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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 3/4] mm/vmstat: rename pgdemote_* to pgdemote_dst_*
 and add pgdemote_src_*
In-Reply-To: <20231102025648.1285477-4-lizhijian@fujitsu.com> (Li Zhijian's
        message of "Thu, 2 Nov 2023 10:56:47 +0800")
References: <20231102025648.1285477-1-lizhijian@fujitsu.com>
        <20231102025648.1285477-4-lizhijian@fujitsu.com>
Date:   Thu, 02 Nov 2023 13:45:10 +0800
Message-ID: <87r0l81zfd.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Li Zhijian <lizhijian@fujitsu.com> writes:

> pgdemote_src_*: pages demoted from this node.
> pgdemote_dst_*: pages demoted to this node.
>
> So that we are able to know their demotion per-node stats by checking this.
>
> In the environment, node0 and node1 are DRAM, node3 is PMEM.
>
> Global stats:
> $ grep -E 'demote' /proc/vmstat
> pgdemote_src_kswapd 130155
> pgdemote_src_direct 113497
> pgdemote_src_khugepaged 0
> pgdemote_dst_kswapd 130155
> pgdemote_dst_direct 113497
> pgdemote_dst_khugepaged 0
>
> Per-node stats:
> $ grep demote /sys/devices/system/node/node0/vmstat
> pgdemote_src_kswapd 68454
> pgdemote_src_direct 83431
> pgdemote_src_khugepaged 0
> pgdemote_dst_kswapd 0
> pgdemote_dst_direct 0
> pgdemote_dst_khugepaged 0
>
> $ grep demote /sys/devices/system/node/node1/vmstat
> pgdemote_src_kswapd 185834
> pgdemote_src_direct 30066
> pgdemote_src_khugepaged 0
> pgdemote_dst_kswapd 0
> pgdemote_dst_direct 0
> pgdemote_dst_khugepaged 0
>
> $ grep demote /sys/devices/system/node/node3/vmstat
> pgdemote_src_kswapd 0
> pgdemote_src_direct 0
> pgdemote_src_khugepaged 0
> pgdemote_dst_kswapd 254288
> pgdemote_dst_direct 113497
> pgdemote_dst_khugepaged 0
>
> From above stats, we know node3 is the demotion destination which one
> the node0 and node1 will demote to.

Why do we need these information?  Do you have some use case?

--
Best Regards,
Huang, Ying

> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
> ---
> RFC: their names are open to discussion, maybe pgdemote_from/to_*
> Another defect of this patch is that, SUM(pgdemote_src_*) is always same
> as SUM(pgdemote_dst_*) in the global stats, shall we hide one of them.
> ---
>  include/linux/mmzone.h |  9 ++++++---
>  mm/vmscan.c            | 13 ++++++++++---
>  mm/vmstat.c            |  9 ++++++---
>  3 files changed, 22 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index ad0309eea850..a6140d894bec 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -207,9 +207,12 @@ enum node_stat_item {
>  	PGPROMOTE_SUCCESS,	/* promote successfully */
>  	PGPROMOTE_CANDIDATE,	/* candidate pages to promote */
>  	/* PGDEMOTE_*: pages demoted */
> -	PGDEMOTE_KSWAPD,
> -	PGDEMOTE_DIRECT,
> -	PGDEMOTE_KHUGEPAGED,
> +	PGDEMOTE_SRC_KSWAPD,
> +	PGDEMOTE_SRC_DIRECT,
> +	PGDEMOTE_SRC_KHUGEPAGED,
> +	PGDEMOTE_DST_KSWAPD,
> +	PGDEMOTE_DST_DIRECT,
> +	PGDEMOTE_DST_KHUGEPAGED,
>  #endif
>  	NR_VM_NODE_STAT_ITEMS
>  };
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2f1fb4ec3235..55d2287d7150 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1111,13 +1111,18 @@ void drop_slab(void)
>  static int reclaimer_offset(void)
>  {
>  	BUILD_BUG_ON(PGSTEAL_DIRECT - PGSTEAL_KSWAPD !=
> -			PGDEMOTE_DIRECT - PGDEMOTE_KSWAPD);
> +			PGDEMOTE_SRC_DIRECT - PGDEMOTE_SRC_KSWAPD);
>  	BUILD_BUG_ON(PGSTEAL_DIRECT - PGSTEAL_KSWAPD !=
>  			PGSCAN_DIRECT - PGSCAN_KSWAPD);
>  	BUILD_BUG_ON(PGSTEAL_KHUGEPAGED - PGSTEAL_KSWAPD !=
> -			PGDEMOTE_KHUGEPAGED - PGDEMOTE_KSWAPD);
> +			PGDEMOTE_SRC_KHUGEPAGED - PGDEMOTE_SRC_KSWAPD);
>  	BUILD_BUG_ON(PGSTEAL_KHUGEPAGED - PGSTEAL_KSWAPD !=
>  			PGSCAN_KHUGEPAGED - PGSCAN_KSWAPD);
> +	BUILD_BUG_ON(PGDEMOTE_SRC_DIRECT - PGDEMOTE_SRC_KSWAPD !=
> +			PGDEMOTE_DST_DIRECT - PGDEMOTE_DST_KSWAPD);
> +	BUILD_BUG_ON(PGDEMOTE_SRC_KHUGEPAGED - PGDEMOTE_SRC_KSWAPD !=
> +			PGDEMOTE_DST_KHUGEPAGED - PGDEMOTE_DST_KSWAPD);
> +
>  
>  	if (current_is_kswapd())
>  		return 0;
> @@ -1678,8 +1683,10 @@ static unsigned int demote_folio_list(struct list_head *demote_folios,
>  		      (unsigned long)&mtc, MIGRATE_ASYNC, MR_DEMOTION,
>  		      &nr_succeeded);
>  
> +	mod_node_page_state(pgdat,
> +		    PGDEMOTE_SRC_KSWAPD + reclaimer_offset(), nr_succeeded);
>  	mod_node_page_state(NODE_DATA(target_nid),
> -		    PGDEMOTE_KSWAPD + reclaimer_offset(), nr_succeeded);
> +		    PGDEMOTE_DST_KSWAPD + reclaimer_offset(), nr_succeeded);
>  
>  	return nr_succeeded;
>  }
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index f141c48c39e4..63f106a5e008 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1244,9 +1244,12 @@ const char * const vmstat_text[] = {
>  #ifdef CONFIG_NUMA_BALANCING
>  	"pgpromote_success",
>  	"pgpromote_candidate",
> -	"pgdemote_kswapd",
> -	"pgdemote_direct",
> -	"pgdemote_khugepaged",
> +	"pgdemote_src_kswapd",
> +	"pgdemote_src_direct",
> +	"pgdemote_src_khugepaged",
> +	"pgdemote_dst_kswapd",
> +	"pgdemote_dst_direct",
> +	"pgdemote_dst_khugepaged",
>  #endif
>  
>  	/* enum writeback_stat_item counters */