Re: gigantic hugepages vs. movable zones

Aneesh Kumar K.V
2017-07-27T08:00:39Z

On 07/27/2017 12:58 PM, Michal Hocko wrote:
> On Thu 27-07-17 07:52:08, Aneesh Kumar K.V wrote:
>> 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.
>
> Why that should be a problem? I think it is perfectly OK to have
> MIGRATE_MOVABLE pageblocks inside kernel zones.
>

we can pick pages with migrate type movable and if we fail to isolate
won't we set the migrate type of that pages to MOVABLE ?

-aneesh