Messages in this thread | | | Date | Mon, 23 Aug 2010 14:32:37 +0900 | From | Daisuke Nishimura <> | Subject | Re: [PATCH] memcg: use ID in page_cgroup |
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On Fri, 20 Aug 2010 19:01:32 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > I have an idea to remove page_cgroup->page pointer, 8bytes reduction per page. > But it will be after this work. Another off topic. I think we can reduce the size of mem_cgroup by packing some boolean members into one "unsinged long flags".
> @@ -300,12 +300,13 @@ static atomic_t mem_cgroup_num; > #define NR_MEMCG_GROUPS (CONFIG_MEM_CGROUP_MAX_GROUPS + 1) > static struct mem_cgroup *mem_cgroups[NR_MEMCG_GROUPS] __read_mostly; > > -/* Must be called under rcu_read_lock */ > -static struct mem_cgroup *id_to_memcg(unsigned short id) > +/* Must be called under rcu_read_lock, set safe==true if under lock */ Do you mean, "Set safe==true if we can ensure by some locks that the id can be safely dereferenced without rcu_read_lock", right ?
> +static struct mem_cgroup *id_to_memcg(unsigned short id, bool safe) > { > struct mem_cgroup *ret; > /* see mem_cgroup_free() */ > - ret = rcu_dereference_check(mem_cgroups[id], rch_read_lock_held()); > + ret = rcu_dereference_check(mem_cgroups[id], > + rch_read_lock_held() || safe); > if (likely(ret && ret->valid)) > return ret; > return NULL;
(snip) > @@ -723,6 +729,11 @@ static inline bool mem_cgroup_is_root(st > return (mem == root_mem_cgroup); > } > > +static inline bool mem_cgroup_is_rootid(unsigned short id) > +{ > + return (id == 1); > +} > + It might be better to add
BUG_ON(newid->id != 1)
in cgroup.c::cgroup_init_idr().
Thanks, Daisuke Nishimura.
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