Re: gigantic hugepages vs. movable zones

[Michal Hocko]

On Thu 27-07-17 13:30:31, Aneesh Kumar K.V wrote:
> 
> 
> 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@xxxxxxxxxx> 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 ?

I do not see an immediate problem. GFP_KERNEL allocations can fallback
to movable migrate pageblocks AFAIR. But I am not very much familiar
with migratetypes. Vlastimil, could you have a look please?
-- 
Michal Hocko
SUSE Labs