Re: [External] Re: [PATCH v5 13/21] mm/hugetlb: Use PG_slab to indicate split pmd

[Michal Hocko]

On Fri 20-11-20 17:30:27, Muchun Song wrote:
> On Fri, Nov 20, 2020 at 4:16 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
> >
> > On Fri 20-11-20 14:43:17, Muchun Song wrote:
> > > When we allocate hugetlb page from buddy, we may need split huge pmd
> > > to pte. When we free the hugetlb page, we can merge pte to pmd. So
> > > we need to distinguish whether the previous pmd has been split. The
> > > page table is not allocated from slab. So we can reuse the PG_slab
> > > to indicate that the pmd has been split.
> >
> > PageSlab is used outside of the slab allocator proper and that code
> > might get confused by this AFAICS.
> 
> I got your concerns. Maybe we can use PG_private instead of the
> PG_slab.

Reusing a page flag arbitrarily is not that easy. Hugetlb pages have a
lot of spare room in struct page so I would rather use something else.
-- 
Michal Hocko
SUSE Labs