net: skbuff: remove special handling for SLOB

Commit c9929f0e ("mm/slob: remove CONFIG_SLOB") removes CONFIG_SLOB.
Now, we can also remove special handling for socket buffers with the SLOB
allocator. The code with HAVE_SKB_SMALL_HEAD_CACHE=1 is now the default
behavior for all allocators.

Remove an unnecessary distinction between SLOB and SLAB/SLUB allocator
after the SLOB allocator is gone.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230509071207.28942-1-lukas.bulwahn@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/skbuff.c

@@ -92,15 +92,7 @@ static struct kmem_cache *skbuff_fclone_cache __ro_after_init;
 static struct kmem_cache *skbuff_ext_cache __ro_after_init;
 #endif
 
-/* skb_small_head_cache and related code is only supported
- * for CONFIG_SLAB and CONFIG_SLUB.
- * As soon as SLOB is removed from the kernel, we can clean up this.
- */
-#if !defined(CONFIG_SLOB)
-# define HAVE_SKB_SMALL_HEAD_CACHE 1
-#endif
 
-#ifdef HAVE_SKB_SMALL_HEAD_CACHE
 static struct kmem_cache *skb_small_head_cache __ro_after_init;
 
 #define SKB_SMALL_HEAD_SIZE SKB_HEAD_ALIGN(MAX_TCP_HEADER)
@@ -117,7 +109,6 @@ static struct kmem_cache *skb_small_head_cache __ro_after_init;
 
 #define SKB_SMALL_HEAD_HEADROOM						\
 	SKB_WITH_OVERHEAD(SKB_SMALL_HEAD_CACHE_SIZE)
-#endif /* HAVE_SKB_SMALL_HEAD_CACHE */
 
 int sysctl_max_skb_frags __read_mostly = MAX_SKB_FRAGS;
 EXPORT_SYMBOL(sysctl_max_skb_frags);
@@ -562,7 +553,6 @@ static void *kmalloc_reserve(unsigned int *size, gfp_t flags, int node,
 	void *obj;
 
 	obj_size = SKB_HEAD_ALIGN(*size);
-#ifdef HAVE_SKB_SMALL_HEAD_CACHE
 	if (obj_size <= SKB_SMALL_HEAD_CACHE_SIZE &&
 	    !(flags & KMALLOC_NOT_NORMAL_BITS)) {
 		obj = kmem_cache_alloc_node(skb_small_head_cache,
@@ -576,7 +566,6 @@ static void *kmalloc_reserve(unsigned int *size, gfp_t flags, int node,
 		obj = kmem_cache_alloc_node(skb_small_head_cache, flags, node);
 		goto out;
 	}
-#endif
 	*size = obj_size = kmalloc_size_roundup(obj_size);
 	/*
 	 * Try a regular allocation, when that fails and we're not entitled
@@ -898,11 +887,9 @@ static bool skb_pp_recycle(struct sk_buff *skb, void *data, bool napi_safe)
 
 static void skb_kfree_head(void *head, unsigned int end_offset)
 {
-#ifdef HAVE_SKB_SMALL_HEAD_CACHE
 	if (end_offset == SKB_SMALL_HEAD_HEADROOM)
 		kmem_cache_free(skb_small_head_cache, head);
 	else
-#endif
 		kfree(head);
 }
 
@@ -2160,7 +2147,6 @@ int __skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri)
 	if (likely(skb_end_offset(skb) == saved_end_offset))
 		return 0;
 
-#ifdef HAVE_SKB_SMALL_HEAD_CACHE
 	/* We can not change skb->end if the original or new value
 	 * is SKB_SMALL_HEAD_HEADROOM, as it might break skb_kfree_head().
 	 */
@@ -2174,7 +2160,6 @@ int __skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri)
 		WARN_ON_ONCE(1);
 		return 0;
 	}
-#endif
 
 	shinfo = skb_shinfo(skb);
 
@@ -4768,7 +4753,6 @@ void __init skb_init(void)
 						0,
 						SLAB_HWCACHE_ALIGN|SLAB_PANIC,
 						NULL);
-#ifdef HAVE_SKB_SMALL_HEAD_CACHE
 	/* usercopy should only access first SKB_SMALL_HEAD_HEADROOM bytes.
 	 * struct skb_shared_info is located at the end of skb->head,
 	 * and should not be copied to/from user.
@@ -4780,7 +4764,6 @@ void __init skb_init(void)
 						0,
 						SKB_SMALL_HEAD_HEADROOM,
 						NULL);
-#endif
 	skb_extensions_init();
 }