Re: [Patch v2 2/2] mm/page_alloc: not necessary to multiply MAX_NODE_LOAD

[David Hildenbrand <david@redhat.com>]

On 11.04.22 12:52, Vlastimil Babka wrote:
> On 4/9/22 01:07, Wei Yang wrote:
>> On Fri, Apr 08, 2022 at 10:09:48AM +0200, David Hildenbrand wrote:
>>> On 08.04.22 04:59, Wei Yang wrote:
>>>> Since we just increase a constance of 1 to node penalty, it is not
>>>> necessary to multiply MAX_NODE_LOAD for preference.
>>>>
>>>> This patch also remove the definition.
>>>>
>>>> [vbabka@suse.cz: suggests]
>>>>
>>>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>>>> CC: Vlastimil Babka <vbabka@suse.cz>
>>>> CC: David Hildenbrand <david@redhat.com>
>>>> CC: Oscar Salvador <osalvador@suse.de>
>>>> ---
>>>>  mm/page_alloc.c | 3 +--
>>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>>
>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>> index 86b6573fbeb5..ca6a127bbc26 100644
>>>> --- a/mm/page_alloc.c
>>>> +++ b/mm/page_alloc.c
>>>> @@ -6170,7 +6170,6 @@ int numa_zonelist_order_handler(struct ctl_table *table, int write,
>>>>  }
>>>>  
>>>>  
>>>> -#define MAX_NODE_LOAD (nr_online_nodes)
>>>>  static int node_load[MAX_NUMNODES];
>>>>  
>>>>  /**
>>>> @@ -6217,7 +6216,7 @@ int find_next_best_node(int node, nodemask_t *used_node_mask)
>>>>  			val += PENALTY_FOR_NODE_WITH_CPUS;
>>>>  
>>>>  		/* Slight preference for less loaded node */
>>>> -		val *= (MAX_NODE_LOAD*MAX_NUMNODES);
>>>> +		val *= MAX_NUMNODES;
>>>>  		val += node_load[n];
>>>>  
>>>>  		if (val < min_val) {
>>>
>>> I feel like this should be squashed into the previous patch. It has the
>>> same effect of making this code independent of nr_online_nodes. And I
>>> had to scratch my head a couple of times in patch #1 why the change in
>>> patch #1 is fine with thus remaining in place.
>>>
>>>
>>> Having that said, I consider this code highly unnecessary
>>> over-complicated at first sight. Removing some of the magic most
>>> certainly is very welcome.
>>>
>>> This semantics of the global variable node_load[] remains mostly
>>> mysterious for me.
> 
> Looks like after this patch(es), it would be "how many times was this node
> picked as the first fallback out of nodes with the same distance"?

Yeah, that makes sense. I'd appreciate if we'd just stop using a global
variable here and pass it as a parameter. But that's obviously an
independent cleanup.


-- 
Thanks,

David / dhildenb