Hi Zi,
On 09/18/2020 02:34 AM, Zi Yan wrote:
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> PageTransHuge returns true for both thp and hugetlb, so thp stats was
> counting both thp and hugetlb migrations. Exclude hugetlb migration by
> setting is_thp variable right.
Coincidentally, I had just detected this problem last evening and was
in the process of sending a patch this morning :) Nonetheless, thanks
for the patch.
Earlier there was a similar THP-HugeTLB ambiguity down the error path
as well. In hindsight, I should have noticed or remembered about this
earlier fix during the THP stats patch.
e6112fc30070 (mm/migrate.c: split only transparent huge pages when allocation fails)
>
> Clean up thp handling code too when we are there.
>
> Fixes: 1a5bae25e3cf ("mm/vmstat: add events for THP migration without split")
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
> mm/migrate.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 941b89383cf3..6bc9559afc70 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1445,7 +1445,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> * Capture required information that might get lost
> * during migration.
> */
> - is_thp = PageTransHuge(page);
> + is_thp = PageTransHuge(page) && !PageHuge(page);
> nr_subpages = thp_nr_pages(page);
> cond_resched();
>
> @@ -1471,7 +1471,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> * we encounter them after the rest of the list
> * is processed.
> */
> - if (PageTransHuge(page) && !PageHuge(page)) {
> + if (is_thp) {
> lock_page(page);
> rc = split_huge_page_to_list(page, from);
> unlock_page(page);
> @@ -1480,8 +1480,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> nr_thp_split++;
> goto retry;
> }
> - }
> - if (is_thp) {
> +
> nr_thp_failed++;
> nr_failed += nr_subpages;
> goto out;
>
Moving the failure path inside the split path makes sense, now
that it is already established that the page is indeed a THP.
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
