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SubjectRe: [RFC] mm/vmstat: Add events for HugeTLB migration
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On 09/29/2020 03:34 AM, Mike Kravetz wrote:
> On 9/25/20 2:12 AM, Anshuman Khandual wrote:
>> Add following new vmstat events which will track HugeTLB page migration.
>>
>> 1. HUGETLB_MIGRATION_SUCCESS
>> 2. HUGETLB_MIGRATION_FAILURE
>>
>> It follows the existing semantics to accommodate HugeTLB subpages in total
>> page migration statistics. While here, this updates current trace event
>> "mm_migrate_pages" to accommodate now available HugeTLB based statistics.
>
> Thanks. This makes sense with recent THP changes.
>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 3ab965f83029..d53dd101ffff 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1415,13 +1415,17 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>> {
>> int retry = 1;
>> int thp_retry = 1;
>> + int hugetlb_retry = 1;
>> int nr_failed = 0;
>> int nr_succeeded = 0;
>> int nr_thp_succeeded = 0;
>> int nr_thp_failed = 0;
>> int nr_thp_split = 0;
>> + int nr_hugetlb_succeeded = 0;
>> + int nr_hugetlb_failed = 0;
>> int pass = 0;
>> bool is_thp = false;
>> + bool is_hugetlb = false;
>> struct page *page;
>> struct page *page2;
>> int swapwrite = current->flags & PF_SWAPWRITE;
>> @@ -1433,6 +1437,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>> for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {
>> retry = 0;
>> thp_retry = 0;
>> + hugetlb_retry = 0;
>>
>> list_for_each_entry_safe(page, page2, from, lru) {
>> retry:
>> @@ -1442,7 +1447,12 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>> * during migration.
>> */
>> is_thp = PageTransHuge(page) && !PageHuge(page);
>> + is_hugetlb = PageTransHuge(page) && PageHuge(page);
>
> PageHuge does not depend on PageTransHuge. So, this could just be
> is_hugetlb = PageHuge(page);

Sure.

>
> Actually, the current version of PageHuge is more expensive than PageTransHuge.
> So, the most optimal way to set these would be something like.
> if (PageTransHuge(page))
> if (PageHuge(page))
> is_hugetlb = true;
> else
> is_thp = true;
>
> Although, the compiler may be able to optimize. I did not check.

Both is_hugetlb and is_thp need to have either a true or false value
during each iteration as they are not getting reset otherwise. Hence
basically it should either be

is_thp = PageTransHuge(page) && !PageHuge(page);
is_hugetlb = PageHuge(page);

OR

is_hugetlb = false;
is_thp = false;
if (PageTransHuge(page))
if (PageHuge(page))
is_hugetlb = true;
else
is_thp = true;
}

>
>> +
>> nr_subpages = thp_nr_pages(page);
>> + if (is_hugetlb)
>> + nr_subpages = pages_per_huge_page(page_hstate(page));
>
> Can we just use compound_order() here for all cases?

Sure but we could also directly use compound_nr().

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