Re: [PATCH RFC hotfixes 1/2] mm/slab: decouple SLAB_NO_SHEAVES from SLAB_NO_OBJ_EXT

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 7/2/26 06:09, Harry Yoo (Oracle) wrote:
> Bootstrap caches are created with SLAB_NO_OBJ_EXT to disallow sheaves
> and obj_exts.
> 
> To allow disabling obj_exts while allowing sheaves, decouple
> SLAB_NO_SHEAVES from SLAB_NO_OBJ_EXT. Bootstrap caches now have both
> SLAB_NO_SHEAVES and SLAB_NO_OBJ_EXT.
> 
> No functional change intended.
> 
> Cc: stable@vger.kernel.org
> Fixes: e47c897a2949 ("slab: add sheaves to most caches")
> Signed-off-by: Harry Yoo (Oracle) <harry@kernel.org>

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

> ---
>  include/linux/slab.h | 13 +++++++++++--
>  mm/slub.c            | 10 ++++++----
>  2 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 51f03f18c9a7..08d7b6c9c4d6 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -58,10 +58,13 @@ enum _slab_flag_bits {
>  #endif
>  	_SLAB_OBJECT_POISON,
>  	_SLAB_CMPXCHG_DOUBLE,
> +#ifdef CONFIG_SLAB_OBJ_EXT
>  	_SLAB_NO_OBJ_EXT,
> -#if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT)
> +#ifdef CONFIG_64BIT
>  	_SLAB_OBJ_EXT_IN_OBJ,
>  #endif
> +#endif
> +	_SLAB_NO_SHEAVES,
>  	_SLAB_FLAGS_LAST_BIT
>  };
>  
> @@ -239,8 +242,14 @@ enum _slab_flag_bits {
>  #endif
>  #define SLAB_TEMPORARY		SLAB_RECLAIM_ACCOUNT	/* Objects are short-lived */
>  
> -/* Slab created using create_boot_cache */
> +/* Slab caches without obj_exts array */
> +#ifdef CONFIG_SLAB_OBJ_EXT
>  #define SLAB_NO_OBJ_EXT		__SLAB_FLAG_BIT(_SLAB_NO_OBJ_EXT)
> +#else
> +#define SLAB_NO_OBJ_EXT		__SLAB_FLAG_UNUSED
> +#endif
> +
> +#define SLAB_NO_SHEAVES		__SLAB_FLAG_BIT(_SLAB_NO_SHEAVES)
>  
>  #if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT)
>  #define SLAB_OBJ_EXT_IN_OBJ	__SLAB_FLAG_BIT(_SLAB_OBJ_EXT_IN_OBJ)
> diff --git a/mm/slub.c b/mm/slub.c
> index 9f754cf1c187..efc85053ae84 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -7777,12 +7777,12 @@ static unsigned int calculate_sheaf_capacity(struct kmem_cache *s,
>  		return 0;
>  
>  	/*
> -	 * Bootstrap caches can't have sheaves for now (SLAB_NO_OBJ_EXT).
> +	 * Bootstrap caches can't have sheaves for now (SLAB_NO_SHEAVES).
>  	 * SLAB_NOLEAKTRACE caches (e.g., kmemleak's object_cache) must not
>  	 * have sheaves to avoid recursion when sheaf allocation triggers
>  	 * kmemleak tracking.
>  	 */
> -	if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE))
> +	if (s->flags & (SLAB_NO_SHEAVES | SLAB_NOLEAKTRACE))
>  		return 0;
>  
>  	/*
> @@ -8559,7 +8559,8 @@ void __init kmem_cache_init(void)
>  
>  	create_boot_cache(kmem_cache_node, "kmem_cache_node",
>  			sizeof(struct kmem_cache_node),
> -			SLAB_HWCACHE_ALIGN | SLAB_NO_OBJ_EXT, 0, 0);
> +			SLAB_HWCACHE_ALIGN | SLAB_NO_SHEAVES | SLAB_NO_OBJ_EXT,
> +			0, 0);
>  
>  	hotplug_node_notifier(slab_memory_callback, SLAB_CALLBACK_PRI);
>  
> @@ -8569,7 +8570,8 @@ void __init kmem_cache_init(void)
>  	create_boot_cache(kmem_cache, "kmem_cache",
>  			offsetof(struct kmem_cache, per_node) +
>  				nr_node_ids * sizeof(struct kmem_cache_per_node_ptrs),
> -			SLAB_HWCACHE_ALIGN | SLAB_NO_OBJ_EXT, 0, 0);
> +			SLAB_HWCACHE_ALIGN | SLAB_NO_SHEAVES | SLAB_NO_OBJ_EXT,
> +			0, 0);
>  
>  	kmem_cache = bootstrap(&boot_kmem_cache);
>  	kmem_cache_node = bootstrap(&boot_kmem_cache_node);
>