Re: [PATCH v3 2/2] mm, slab: simplify returning slab in __refill_objects_node()

[Vlastimil Babka (SUSE)]

On 5/25/26 08:47, Hao Li wrote:
> On Fri, May 22, 2026 at 04:23:21PM +0200, Vlastimil Babka (SUSE) wrote:
>> When we return slabs to the partial list because we didn't fully refill
>> from them, we observe the min_partial limit when the returned slab is
>> empty, and discard it when over the limit. But it's unlikely for the
>> limit to be reached while we were refilling, and the worst outcome is to
>> have temporarily more free slabs on the list than necessary.
> 
> Just wondering if the empty slabs temporarily exceed the limit and then some
> objects get allocated from them, would this lead to more fragmented slabs in
> the node partial list?

I think since we're adding the slabs to tail and refill from head, it
shouldn't happen that easily. Fragmenting is possible in general due to bad
luck, I doubt this change could make it noticeably worse.

>> So just
>> drop that code and simplify the function.
>> 
>> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
>> ---
>>  mm/slub.c | 10 ----------
>>  1 file changed, 10 deletions(-)
>> 
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 5816fcfc7a90..074d57c0390b 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -7196,21 +7196,11 @@ __refill_objects_node(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int mi
>>  
>>  		list_for_each_entry_safe(slab, slab2, &pc.slabs, slab_list) {
>>  
>> -			if (unlikely(!slab->inuse && n->nr_partial >= s->min_partial))
>> -				continue;
>> -
>>  			list_del(&slab->slab_list);
>>  			add_partial(n, slab, ADD_TO_TAIL);
>>  		}
>>  
>>  		spin_unlock_irqrestore(&n->list_lock, flags);
>> -
>> -		/* any slabs left are completely free and for discard */
>> -		list_for_each_entry_safe(slab, slab2, &pc.slabs, slab_list) {
>> -
>> -			list_del(&slab->slab_list);
>> -			discard_slab(s, slab);
>> -		}
>>  	}
>>  
>>  	return refilled;
>> 
>> -- 
>> 2.54.0
>> 
>