Re: gigantic hugepages vs. movable zones

Aneesh Kumar K.V
2017-07-27T02:22:38Z

Michal Hocko <mhocko@kernel.org> writes:

> Hi,
> I've just noticed that alloc_gigantic_page ignores movability of the
> gigantic page and it uses any existing zone. Considering that
> hugepage_migration_supported only supports 2MB and pgd level hugepages
> then 1GB pages are not migratable and as such allocating them from a
> movable zone will break the basic expectation of this zone. Standard
> hugetlb allocations try to avoid that by using htlb_alloc_mask and I
> believe we should do the same for gigantic pages as well.
>
> I suspect this behavior is not intentional. What do you think about the
> following untested patch?

I also noticed an unrelated issue with the usage of
start_isolate_page_range. On error we set the migrate type to
MIGRATE_MOVABLE. That may conflict with CMA pages ? Wondering whether
we should check for page's pageblock migrate type in
pfn_range_valid_gigantic() ?

-aneesh