ssid)
                        break;
                if (ss->cancel_attach) {
@@ -2223,6 +2221,8 @@ int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
        list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,
                                 mg_preload_node) {
                struct css_set *dst_cset;
+               struct cgroup_subsys *ss;
+               int ssid;
 
                dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
                if (!dst_cset)
@@ -2251,6 +2251,10 @@ int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx)
                                      &mgctx->preloaded_dst_csets);
                else
                        put_css_set(dst_cset);
+
+               for_each_subsys(ss, ssid)
+                       if (src_cset->subsys[ssid] != dst_cset->subsys[ssid])
+                               mgctx->ss_mask |= 1 << ssid;
        }
 
        return 0;
@@ -2263,7 +2267,6 @@ err:
  * cgroup_migrate - migrate a process or task to a cgroup
  * @leader: the leader of the process or the task to migrate
  * @threadgroup: whether @leader points to the whole process or a single task
- * @root: cgroup root migration is taking place on
  * @mgctx: migration context
  *
  * Migrate a process or task denoted by @leader.  If migrating a process,
@@ -2279,7 +2282,7 @@ err:
  * actually starting migrating.
  */
 int cgroup_migrate(struct task_struct *leader, bool threadgroup,
-                  struct cgroup_mgctx *mgctx, struct cgroup_root *root)
+                  struct cgroup_mgctx *mgctx)
 {
        struct task_struct *task;
 
@@ -2299,7 +2302,7 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup,
        rcu_read_unlock();
        spin_unlock_irq(&css_set_lock);
 
-       return cgroup_migrate_execute(mgctx, root);
+       return cgroup_migrate_execute(mgctx);
 }
 
 /**
@@ -2335,7 +2338,7 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
        /* prepare dst csets and commit */
        ret = cgroup_migrate_prepare_dst(&mgctx);
        if (!ret)
-               ret = cgroup_migrate(leader, threadgroup, &mgctx, dst_cgrp->root);
+               ret = cgroup_migrate(leader, threadgroup, &mgctx);
 
        cgroup_migrate_finish(&mgctx);
 
@@ -2539,7 +2542,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
        }
        spin_unlock_irq(&css_set_lock);
 
-       ret = cgroup_migrate_execute(&mgctx, cgrp->root);
+       ret = cgroup_migrate_execute(&mgctx);
 out_finish:
        cgroup_migrate_finish(&mgctx);
        percpu_up_write(&cgroup_threadgroup_rwsem);