On Mon 08-04-13 14:36:52, Li Zefan wrote:
[...]
> @@ -5188,12 +5154,28 @@ static int mem_cgroup_dangling_read(struct cgroup *cont, struct cftype *cft,
> struct seq_file *m)
> {
> struct mem_cgroup *memcg;
> + char *memcg_name;
> + int ret;
The interface is only for debugging, all right, but that doesn't mean we
should allocate a buffer for each read. Why cannot we simply use
cgroup_path for seq_printf directly? Can we still race with the group
rename?
> +
> + /*
> + * cgroup.c will do page-sized allocations most of the time,
> + * so we'll just follow the pattern. Also, __get_free_pages
> + * is a better interface than kmalloc for us here, because
> + * we'd like this memory to be always billed to the root cgroup,
> + * not to the process removing the memcg. While kmalloc would
> + * require us to wrap it into memcg_stop/resume_kmem_account,
> + * with __get_free_pages we just don't pass the memcg flag.
> + */
> + memcg_name = (char *)__get_free_pages(GFP_KERNEL, 0);
> + if (!memcg_name)
> + return -ENOMEM;
>
> mutex_lock(&dangling_memcgs_mutex);
>
> list_for_each_entry(memcg, &dangling_memcgs, dead) {
> - if (memcg->memcg_name)
> - seq_printf(m, "%s:\n", memcg->memcg_name);
> + ret = cgroup_path(memcg->css.cgroup, memcg_name, PAGE_SIZE);
> + if (!ret)
> + seq_printf(m, "%s:\n", memcg_name);
> else
> seq_printf(m, "%p (name lost):\n", memcg);
>
> @@ -5203,6 +5185,7 @@ static int mem_cgroup_dangling_read(struct cgroup *cont, struct cftype *cft,
> }
>
> mutex_unlock(&dangling_memcgs_mutex);
> + free_pages((unsigned long)memcg_name, 0);
> return 0;
> }
> #endif
> --
> 1.8.0.2
> --
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--
Michal Hocko
SUSE Labs
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