linux-kernel - Re: [PATCH v2 4/5] mm/slub: limit number of node partial slabs only in cache creation

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Message-ID: <e0e983ae-fce7-f814-131e-ac5386550bc3@suse.cz>
Date:   Fri, 4 Mar 2022 19:33:10 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org
Cc:     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>,
        Marco Elver <elver@...gle.com>,
        Matthew WilCox <willy@...radead.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/5] mm/slub: limit number of node partial slabs only
 in cache creation

On 3/4/22 07:34, Hyeonggon Yoo wrote:
> SLUB sets number of minimum partial slabs for node (min_partial)
> using set_min_partial(). SLUB holds at least min_partial slabs even if
> they're empty to avoid excessive use of page allocator.
> 
> set_min_partial() limits value of min_partial limits value of
> min_partial MIN_PARTIAL and MAX_PARTIAL. As set_min_partial() can be
> called by min_partial_store() too, Only limit value of min_partial
> in kmem_cache_open() so that it can be changed to value that a user wants.
> 
> [ rientjes@...gle.com: Fold set_min_partial() into its callers ]
> 
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/slub.c | 14 +++-----------
>  1 file changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 6f0ebadd8f30..f9ae983a3dc6 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3981,15 +3981,6 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
>  	return 1;
>  }
>  
> -static void set_min_partial(struct kmem_cache *s, unsigned long min)
> -{
> -	if (min < MIN_PARTIAL)
> -		min = MIN_PARTIAL;
> -	else if (min > MAX_PARTIAL)
> -		min = MAX_PARTIAL;
> -	s->min_partial = min;
> -}
> -
>  static void set_cpu_partial(struct kmem_cache *s)
>  {
>  #ifdef CONFIG_SLUB_CPU_PARTIAL
> @@ -4196,7 +4187,8 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
>  	 * The larger the object size is, the more slabs we want on the partial
>  	 * list to avoid pounding the page allocator excessively.
>  	 */
> -	set_min_partial(s, ilog2(s->size) / 2);
> +	s->min_partial = min_t(unsigned long, MAX_PARTIAL, ilog2(s->size) / 2);
> +	s->min_partial = max_t(unsigned long, MIN_PARTIAL, s->min_partial);
>  
>  	set_cpu_partial(s);
>  
> @@ -5361,7 +5353,7 @@ static ssize_t min_partial_store(struct kmem_cache *s, const char *buf,
>  	if (err)
>  		return err;
>  
> -	set_min_partial(s, min);
> +	s->min_partial = min;
>  	return length;
>  }
>  SLAB_ATTR(min_partial);