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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Li Zhijian <lizhijian@fujitsu.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        <rafael@kernel.org>, <linux-mm@kvack.org>, <y-goto@fujitsu.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC 2/4] mm/vmstat: Move pgdemote_* to per-node stats
In-Reply-To: <20231102025648.1285477-3-lizhijian@fujitsu.com> (Li Zhijian's
        message of "Thu, 2 Nov 2023 10:56:46 +0800")
References: <20231102025648.1285477-1-lizhijian@fujitsu.com>
        <20231102025648.1285477-3-lizhijian@fujitsu.com>
Date:   Thu, 02 Nov 2023 13:43:04 +0800
Message-ID: <87v8ak1ziv.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Li Zhijian <lizhijian@fujitsu.com> writes:

> This is a prepare to improve the demotion profiling in the later
> patches.
>
> Per-node demotion stats help users to quickly identify which
> node is in hige stree, and take some special operations if needed.
>
> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
> ---
>  include/linux/mmzone.h        | 4 ++++
>  include/linux/vm_event_item.h | 3 ---
>  mm/vmscan.c                   | 3 ++-
>  mm/vmstat.c                   | 6 +++---
>  4 files changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 4106fbc5b4b3..ad0309eea850 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -206,6 +206,10 @@ enum node_stat_item {
>  #ifdef CONFIG_NUMA_BALANCING
>  	PGPROMOTE_SUCCESS,	/* promote successfully */
>  	PGPROMOTE_CANDIDATE,	/* candidate pages to promote */
> +	/* PGDEMOTE_*: pages demoted */
> +	PGDEMOTE_KSWAPD,
> +	PGDEMOTE_DIRECT,
> +	PGDEMOTE_KHUGEPAGED,
>  #endif
>  	NR_VM_NODE_STAT_ITEMS
>  };
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index 8abfa1240040..d1b847502f09 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -41,9 +41,6 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>  		PGSTEAL_KSWAPD,
>  		PGSTEAL_DIRECT,
>  		PGSTEAL_KHUGEPAGED,
> -		PGDEMOTE_KSWAPD,
> -		PGDEMOTE_DIRECT,
> -		PGDEMOTE_KHUGEPAGED,
>  		PGSCAN_KSWAPD,
>  		PGSCAN_DIRECT,
>  		PGSCAN_KHUGEPAGED,
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 6f13394b112e..2f1fb4ec3235 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1678,7 +1678,8 @@ static unsigned int demote_folio_list(struct list_head *demote_folios,
>  		      (unsigned long)&mtc, MIGRATE_ASYNC, MR_DEMOTION,
>  		      &nr_succeeded);
>  
> -	__count_vm_events(PGDEMOTE_KSWAPD + reclaimer_offset(), nr_succeeded);
> +	mod_node_page_state(NODE_DATA(target_nid),
> +		    PGDEMOTE_KSWAPD + reclaimer_offset(), nr_succeeded);

Think again.  It seems that it's better to count demotion event for the
source node.  Because demotion comes from the memory pressure of the
source node.  The target node isn't so important.  Do you agree?

--
Best Regards,
Huang, Ying

>  
>  	return nr_succeeded;
>  }
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 00e81e99c6ee..f141c48c39e4 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1244,6 +1244,9 @@ const char * const vmstat_text[] = {
>  #ifdef CONFIG_NUMA_BALANCING
>  	"pgpromote_success",
>  	"pgpromote_candidate",
> +	"pgdemote_kswapd",
> +	"pgdemote_direct",
> +	"pgdemote_khugepaged",
>  #endif
>  
>  	/* enum writeback_stat_item counters */
> @@ -1275,9 +1278,6 @@ const char * const vmstat_text[] = {
>  	"pgsteal_kswapd",
>  	"pgsteal_direct",
>  	"pgsteal_khugepaged",
> -	"pgdemote_kswapd",
> -	"pgdemote_direct",
> -	"pgdemote_khugepaged",
>  	"pgscan_kswapd",
>  	"pgscan_direct",
>  	"pgscan_khugepaged",