Re: [PATCH 1/8] mm/migrate.c: skip node check if done in last round

[Wei Yang <richardw.yang@linux.intel.com>]

On Mon, Jan 20, 2020 at 10:36:46AM +0100, Michal Hocko wrote:
>On Sun 19-01-20 11:06:29, Wei Yang wrote:
>> Before move page to target node, we would check if the node id is valid.
>> In case we would try to move pages to the same target node, it is not
>> necessary to do the check each time.
>> 
>> This patch tries to skip the check if the node has been checked.
>> 
>> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> ---
>>  mm/migrate.c | 19 +++++++++++--------
>>  1 file changed, 11 insertions(+), 8 deletions(-)
>> 
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 430fdccc733e..ba7cf4fa43a0 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1612,15 +1612,18 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
>>  			goto out_flush;
>>  		addr = (unsigned long)untagged_addr(p);
>>  
>> -		err = -ENODEV;
>> -		if (node < 0 || node >= MAX_NUMNODES)
>> -			goto out_flush;
>> -		if (!node_state(node, N_MEMORY))
>> -			goto out_flush;
>> +		/* Check node if it is not checked. */
>> +		if (current_node == NUMA_NO_NODE || node != current_node) {
>> +			err = -ENODEV;
>> +			if (node < 0 || node >= MAX_NUMNODES)
>> +				goto out_flush;
>> +			if (!node_state(node, N_MEMORY))
>> +				goto out_flush;
>
>This makes the code harder to read IMHO. The original code checks the
>valid node first and it doesn't conflate that with the node caching
>logic which your change does.
>

I am sorry, would you mind showing me an example about the conflate in my
change? I don't get it.

>>  
>> -		err = -EACCES;
>> -		if (!node_isset(node, task_nodes))
>> -			goto out_flush;
>> +			err = -EACCES;
>> +			if (!node_isset(node, task_nodes))
>> +				goto out_flush;
>> +		}
>>  
>>  		if (current_node == NUMA_NO_NODE) {
>>  			current_node = node;
>> -- 
>> 2.17.1
>
>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
Help you, Help me