linux-kernel - Re: [RFC PATCH v3 2/7] slub: Prepare __slab_free() for unfrozen partial slab out of node partial list

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Date:   Sat, 28 Oct 2023 09:35:55 +0800
From:   Chengming Zhou <chengming.zhou@...ux.dev>
To:     Vlastimil Babka <vbabka@...e.cz>, cl@...ux.com, penberg@...nel.org
Cc:     rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, roman.gushchin@...ux.dev,
        42.hyeyoo@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: Re: [RFC PATCH v3 2/7] slub: Prepare __slab_free() for unfrozen
 partial slab out of node partial list

On 2023/10/27 23:18, Vlastimil Babka wrote:
> On 10/24/23 11:33, chengming.zhou@...ux.dev wrote:
>> From: Chengming Zhou <zhouchengming@...edance.com>
>>
>> Now the partial slub will be frozen when taken out of node partial list,
> 
> 	  partially empty slab
> 
>> so the __slab_free() will know from "was_frozen" that the partial slab
>> is not on node partial list and is used by one kmem_cache_cpu.
> 
> 				... is a cpu or cpu partial slab of some cpu.
> 
>> But we will change this, make partial slabs leave the node partial list
>> with unfrozen state, so we need to change __slab_free() to use the new
>> slab_test_node_partial() we just introduced.
>>
>> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
>> ---
>>  mm/slub.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 3fad4edca34b..f568a32d7332 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -3610,6 +3610,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>>  	unsigned long counters;
>>  	struct kmem_cache_node *n = NULL;
>>  	unsigned long flags;
>> +	bool on_node_partial;
>>  
>>  	stat(s, FREE_SLOWPATH);
>>  
>> @@ -3657,6 +3658,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>>  				 */
>>  				spin_lock_irqsave(&n->list_lock, flags);
>>  
>> +				on_node_partial = slab_test_node_partial(slab);
>>  			}
>>  		}
>>  
>> @@ -3685,6 +3687,15 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>>  		return;
>>  	}
>>  
>> +	/*
>> +	 * This slab was partial but not on the per-node partial list,
> 
> This slab was partially empty ...
> 
> Otherwise LGTM!

Ok, will fix.

Thanks!

> 
>> +	 * in which case we shouldn't manipulate its list, just return.
>> +	 */
>> +	if (prior && !on_node_partial) {
>> +		spin_unlock_irqrestore(&n->list_lock, flags);
>> +		return;
>> +	}
>> +
>>  	if (unlikely(!new.inuse && n->nr_partial >= s->min_partial))
>>  		goto slab_empty;
>>  
>