Re: [PATCH v1 2/2] mm: mTHP stats for pagecache folio allocations

Baolin Wang
2024-07-13T12:54:16Z

On 2024/7/13 19:00, Ryan Roberts wrote:
> [...]
>
>>> +static int thpsize_create(int order, struct kobject *parent)
>>>   {
>>>       unsigned long size = (PAGE_SIZE << order) / SZ_1K;
>>> +    struct thpsize_child *stats;
>>>       struct thpsize *thpsize;
>>>       int ret;
>>>   +    /*
>>> +     * Each child object (currently only "stats" directory) holds a
>>> +     * reference to the top-level thpsize object, so we can drop our ref to
>>> +     * the top-level once stats is setup. Then we just need to drop a
>>> +     * reference on any children to clean everything up. We can't just use
>>> +     * the attr group name for the stats subdirectory because there may be
>>> +     * multiple attribute groups to populate inside stats and overlaying
>>> +     * using the name property isn't supported in that way; each attr group
>>> +     * name, if provided, must be unique in the parent directory.
>>> +     */
>>> +
>>>       thpsize = kzalloc(sizeof(*thpsize), GFP_KERNEL);
>>> -    if (!thpsize)
>>> -        return ERR_PTR(-ENOMEM);
>>> +    if (!thpsize) {
>>> +        ret = -ENOMEM;
>>> +        goto err;
>>> +    }
>>> +    thpsize->order = order;
>>>         ret = kobject_init_and_add(&thpsize->kobj, &thpsize_ktype, parent,
>>>                      "hugepages-%lukB", size);
>>>       if (ret) {
>>>           kfree(thpsize);
>>> -        return ERR_PTR(ret);
>>> +        goto err;
>>>       }
>>>   -    ret = sysfs_create_group(&thpsize->kobj, &thpsize_attr_group);
>>> -    if (ret) {
>>> +    stats = kzalloc(sizeof(*stats), GFP_KERNEL);
>>> +    if (!stats) {
>>>           kobject_put(&thpsize->kobj);
>>> -        return ERR_PTR(ret);
>>> +        ret = -ENOMEM;
>>> +        goto err;
>>>       }
>>>   -    ret = sysfs_create_group(&thpsize->kobj, &stats_attr_group);
>>> +    ret = kobject_init_and_add(&stats->kobj, &thpsize_child_ktype,
>>> +                   &thpsize->kobj, "stats");
>>> +    kobject_put(&thpsize->kobj);
>>>       if (ret) {
>>> -        kobject_put(&thpsize->kobj);
>>> -        return ERR_PTR(ret);
>>> +        kfree(stats);
>>> +        goto err;
>>>       }
>>>   -    thpsize->order = order;
>>> -    return thpsize;
>>> +    if (BIT(order) & THP_ORDERS_ALL_ANON) {
>>> +        ret = sysfs_create_group(&thpsize->kobj, &thpsize_attr_group);
>>> +        if (ret)
>>> +            goto err_put;
>>> +
>>> +        ret = sysfs_create_group(&stats->kobj, &stats_attr_group);
>>> +        if (ret)
>>> +            goto err_put;
>>> +    }
>>> +
>>> +    if (BIT(order) & PAGECACHE_LARGE_ORDERS) {
>>> +        ret = sysfs_create_group(&stats->kobj, &file_stats_attr_group);
>>> +        if (ret)
>>> +            goto err_put;
>>> +    }
>>> +
>>> +    list_add(&stats->node, &thpsize_child_list);
>>> +    return 0;
>>> +err_put:
>>
>> IIUC, I think you should call 'sysfs_remove_group' to remove the group before
>> putting the kobject.
>
> Are you sure about that? As I understood it, sysfs_create_group() was
> conceptually modifying the state of the kobj, so when the kobj gets destroyed,
> all its state is tidied up. __kobject_del() (called on the last kobject_put())
> calls sysfs_remove_groups() and tidies up the sysfs state as far as I can see?

IIUC, __kobject_del() only removes the ktype defaut groups by
'sysfs_remove_groups(kobj, ktype->default_groups)', but your created
groups are not added into the ktype->default_groups. That means you
should mannuly remove them, or am I miss something?