On 04/09/2013 07:46 AM, Kamezawa Hiroyuki wrote:
> (2013/04/09 12:18), 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.
>>
> Hmm. but the name is not lost, right ?
> How about returning error rather than making a mixture of lines in different formats ?
>
I still think it would be preferable to dump as much informative data as
we can. Even if the name is lost, a lot of info can still be present
(from the caches, etc).
The format also should not matter. Nobody will be script-processing this.
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