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SubjectRe: [RFC] mm/vmstat: Add events for HugeTLB migration
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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);

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.

> +
> 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?

--
Mike Kravetz

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