From 9395a4500404e05173eda9a2d198b6fa500e90c5 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 14 May 2014 09:15:02 -0400 Subject: [PATCH] cgroup: enable refcnting for root csses Currently, css_get(), css_tryget() and css_tryget_online() are noops for root csses as an optimization; however, we're planning to use css refcnts to track of cgroup lifetime too and root cgroups also need to be reference counted. Since css has been converted to percpu_refcnt, the overhead of refcnting is miniscule and this optimization isn't too meaningful anymore. Furthermore, controllers which optimize the root cgroup often never even invoke these functions in their hot paths. This patch enables refcnting for root csses too. This makes CSS_ROOT flag unused and removes it. Signed-off-by: Tejun Heo Acked-by: Li Zefan --- include/linux/cgroup.h | 10 ++-------- kernel/cgroup.c | 6 +++--- 2 files changed, 5 insertions(+), 11 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 160fcc69149e..286e39e4e9bf 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -77,7 +77,6 @@ struct cgroup_subsys_state { /* bits in struct cgroup_subsys_state flags field */ enum { - CSS_ROOT = (1 << 0), /* this CSS is the root of the subsystem */ CSS_ONLINE = (1 << 1), /* between ->css_online() and ->css_offline() */ }; @@ -89,9 +88,7 @@ enum { */ static inline void css_get(struct cgroup_subsys_state *css) { - /* We don't need to reference count the root state */ - if (!(css->flags & CSS_ROOT)) - percpu_ref_get(&css->refcnt); + percpu_ref_get(&css->refcnt); } /** @@ -106,8 +103,6 @@ static inline void css_get(struct cgroup_subsys_state *css) */ static inline bool css_tryget_online(struct cgroup_subsys_state *css) { - if (css->flags & CSS_ROOT) - return true; return percpu_ref_tryget_live(&css->refcnt); } @@ -119,8 +114,7 @@ static inline bool css_tryget_online(struct cgroup_subsys_state *css) */ static inline void css_put(struct cgroup_subsys_state *css) { - if (!(css->flags & CSS_ROOT)) - percpu_ref_put(&css->refcnt); + percpu_ref_put(&css->refcnt); } /* bits in struct cgroup flags field */ diff --git a/kernel/cgroup.c b/kernel/cgroup.c index e694f4153edb..cb5864e36f99 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4158,8 +4158,6 @@ static void init_and_link_css(struct cgroup_subsys_state *css, if (cgrp->parent) { css->parent = cgroup_css(cgrp->parent, ss); css_get(css->parent); - } else { - css->flags |= CSS_ROOT; } BUG_ON(cgroup_css(cgrp, ss)); @@ -4582,9 +4580,10 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early) BUG_ON(IS_ERR(css)); init_and_link_css(css, ss, &cgrp_dfl_root.cgrp); if (early) { - /* idr_alloc() can't be called safely during early init */ + /* allocation can't be done safely during early init */ css->id = 1; } else { + BUG_ON(percpu_ref_init(&css->refcnt, css_release)); css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL); BUG_ON(css->id < 0); } @@ -4671,6 +4670,7 @@ int __init cgroup_init(void) struct cgroup_subsys_state *css = init_css_set.subsys[ss->id]; + BUG_ON(percpu_ref_init(&css->refcnt, css_release)); css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL); BUG_ON(css->id < 0); -- 2.20.1