Re: [External] Re: [PATCH v7 06/15] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two

[David Hildenbrand]

On 09.12.20 11:06, David Hildenbrand wrote:
> On 09.12.20 11:03, Muchun Song wrote:
>> On Wed, Dec 9, 2020 at 5:57 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>>>
>>> On 30.11.20 16:18, Muchun Song wrote:
>>>> We only can free the tail vmemmap pages of HugeTLB to the buddy allocator
>>>> when the size of struct page is a power of two.
>>>>
>>>> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
>>>> ---
>>>>  mm/hugetlb_vmemmap.c | 5 +++++
>>>>  1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
>>>> index 51152e258f39..ad8fc61ea273 100644
>>>> --- a/mm/hugetlb_vmemmap.c
>>>> +++ b/mm/hugetlb_vmemmap.c
>>>> @@ -111,6 +111,11 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
>>>>       unsigned int nr_pages = pages_per_huge_page(h);
>>>>       unsigned int vmemmap_pages;
>>>>
>>>> +     if (!is_power_of_2(sizeof(struct page))) {
>>>> +             pr_info("disable freeing vmemmap pages for %s\n", h->name);
>>>
>>> I'd just drop that pr_info(). Users are able to observe that it's
>>> working (below), so they are able to identify that it's not working as well.
>>
>> The below is just a pr_debug. Do you suggest converting it to pr_info?
> 
> Good question. I wonder if users really have to know in most cases.
> Maybe pr_debug() is good enough in environments where we want to debug
> why stuff is not working as expected.
> 

Oh, another thought, can we glue availability of
HUGETLB_PAGE_FREE_VMEMMAP (or a new define based on the config and the
size of a stuct page) to the size of struct page somehow?

I mean, it's known at compile time that this will never work.

-- 
Thanks,

David / dhildenb