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

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Message-ID: <20231129152509.GD135852@cmpxchg.org>
Date:   Wed, 29 Nov 2023 10:25:09 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Nhat Pham <nphamcs@...il.com>
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 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.