Re: [PATCH v5 2/4] mm: Introduce mem_cgroup_swapin_uncharge_swap_nr() helper for large folios swap-in

[Barry Song]

On Sat, Jul 27, 2024 at 4:31 AM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
>
> On Fri, Jul 26, 2024 at 2:47 AM Barry Song <21cnbao@xxxxxxxxx> wrote:
> >
> > From: Barry Song <v-songbaohua@xxxxxxxx>
> >
> > With large folios swap-in, we might need to uncharge multiple entries
> > all together, it is better to introduce a helper for that.
> >
> > Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> > ---
> >  include/linux/memcontrol.h | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 1b79760af685..55958cbce61b 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -684,6 +684,14 @@ int mem_cgroup_swapin_charge_folio(struct folio *folio, struct mm_struct *mm,
> >                                   gfp_t gfp, swp_entry_t entry);
> >  void mem_cgroup_swapin_uncharge_swap(swp_entry_t entry);
> >
> > +static inline void mem_cgroup_swapin_uncharge_swap_nr(swp_entry_t entry, int nr)
> > +{
> > +       int i;
> > +
> > +       for (i = 0; i < nr; i++, entry.val++)
> > +               mem_cgroup_swapin_uncharge_swap(entry);
>
> mem_cgroup_swapin_uncharge_swap() calls mem_cgroup_uncharge_swap()
> which already takes in nr_pages, but we currently only pass 1. Would
> it be better if we just make mem_cgroup_swapin_uncharge_swap() take in
> nr_pages as well and pass it along to mem_cgroup_uncharge_swap(),
> instead of calling it in a loop?
>
> This would batch the page counter, stats updates, and refcount updates
> in mem_cgroup_uncharge_swap(). You may be able to observe a bit of a
> performance gain with this.

Good suggestion. I'll send the v6 version below after waiting for some
comments on the other patches.