Re: CK1 [03/13] slub: Use a statically allocated kmem_cache boot structure for bootstrap

[Glauber Costa <glommer@parallels.com>]

On 09/27/2012 12:20 AM, Christoph Lameter wrote:
> Simplify bootstrap by statically allocated two kmem_cache structures. These are
> freed after bootup is complete. Allows us to no longer worry about calculations
> of sizes of kmem_cache structures during bootstrap.
> 
> V1->V2: Do not unlock mutexes that are not taken during early boot.
> 
This V1->V2 change makes sense, btw.

> Reviewed-by: Glauber Costa <glommer@parallels.com>
> Signed-off-by: Christoph Lameter <cl@linux.com>
> ---
>  mm/slub.c |   41 +++++++++++------------------------------
>  1 file changed, 11 insertions(+), 30 deletions(-)
> 
> Index: linux/mm/slub.c
> ===================================================================
> --- linux.orig/mm/slub.c	2012-09-19 09:21:14.422971030 -0500
> +++ linux/mm/slub.c	2012-09-19 09:21:18.403053765 -0500
> @@ -3649,9 +3649,6 @@ static void __init kmem_cache_bootstrap_
>  {
>  	int node;
>  
> -	list_add(&s->list, &slab_caches);
> -	s->refcount = -1;
> -
>  	for_each_node_state(node, N_NORMAL_MEMORY) {
>  		struct kmem_cache_node *n = get_node(s, node);
>  		struct page *p;
> @@ -3668,14 +3665,13 @@ static void __init kmem_cache_bootstrap_
>  	}
>  }
>  
> +static __initdata struct kmem_cache boot_kmem_cache,
> +			boot_kmem_cache_node;
> +
>  void __init kmem_cache_init(void)
>  {
>  	int i;
> -	int caches = 0;
> -	struct kmem_cache *temp_kmem_cache;
> -	int order;
> -	struct kmem_cache *temp_kmem_cache_node;
> -	unsigned long kmalloc_size;
> +	int caches = 2;
>  
>  	if (debug_guardpage_minorder())
>  		slub_max_order = 0;
> @@ -3683,53 +3679,32 @@ void __init kmem_cache_init(void)
>  	kmem_size = offsetof(struct kmem_cache, node) +
>  			nr_node_ids * sizeof(struct kmem_cache_node *);
>  
> -	/* Allocate two kmem_caches from the page allocator */
> -	kmalloc_size = ALIGN(kmem_size, cache_line_size());
> -	order = get_order(2 * kmalloc_size);
> -	kmem_cache = (void *)__get_free_pages(GFP_NOWAIT | __GFP_ZERO, order);
> -
> -	/*
> -	 * Must first have the slab cache available for the allocations of the
> -	 * struct kmem_cache_node's. There is special bootstrap code in
> -	 * kmem_cache_open for slab_state == DOWN.
> -	 */
> -	kmem_cache_node = (void *)kmem_cache + kmalloc_size;
> +	kmem_cache_node = &boot_kmem_cache_node;
>  
> -	kmem_cache_node->name = "kmem_cache_node";
> -	kmem_cache_node->size = kmem_cache_node->object_size =
> -		sizeof(struct kmem_cache_node);
> -	kmem_cache_open(kmem_cache_node, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
> +	create_boot_cache(kmem_cache_node, "kmem_cache_node",
> +		sizeof(struct kmem_cache_node), SLAB_HWCACHE_ALIGN);
>  
>  	hotplug_memory_notifier(slab_memory_callback, SLAB_CALLBACK_PRI);
>  
>  	/* Able to allocate the per node structures */
>  	slab_state = PARTIAL;
>  
> -	temp_kmem_cache = kmem_cache;
> -	kmem_cache->name = "kmem_cache";
> -	kmem_cache->size = kmem_cache->object_size = kmem_size;
> -	kmem_cache_open(kmem_cache, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
> +	create_boot_cache(&boot_kmem_cache, "kmem_cache", kmem_size,
> +		       SLAB_HWCACHE_ALIGN);
>  
> -	kmem_cache = kmem_cache_alloc(kmem_cache, GFP_NOWAIT);
> -	memcpy(kmem_cache, temp_kmem_cache, kmem_size);
> +	kmem_cache = kmem_cache_alloc(&boot_kmem_cache, GFP_NOWAIT);
> +	memcpy(kmem_cache, &boot_kmem_cache, kmem_size);
>  
>  	/*
>  	 * Allocate kmem_cache_node properly from the kmem_cache slab.
>  	 * kmem_cache_node is separately allocated so no need to
>  	 * update any list pointers.
>  	 */
> -	temp_kmem_cache_node = kmem_cache_node;
> -
>  	kmem_cache_node = kmem_cache_alloc(kmem_cache, GFP_NOWAIT);
> -	memcpy(kmem_cache_node, temp_kmem_cache_node, kmem_size);
> +	memcpy(kmem_cache_node, &boot_kmem_cache_node, kmem_size);
>  
>  	kmem_cache_bootstrap_fixup(kmem_cache_node);
> -
> -	caches++;
>  	kmem_cache_bootstrap_fixup(kmem_cache);
> -	caches++;
> -	/* Free temporary boot structure */
> -	free_pages((unsigned long)temp_kmem_cache, order);
>  
>  	/* Now we can use the kmem_cache to allocate kmalloc slabs */
>  
> @@ -3930,6 +3905,10 @@ int __kmem_cache_create(struct kmem_cach
>  	if (err)
>  		return err;
>  
> +	/* Mutex is not taken during early boot */
> +	if (slab_state <= UP)
> +		return 0;
> +
>  	mutex_unlock(&slab_mutex);
>  	err = sysfs_slab_add(s);
>  	mutex_lock(&slab_mutex);
> 
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