Re: [RFC PATCH v3 2/4] mm: distinguish large folio swap allocation failures

[Johannes Weiner]

On Tue, Jul 21, 2026 at 04:15:13PM +0800, Barry Song wrote:
> On Fri, Jul 17, 2026 at 8:25 PM Xueyuan Chen <xueyuan.chen21@xxxxxxxxx> wrote:
> > @@ -5495,6 +5497,9 @@ int __mem_cgroup_try_charge_swap(struct folio *folio, swp_entry_t entry)
> >         rcu_read_lock();
> >         memcg = obj_cgroup_memcg(objcg);
> >         if (!entry.val) {
> > +               if (nr_swap_pages && !mem_cgroup_is_root(memcg))
> > +                       *nr_swap_pages = min(*nr_swap_pages,
> > +                                            page_counter_margin(&memcg->swap));
> 
> This looks a bit odd. Could we decouple *nr_swap_pages from margin and
> have the function always return margin instead?
> 
> I don't think this function needs to care about the initial value returned by
> get_nr_swap_pages(). While folio_alloc_swap() may depend on it, they're
> different software layers, and we shouldn't couple them together.

Agreed!