linux-kernel - Re: [PATCH] mm/slub: Simplify get_partial

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Date: Tue, 12 Mar 2024 14:21:06 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: sxwjean@...com, Christoph Lameter <cl@...ux.com>,
 Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>,
 Joonsoo Kim <iamjoonsoo.kim@....com>,
 Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Xiongwei Song <xiongwei.song@...driver.com>
Subject: Re: [PATCH] mm/slub: Simplify get_partial_node()

On 2024/3/11 21:27, sxwjean@...com wrote:
> From: Xiongwei Song <xiongwei.song@...driver.com>
> 
> Remove the check of !kmem_cache_has_cpu_partial() because it is always
> false, we've known this by calling kmem_cache_debug() before calling
> remove_partial(), so we can remove the check.

This is correct.

> 
> Meanwhile, redo filling cpu partial and add comment to improve the
> readability.
> 
> Signed-off-by: Xiongwei Song <xiongwei.song@...driver.com>
> ---
>  mm/slub.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index a3ab096c38c0..62388f2a0ac7 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2620,19 +2620,21 @@ static struct slab *get_partial_node(struct kmem_cache *s,
>  		if (!partial) {
>  			partial = slab;
>  			stat(s, ALLOC_FROM_PARTIAL);
> -		} else {
> +
> +			/* Fill cpu partial if needed from next iteration, or break */
> +			if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))
> +				continue;
> +			else
> +				break;
> +		}
> +
> +		if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)) {

But this won't work since "s->cpu_partial_slabs" is defined under CONFIG_SLUB_CPU_PARTIAL,
you would get compiler error if building without CONFIG_SLUB_CPU_PARTIAL.

Thanks.

>  			put_cpu_partial(s, slab, 0);
>  			stat(s, CPU_PARTIAL_NODE);
> -			partial_slabs++;
> -		}
> -#ifdef CONFIG_SLUB_CPU_PARTIAL
> -		if (!kmem_cache_has_cpu_partial(s)
> -			|| partial_slabs > s->cpu_partial_slabs / 2)
> -			break;
> -#else
> -		break;
> -#endif
>  
> +			if (++partial_slabs > s->cpu_partial_slabs/2)
> +				break;
> +		}
>  	}
>  	spin_unlock_irqrestore(&n->list_lock, flags);
>  	return partial;