linux-kernel - Re: [PATCH v4 05/22] mm/slab: make caches with sheaves mergeable

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Message-ID: <iumqtb6shmu7q2dgd4pdcl5n52qhawdjv4p3h26moqnxfrq7q3@54lzpzd767yp>
Date: Tue, 27 Jan 2026 11:23:26 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Harry Yoo <harry.yoo@...cle.com>, Petr Tesarik <ptesarik@...e.com>,
        Christoph Lameter <cl@...two.org>,
        David Rientjes <rientjes@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>, Hao Li <hao.li@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Alexei Starovoitov <ast@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
        bpf@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH v4 05/22] mm/slab: make caches with sheaves mergeable

* Vlastimil Babka <vbabka@...e.cz> [260123 01:53]:
> Before enabling sheaves for all caches (with automatically determined
> capacity), their enablement should no longer prevent merging of caches.
> Limit this merge prevention only to caches that were created with a
> specific sheaf capacity, by adding the SLAB_NO_MERGE flag to them.
> 
> Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

> ---
>  mm/slab_common.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index ee245a880603..5c15a4ce5743 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -162,9 +162,6 @@ int slab_unmergeable(struct kmem_cache *s)
>  		return 1;
>  #endif
>  
> -	if (s->cpu_sheaves)
> -		return 1;
> -
>  	/*
>  	 * We may have set a slab to be unmergeable during bootstrap.
>  	 */
> @@ -189,9 +186,6 @@ static struct kmem_cache *find_mergeable(unsigned int size, slab_flags_t flags,
>  	if (IS_ENABLED(CONFIG_HARDENED_USERCOPY) && args->usersize)
>  		return NULL;
>  
> -	if (args->sheaf_capacity)
> -		return NULL;
> -
>  	flags = kmem_cache_flags(flags, name);
>  
>  	if (flags & SLAB_NEVER_MERGE)
> @@ -336,6 +330,13 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
>  	flags &= ~SLAB_DEBUG_FLAGS;
>  #endif
>  
> +	/*
> +	 * Caches with specific capacity are special enough. It's simpler to
> +	 * make them unmergeable.
> +	 */
> +	if (args->sheaf_capacity)
> +		flags |= SLAB_NO_MERGE;
> +
>  	mutex_lock(&slab_mutex);
>  
>  	err = kmem_cache_sanity_check(name, object_size);
> 
> -- 
> 2.52.0
> 
>