Re: [External] Re: [PATCH v18 4/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page

[Muchun Song]

On Thu, Mar 11, 2021 at 4:46 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Thu 11-03-21 12:26:32, Muchun Song wrote:
> > On Wed, Mar 10, 2021 at 11:19 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
> > >
> > > On Mon 08-03-21 18:28:02, Muchun Song wrote:
> [...]
> > > > @@ -1771,8 +1813,12 @@ int dissolve_free_huge_page(struct page *page)
> > > >               h->free_huge_pages--;
> > > >               h->free_huge_pages_node[nid]--;
> > > >               h->max_huge_pages--;
> > > > -             update_and_free_page(h, head);
> > > > -             rc = 0;
> > > > +             rc = update_and_free_page(h, head);
> > > > +             if (rc) {
> > > > +                     h->surplus_huge_pages--;
> > > > +                     h->surplus_huge_pages_node[nid]--;
> > > > +                     h->max_huge_pages++;
> > >
> > > This is quite ugly and confusing. update_and_free_page is careful to do
> > > the proper counters accounting and now you just override it partially.
> > > Why cannot we rely on update_and_free_page do the right thing?
> >
> > Dissolving path is special here. Since update_and_free_page failed,
> > the number of surplus pages was incremented.  Surplus pages are
> > the number of pages greater than max_huge_pages.  Since we are
> > incrementing max_huge_pages, we should decrement (undo) the
> > addition to surplus_huge_pages and surplus_huge_pages_node[nid].
>
> Can we make dissolve_free_huge_page less special or tell
> update_and_free_page to not account against dissolve_free_huge_page?

Of course can.

Thanks.

> --
> Michal Hocko
> SUSE Labs