linux-kernel - Re: [PATCH v7 4/6] mm: memcg: add per-memcg zswap writeback stat

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Date:   Wed, 29 Nov 2023 17:26:35 -0800
From:   Nhat Pham <nphamcs@...il.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     akpm@...ux-foundation.org, cerasuolodomenico@...il.com,
        yosryahmed@...gle.com, sjenning@...hat.com, ddstreet@...e.org,
        vitaly.wool@...sulko.com, mhocko@...nel.org,
        roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, chrisl@...nel.org, linux-mm@...ck.org,
        kernel-team@...a.com, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org, shuah@...nel.org
Subject: Re: [PATCH v7 4/6] mm: memcg: add per-memcg zswap writeback stat

On Wed, Nov 29, 2023 at 7:25 AM Johannes Weiner <hannes@...xchg.org> wrote:
>
> On Mon, Nov 27, 2023 at 03:45:58PM -0800, Nhat Pham wrote:
> > From: Domenico Cerasuolo <cerasuolodomenico@...il.com>
> >
> > Since zswap now writes back pages from memcg-specific LRUs, we now need a
> > new stat to show writebacks count for each memcg.
> >
> > Suggested-by: Nhat Pham <nphamcs@...il.com>
> > Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@...il.com>
> > Signed-off-by: Nhat Pham <nphamcs@...il.com>
> > ---
> >  include/linux/vm_event_item.h | 1 +
> >  mm/memcontrol.c               | 1 +
> >  mm/vmstat.c                   | 1 +
> >  mm/zswap.c                    | 3 +++
> >  4 files changed, 6 insertions(+)
> >
> > diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> > index d1b847502f09..f4569ad98edf 100644
> > --- a/include/linux/vm_event_item.h
> > +++ b/include/linux/vm_event_item.h
> > @@ -142,6 +142,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> >  #ifdef CONFIG_ZSWAP
> >               ZSWPIN,
> >               ZSWPOUT,
> > +             ZSWP_WB,
> >  #endif
> >  #ifdef CONFIG_X86
> >               DIRECT_MAP_LEVEL2_SPLIT,
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 8c0f3f971179..f88c8fd03689 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -703,6 +703,7 @@ static const unsigned int memcg_vm_event_stat[] = {
> >  #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
> >       ZSWPIN,
> >       ZSWPOUT,
> > +     ZSWP_WB,
> >  #endif
> >  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >       THP_FAULT_ALLOC,
> > diff --git a/mm/vmstat.c b/mm/vmstat.c
> > index afa5a38fcc9c..2249f85e4a87 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -1401,6 +1401,7 @@ const char * const vmstat_text[] = {
> >  #ifdef CONFIG_ZSWAP
> >       "zswpin",
> >       "zswpout",
> > +     "zswp_wb",
>
> ZSWPWB and "zswpwb" would match the existing naming scheme a bit
> better.
>
> >  #endif
> >  #ifdef CONFIG_X86
> >       "direct_map_level2_splits",
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index 5e397fc1f375..6a761753f979 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -754,6 +754,9 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
> >       }
> >       zswap_written_back_pages++;
> >
> > +     if (entry->objcg)
> > +             count_objcg_event(entry->objcg, ZSWP_WB);
> > +
>
> You need to call count_vm_event() as well, otherwise the /proc/vmstat
> counter will stay zero.

Ahh I didn't check that. I only looked at the cgroup's memory.stat
counter. I'll fix this for v8!