Re: [RFC][PATCH 6/9] mm/vmscan: add page demotion counter

[Yang Shi]

On Mon, Oct 19, 2020 at 12:38 AM Huang, Ying <ying.huang@xxxxxxxxx> wrote:
>
> Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> writes:
>
> > From: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> >
> > Account the number of demoted pages into reclaim_state->nr_demoted.
>
> It appears that you don't add "nr_demoted" into struct reclaim_state.
>
> > Add pgdemote_kswapd and pgdemote_direct VM counters showed in
> > /proc/vmstat.
> >
> > [ daveh:
> >    - __count_vm_events() a bit, and made them look at the THP
> >      size directly rather than getting data from migrate_pages()
>
> It appears that we get the data from migrate_pages() now.
>
> > ]
> >
> > Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> > Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > Cc: Huang Ying <ying.huang@xxxxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > ---
> >
> >  b/include/linux/vm_event_item.h |    2 ++
> >  b/mm/vmscan.c                   |    6 ++++++
> >  b/mm/vmstat.c                   |    2 ++
> >  3 files changed, 10 insertions(+)
> >
> > diff -puN include/linux/vm_event_item.h~mm-vmscan-add-page-demotion-counter include/linux/vm_event_item.h
> > --- a/include/linux/vm_event_item.h~mm-vmscan-add-page-demotion-counter       2020-10-07 09:15:32.171642439 -0700
> > +++ b/include/linux/vm_event_item.h   2020-10-07 09:15:32.179642439 -0700
> > @@ -33,6 +33,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PS
> >               PGREUSE,
> >               PGSTEAL_KSWAPD,
> >               PGSTEAL_DIRECT,
> > +             PGDEMOTE_KSWAPD,
> > +             PGDEMOTE_DIRECT,
> >               PGSCAN_KSWAPD,
> >               PGSCAN_DIRECT,
> >               PGSCAN_DIRECT_THROTTLE,
> > diff -puN mm/vmscan.c~mm-vmscan-add-page-demotion-counter mm/vmscan.c
> > --- a/mm/vmscan.c~mm-vmscan-add-page-demotion-counter 2020-10-07 09:15:32.173642439 -0700
> > +++ b/mm/vmscan.c     2020-10-07 09:15:32.180642439 -0700
> > @@ -147,6 +147,7 @@ struct scan_control {
> >               unsigned int immediate;
> >               unsigned int file_taken;
> >               unsigned int taken;
> > +             unsigned int demoted;
>
> It appears that this newly added field isn't used in the patch.

My original patch tracked nr_demoted in reclaim_stat as well, but it
seems Dave dropped that part. If Dave thinks it is not necessary to
keep tracking nr_demoted in reclaim_stat, then that field should be
dropped.

>
> >       } nr;
> >
> >       /* for recording the reclaimed slab by now */
> > @@ -1134,6 +1135,11 @@ static unsigned int demote_page_list(str
> >                           target_nid, MIGRATE_ASYNC, MR_DEMOTION,
> >                           &nr_succeeded);
> >
> > +     if (current_is_kswapd())
> > +             __count_vm_events(PGDEMOTE_KSWAPD, nr_succeeded);
> > +     else
> > +             __count_vm_events(PGDEMOTE_DIRECT, nr_succeeded);
> > +
> >       return nr_succeeded;
> >  }
> >
> > diff -puN mm/vmstat.c~mm-vmscan-add-page-demotion-counter mm/vmstat.c
> > --- a/mm/vmstat.c~mm-vmscan-add-page-demotion-counter 2020-10-07 09:15:32.175642439 -0700
> > +++ b/mm/vmstat.c     2020-10-07 09:15:32.181642439 -0700
> > @@ -1244,6 +1244,8 @@ const char * const vmstat_text[] = {
> >       "pgreuse",
> >       "pgsteal_kswapd",
> >       "pgsteal_direct",
> > +     "pgdemote_kswapd",
> > +     "pgdemote_direct",
> >       "pgscan_kswapd",
> >       "pgscan_direct",
> >       "pgscan_direct_throttle",
> > _
>
> Best Regards,
> Huang, Ying
>