Messages in this thread | | | Date | Tue, 3 Aug 2010 13:54:13 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH -mm 1/5] quick lookup memcg by ID |
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On Tue, 3 Aug 2010 13:51:29 +0900 Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> On Tue, 3 Aug 2010 13:37:23 +0900 > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > > On Tue, 3 Aug 2010 13:31:09 +0900 > > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > > > (snip) > > > > +/* 0 is unused */ > > > > +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; > > > > + > > > > +static struct mem_cgroup *id_to_memcg(unsigned short id) > > > > +{ > > > > + /* > > > > + * This array is set to NULL when mem_cgroup is freed. > > > > + * IOW, there are no more references && rcu_synchronized(). > > > > + * This lookup-caching is safe. > > > > + */ > > > > + if (unlikely(!mem_cgroups[id])) { > > > > + struct cgroup_subsys_state *css; > > > > + > > > > + rcu_read_lock(); > > > > + css = css_lookup(&mem_cgroup_subsys, id); > > > > + rcu_read_unlock(); > > > > + if (!css) > > > > + return NULL; > > > > + mem_cgroups[id] = container_of(css, struct mem_cgroup, css); > > > > + } > > > > + return mem_cgroups[id]; > > > > +} > > > id_to_memcg() seems to be called under rcu_read_lock() already, so I think > > > rcu_read_lock()/unlock() would be unnecessary. > > > > > > > Maybe. I thought about which is better to add > > > > VM_BUG_ON(!rcu_read_lock_held); > > or > > rcu_read_lock() > > .. > > rcu_read_unlock() > > > > Do you like former ? If so, it's ok to remove rcu-read-lock. > > > Yes, I personally like the former.
ok, will rewrite in that style.
-Kame
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