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

From: "Huang\, Ying" <ying.huang@intel.com>
To: Yang Shi <shy828301@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	 Linux MM <linux-mm@kvack.org>,
	 Yang Shi <yang.shi@linux.alibaba.com>,
	 David Rientjes <rientjes@google.com>,
	 Dan Williams <dan.j.williams@intel.com>,
	 David Hildenbrand <david@redhat.com>
Subject: Re: [RFC][PATCH 6/9] mm/vmscan: add page demotion counter
Date: Wed, 28 Oct 2020 09:25:35 +0800	[thread overview]
Message-ID: <87ft5zywds.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <CAHbLzkpFTVhBhrj715ixu_bYrbpOZwLn3Y3=+miKs9hCCiOW7g@mail.gmail.com> (Yang Shi's message of "Tue, 27 Oct 2020 09:41:27 -0700")

Yang Shi <shy828301@gmail.com> writes:

> On Mon, Oct 19, 2020 at 12:38 AM Huang, Ying <ying.huang@intel.com> wrote:
>>
>> Dave Hansen <dave.hansen@linux.intel.com> writes:
>>
>> > From: Yang Shi <yang.shi@linux.alibaba.com>
>> >
>> > 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@linux.alibaba.com>
>> > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
>> > Cc: David Rientjes <rientjes@google.com>
>> > Cc: Huang Ying <ying.huang@intel.com>
>> > Cc: Dan Williams <dan.j.williams@intel.com>
>> > Cc: David Hildenbrand <david@redhat.com>
>> > ---
>> >
>> >  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.

Personally, I prefer to collect nr_demoted in struct reclaim_stat and
call counting functions in shrink_inactive_list() as other reclaiming
statistics.

Best Regards,
Huang, Ying

>>
>> >       } 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
>>