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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Message-ID: <43da5c9a-aeff-1bff-81a8-4611470c2514@suse.cz>
Date:   Fri, 27 Oct 2023 17:18:40 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     chengming.zhou@...ux.dev, 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 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!

> +	 * 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;
>