linux-kernel - Re: [PATCH RFC 3/4] mm/vmstat: rename pgdemote_* to pgdemote_dst_* and add pgdemote_src

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Message-ID: <875y2k1w3t.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Thu, 02 Nov 2023 14:56:54 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yasunori Gotou (Fujitsu)" <y-goto@...itsu.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 3/4] mm/vmstat: rename pgdemote_* to pgdemote_dst_*
 and add pgdemote_src_*

"Zhijian Li (Fujitsu)" <lizhijian@...itsu.com> writes:

> On 02/11/2023 13:45, Huang, Ying wrote:
>> Li Zhijian <lizhijian@...itsu.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?
>
> I recall our customers have mentioned that they want to know how much the memory is demoted
> to the CXL memory device in a specific period.

This doesn't sound like a use case.  Can you elaborate it?  What can
only be tuned with the help of the added stats?

--
Best Regards,
Huang, Ying

>
>>>>   	mod_node_page_state(NODE_DATA(target_nid),
>>>> -		    PGDEMOTE_KSWAPD + reclaimer_offset(), nr_succeeded);
>>>> +		    PGDEMOTE_DST_KSWAPD + reclaimer_offset(), nr_succeeded);
>
> But if the *target_nid* is only indicate the preferred node, this accounting maybe not accurate.
>
>
> Thanks
> Zhijian
>
>> 
>> --
>> Best Regards,
>> Huang, Ying
>> 
>>> Signed-off-by: Li Zhijian <lizhijian@...itsu.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 */