Messages in this thread | | | Date | Fri, 06 Feb 2009 10:07:40 +0800 | From | Li Zefan <> | Subject | Re: [RFC][PATCH] Reduce size of swap_cgroup by CSS ID |
| |
> +/* > + * A helper function to get mem_cgroup from ID. must be called under > + * rcu_read_lock(). Because css_tryget() is called under this, css_put > + * should be called later. > + */ > +static struct mem_cgroup *mem_cgroup_lookup_get(unsigned short id) > +{ > + struct cgroup_subsys_state *css; > + > + /* ID 0 is unused ID */ > + if (!id) > + return NULL; > + css = css_lookup(&mem_cgroup_subsys, id); > + if (css && css_tryget(css)) > + return container_of(css, struct mem_cgroup, css); > + return NULL; > +}
the returned mem_cgroup needn't be protected by rcu_read_lock(), so I think this is better: rcu_read_lock(); css = css_lookup(&mem_cgroup_subsys, id); rcu_read_unlock(); and no lock is needed when calling mem_cgroup_lookup_get().
> * Returns old value at success, NULL at failure. > * (Of course, old value can be NULL.) > */ > -struct mem_cgroup *swap_cgroup_record(swp_entry_t ent, struct mem_cgroup *mem) > +unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
kernel-doc needs to be updated
> * lookup_swap_cgroup - lookup mem_cgroup tied to swap entry > * @ent: swap entry to be looked up. > * > - * Returns pointer to mem_cgroup at success. NULL at failure. > + * Returns CSS ID of mem_cgroup at success. NULL at failure.
s/NULL/0/
> */ > -struct mem_cgroup *lookup_swap_cgroup(swp_entry_t ent) > +unsigned short lookup_swap_cgroup(swp_entry_t ent)
| |