linux-kernel - Re: [PATCH v3 07/35] mm/slab: introduce SLAB_NO_OBJ_EXT to avoid obj

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Date: Thu, 15 Feb 2024 22:31:06 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
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Subject: Re: [PATCH v3 07/35] mm/slab: introduce SLAB_NO_OBJ_EXT to avoid
 obj_ext creation

On 2/12/24 22:38, Suren Baghdasaryan wrote:
> Slab extension objects can't be allocated before slab infrastructure is
> initialized. Some caches, like kmem_cache and kmem_cache_node, are created
> before slab infrastructure is initialized. Objects from these caches can't
> have extension objects. Introduce SLAB_NO_OBJ_EXT slab flag to mark these
> caches and avoid creating extensions for objects allocated from these
> slabs.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
>  include/linux/slab.h | 7 +++++++
>  mm/slub.c            | 5 +++--
>  2 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index b5f5ee8308d0..3ac2fc830f0f 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -164,6 +164,13 @@
>  #endif
>  #define SLAB_TEMPORARY		SLAB_RECLAIM_ACCOUNT	/* Objects are short-lived */
>  
> +#ifdef CONFIG_SLAB_OBJ_EXT
> +/* Slab created using create_boot_cache */
> +#define SLAB_NO_OBJ_EXT         ((slab_flags_t __force)0x20000000U)

There's
   #define SLAB_SKIP_KFENCE        ((slab_flags_t __force)0x20000000U)
already, so need some other one?

> +#else
> +#define SLAB_NO_OBJ_EXT         0
> +#endif
> +
>  /*
>   * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
>   *
> diff --git a/mm/slub.c b/mm/slub.c
> index 1eb1050814aa..9fd96238ed39 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5650,7 +5650,8 @@ void __init kmem_cache_init(void)
>  		node_set(node, slab_nodes);
>  
>  	create_boot_cache(kmem_cache_node, "kmem_cache_node",
> -		sizeof(struct kmem_cache_node), SLAB_HWCACHE_ALIGN, 0, 0);
> +			sizeof(struct kmem_cache_node),
> +			SLAB_HWCACHE_ALIGN | SLAB_NO_OBJ_EXT, 0, 0);
>  
>  	hotplug_memory_notifier(slab_memory_callback, SLAB_CALLBACK_PRI);
>  
> @@ -5660,7 +5661,7 @@ void __init kmem_cache_init(void)
>  	create_boot_cache(kmem_cache, "kmem_cache",
>  			offsetof(struct kmem_cache, node) +
>  				nr_node_ids * sizeof(struct kmem_cache_node *),
> -		       SLAB_HWCACHE_ALIGN, 0, 0);
> +			SLAB_HWCACHE_ALIGN | SLAB_NO_OBJ_EXT, 0, 0);
>  
>  	kmem_cache = bootstrap(&boot_kmem_cache);
>  	kmem_cache_node = bootstrap(&boot_kmem_cache_node);