On Thu 24-04-14 17:02:09, Tejun Heo wrote: > Currently, cgroup->id is allocated from 0, which is always assigned to > the root cgroup; unfortunately, memcg wants to use ID 0 to indicate > invalid IDs and ends up incrementing all IDs by one. > > It's reasonable to reserve 0 for special purposes. This patch updates > cgroup core so that ID 0 is not used and the root cgroups get ID 1. > The ID incrementing is removed form memcg. > > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxx> Sorry for a late response. Thanks for removing this hack from memcg! cgroup code change looks good at first glance but I am not familiar with all the recent changes so I do not feel to add my Reviewed-by. Anyway Acked-by: Michal Hocko <mhocko@xxxxxxx> for the change in the semantic and the memcg change. Thanks! > --- > include/linux/cgroup.h | 4 ++-- > kernel/cgroup.c | 4 ++-- > mm/memcontrol.c | 8 ++------ > 3 files changed, 6 insertions(+), 10 deletions(-) > > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h > index c6c703f..793f70a 100644 > --- a/include/linux/cgroup.h > +++ b/include/linux/cgroup.h > @@ -144,8 +144,8 @@ struct cgroup { > /* > * idr allocated in-hierarchy ID. > * > - * The ID of the root cgroup is always 0, and a new cgroup > - * will be assigned with a smallest available ID. > + * ID 0 is not used, the ID of the root cgroup is always 1, and a > + * new cgroup will be assigned with a smallest available ID. > * > * Allocating/Removing ID must be protected by cgroup_mutex. > */ > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 21667f3..3fa0463 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -1531,7 +1531,7 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned int ss_mask) > lockdep_assert_held(&cgroup_tree_mutex); > lockdep_assert_held(&cgroup_mutex); > > - ret = idr_alloc(&root->cgroup_idr, root_cgrp, 0, 1, GFP_KERNEL); > + ret = idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL); > if (ret < 0) > goto out; > root_cgrp->id = ret; > @@ -4225,7 +4225,7 @@ static long cgroup_create(struct cgroup *parent, const char *name, > * Temporarily set the pointer to NULL, so idr_find() won't return > * a half-baked cgroup. > */ > - cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 1, 0, GFP_KERNEL); > + cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL); > if (cgrp->id < 0) { > err = -ENOMEM; > goto err_unlock; > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 29501f0..1d0b297 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -527,18 +527,14 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) > > static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg) > { > - /* > - * The ID of the root cgroup is 0, but memcg treat 0 as an > - * invalid ID, so we return (cgroup_id + 1). > - */ > - return memcg->css.cgroup->id + 1; > + return memcg->css.cgroup->id; > } > > static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id) > { > struct cgroup_subsys_state *css; > > - css = css_from_id(id - 1, &memory_cgrp_subsys); > + css = css_from_id(id, &memory_cgrp_subsys); > return mem_cgroup_from_css(css); > } > > -- > 1.9.0 > -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html