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 <[email protected]> --- kernel/cgroup/cgroup-internal.h | 5 ++++- kernel/cgroup/cgroup-v1.c | 2 +- kernel/cgroup/cgroup.c | 25 ++++++++++++++----------- 3 files changed, 19 insertions(+), 13 deletions(-) diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h index 5f8c8ac..9203bfb 100644 --- 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 7a965f4..fc34bcf 100644 --- 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 f90554d..69ad5b3 100644 --- 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 @@ int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx) * 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 @@ int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx) * 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); -- 2.9.3
