Re: gigantic hugepages vs. movable zones

[Aneesh Kumar K.V]

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 ?

-aneesh