Re: [PATCH v3 2/2] mm: Tidy up shmem mTHP controls and stats

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 2024/9/2 17:58, Ryan Roberts wrote:
> Hi Baolin,
> 
> Thanks for the review - I've been out on Paternity leave so only getting around
> to replying now...

No worries :)

> On 09/08/2024 09:31, Baolin Wang wrote:
>>
>>
>> On 2024/8/8 19:18, Ryan Roberts wrote:
>>> Previously we had a situation where shmem mTHP controls and stats were
>>> not exposed for some supported sizes and were exposed for some
>>> unsupported sizes. So let's clean that up.
>>>
>>> Anon mTHP can support all large orders [2, PMD_ORDER]. But shmem can
>>> support all large orders [1, MAX_PAGECACHE_ORDER]. However, per-size
>>> shmem controls and stats were previously being exposed for all the anon
>>> mTHP orders, meaning order-1 was not present, and for arm64 64K base
>>> pages, orders 12 and 13 were exposed but were not supported internally.
>>>
>>> Tidy this all up by defining ctrl and stats attribute groups for anon
>>> and file separately. Anon ctrl and stats groups are populated for all
>>> orders in THP_ORDERS_ALL_ANON and file ctrl and stats groups are
>>> populated for all orders in THP_ORDERS_ALL_FILE_DEFAULT.
>>>
>>> Additionally, create "any" ctrl and stats attribute groups which are
>>> populated for all orders in (THP_ORDERS_ALL_ANON |
>>> THP_ORDERS_ALL_FILE_DEFAULT). swpout stats use this since they apply to
>>> anon and shmem.
>>>
>>> The side-effect of all this is that different hugepage-*kB directories
>>> contain different sets of controls and stats, depending on which memory
>>> types support that size. This approach is preferred over the
>>> alternative, which is to populate dummy controls and stats for memory
>>> types that do not support a given size.
>>>
>>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>>> ---
>>>    mm/huge_memory.c | 144 +++++++++++++++++++++++++++++++++++++----------
>>>    1 file changed, 114 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>> index 0c3075ee00012..082d86b7c6c2f 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -482,8 +482,8 @@ static void thpsize_release(struct kobject *kobj);
>>>    static DEFINE_SPINLOCK(huge_anon_orders_lock);
>>>    static LIST_HEAD(thpsize_list);
>>>    -static ssize_t thpsize_enabled_show(struct kobject *kobj,
>>> -                    struct kobj_attribute *attr, char *buf)
>>> +static ssize_t anon_enabled_show(struct kobject *kobj,
>>> +                 struct kobj_attribute *attr, char *buf)
>>>    {
>>>        int order = to_thpsize(kobj)->order;
>>>        const char *output;
>>> @@ -500,9 +500,9 @@ static ssize_t thpsize_enabled_show(struct kobject *kobj,
>>>        return sysfs_emit(buf, "%s\n", output);
>>>    }
>>>    -static ssize_t thpsize_enabled_store(struct kobject *kobj,
>>> -                     struct kobj_attribute *attr,
>>> -                     const char *buf, size_t count)
>>> +static ssize_t anon_enabled_store(struct kobject *kobj,
>>> +                  struct kobj_attribute *attr,
>>> +                  const char *buf, size_t count)
>>>    {
>>>        int order = to_thpsize(kobj)->order;
>>>        ssize_t ret = count;
>>> @@ -544,19 +544,35 @@ static ssize_t thpsize_enabled_store(struct kobject *kobj,
>>>        return ret;
>>>    }
>>>    -static struct kobj_attribute thpsize_enabled_attr =
>>> -    __ATTR(enabled, 0644, thpsize_enabled_show, thpsize_enabled_store);
>>> +static struct kobj_attribute anon_enabled_attr =
>>> +    __ATTR(enabled, 0644, anon_enabled_show, anon_enabled_store);
>>>    -static struct attribute *thpsize_attrs[] = {
>>> -    &thpsize_enabled_attr.attr,
>>> +static struct attribute *anon_ctrl_attrs[] = {
>>> +    &anon_enabled_attr.attr,
>>> +    NULL,
>>> +};
>>> +
>>> +static const struct attribute_group anon_ctrl_attr_grp = {
>>> +    .attrs = anon_ctrl_attrs,
>>> +};
>>> +
>>> +static struct attribute *file_ctrl_attrs[] = {
>>>    #ifdef CONFIG_SHMEM
>>>        &thpsize_shmem_enabled_attr.attr,
>>>    #endif
>>>        NULL,
>>>    };
>>>    -static const struct attribute_group thpsize_attr_group = {
>>> -    .attrs = thpsize_attrs,
>>> +static const struct attribute_group file_ctrl_attr_grp = {
>>> +    .attrs = file_ctrl_attrs,
>>> +};
>>> +
>>> +static struct attribute *any_ctrl_attrs[] = {
>>> +    NULL,
>>> +};
>>> +
>>> +static const struct attribute_group any_ctrl_attr_grp = {
>>> +    .attrs = any_ctrl_attrs,
>>>    };
>>
>> I wonder why adding a NULL group?
> 
> It made everything a bit more generic and therefore extensible. Its my
> preference to leave it as is, but will remove it if you insist.

My preference is we should add it when necessary, but but I don't have a 
strong opinion. Let's see what other guys prefer, David, Barry?