On 04/09/2013 07:18 AM, 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;
>>> +
>>> + /*
>>> + * 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);
>>>
>>
>> I'm sorry for dawm question ...when this error happens ?
>> We may get ENAMETOOLONG even with PAGE_SIZE(>=4096bytes) buffer ?
>>
>
> It does no harm to check the return value, and we don't have to
> worry about if cgroup_path() will be changed to return some other
> errno like ENOMEM in the future.
>
I feel more comfortable with the check as well. This is a debugging
interface after all. People tend to resort to this when things go wrong.
So at this point the less assumptions we make, the better.
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