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    SubjectRe: [External] Re: [PATCH v7 06/15] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two
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    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@redhat.com> 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@bytedance.com>
    >>>> ---
    >>>> 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

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