linux-kernel - Re: [PATCH v8 4/6] mm: memcg: add per-memcg zswap writeback stat

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Message-ID: <CAJD7tkZeXY0HbBQu_pZr+kDgoPoDR+kQZq4XxYo6ZXfrO2=BKQ@mail.gmail.com>
Date:   Tue, 5 Dec 2023 10:21:52 -0800
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Nhat Pham <nphamcs@...il.com>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        cerasuolodomenico@...il.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 v8 4/6] mm: memcg: add per-memcg zswap writeback stat

On Thu, Nov 30, 2023 at 11:40 AM Nhat Pham <nphamcs@...il.com> 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                    | 4 ++++
>  4 files changed, 7 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,

I think you dismissed Johannes's comment from v7 about ZSWPWB and
"zswpwb" being more consistent with the existing events.

>  #endif
>  #ifdef CONFIG_X86
>                 DIRECT_MAP_LEVEL2_SPLIT,
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 792ca21c5815..21d79249c8b4 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",
>  #endif
>  #ifdef CONFIG_X86
>         "direct_map_level2_splits",
> diff --git a/mm/zswap.c b/mm/zswap.c
> index f323e45cbdc7..49b79393e472 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -760,6 +760,10 @@ 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);
> +
> +       count_vm_event(ZSWP_WB);
>         /*
>          * Writeback started successfully, the page now belongs to the
>          * swapcache. Drop the entry from zswap - unless invalidate already
> --
> 2.34.1