Re: [PATCH RFC 3/4] mm/vmstat: rename pgdemote_* to pgdemote_dst_* and add pgdemote_src_*

["Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com>]

On 02/11/2023 13:45, Huang, Ying wrote:
> 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?

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.


>>>   	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@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 */