On Fri 24-08-18 12:03:14, Aneesh Kumar K.V wrote:
> When scanning for movable pages, filter out Hugetlb pages if hugepage migration
> is not supported. Without this we hit infinte loop in __offline pages where we
> do
> pfn = scan_movable_pages(start_pfn, end_pfn);
> if (pfn) { /* We have movable pages */
> ret = do_migrate_range(pfn, end_pfn);
> goto repeat;
> }
>
> We do support hugetlb migration ony if the hugetlb pages are at pmd level. Here
> we just check for Kernel config. The gigantic page size check is done in
> page_huge_active.
Well, this is a bit misleading. I would say that
Fix this by checking hugepage_migration_supported both in has_unmovable_pages
which is the primary backoff mechanism for page offlining and for
consistency reasons also into scan_movable_pages because it doesn't make
any sense to return a pfn to non-migrateable huge page.
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Reported-by: Haren Myneni <haren@xxxxxxxxxxxxxxxxxx>
> CC: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
I would add
Fixes: 72b39cfc4d75 ("mm, memory_hotplug: do not fail offlining too early")
Not because the bug has been introduced by that commit but rather
because the issue would be latent before that commit.
My Acked-by still holds.
> ---
> mm/memory_hotplug.c | 3 ++-
> mm/page_alloc.c | 4 ++++
> 2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 9eea6e809a4e..38d94b703e9d 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1333,7 +1333,8 @@ static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
> if (__PageMovable(page))
> return pfn;
> if (PageHuge(page)) {
> - if (page_huge_active(page))
> + if (hugepage_migration_supported(page_hstate(page)) &&
> + page_huge_active(page))
> return pfn;
> else
> pfn = round_up(pfn + 1,
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c677c1506d73..b8d91f59b836 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7709,6 +7709,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> * handle each tail page individually in migration.
> */
> if (PageHuge(page)) {
> +
> + if (!hugepage_migration_supported(page_hstate(page)))
> + goto unmovable;
> +
> iter = round_up(iter + 1, 1<<compound_order(page)) - 1;
> continue;
> }
> --
> 2.17.1
--
Michal Hocko
SUSE Labs
