Re: [PATCH v3 10/15] mm/slab: kmalloc: pass requests larger than order-1 page to page allocator

[Vlastimil Babka <vbabka@suse.cz>]

On 7/12/22 15:39, Hyeonggon Yoo wrote:
> There is not much benefit for serving large objects in kmalloc().
> Let's pass large requests to page allocator like SLUB for better
> maintenance of common code.
> 
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> v2->v3: 
> 	This patch is basically same but it now depends on
> 	kmalloc_large_node_notrace().
> 
>  include/linux/slab.h | 23 ++++-------------
>  mm/slab.c            | 60 +++++++++++++++++++++++++++++++-------------
>  mm/slab.h            |  3 +++
>  mm/slab_common.c     | 25 ++++++++++++------
>  mm/slub.c            | 19 --------------
>  5 files changed, 68 insertions(+), 62 deletions(-)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index fd2e129fc813..4ee5b2fed164 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -243,27 +243,17 @@ static inline unsigned int arch_slab_minalign(void)
>  
>  #ifdef CONFIG_SLAB
>  /*
> - * The largest kmalloc size supported by the SLAB allocators is
> - * 32 megabyte (2^25) or the maximum allocatable page order if that is
> - * less than 32 MB.
> - *
> - * WARNING: Its not easy to increase this value since the allocators have
> - * to do various tricks to work around compiler limitations in order to
> - * ensure proper constant folding.
> + * SLAB and SLUB directly allocates requests fitting in to an order-1 page
> + * (PAGE_SIZE*2).  Larger requests are passed to the page allocator.
>   */
> -#define KMALLOC_SHIFT_HIGH	((MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
> -				(MAX_ORDER + PAGE_SHIFT - 1) : 25)
> -#define KMALLOC_SHIFT_MAX	KMALLOC_SHIFT_HIGH
> +#define KMALLOC_SHIFT_HIGH	(PAGE_SHIFT + 1)
> +#define KMALLOC_SHIFT_MAX	(MAX_ORDER + PAGE_SHIFT - 1)
>  #ifndef KMALLOC_SHIFT_LOW
>  #define KMALLOC_SHIFT_LOW	5
>  #endif
>  #endif
>  
>  #ifdef CONFIG_SLUB
> -/*
> - * SLUB directly allocates requests fitting in to an order-1 page
> - * (PAGE_SIZE*2).  Larger requests are passed to the page allocator.
> - */
>  #define KMALLOC_SHIFT_HIGH	(PAGE_SHIFT + 1)
>  #define KMALLOC_SHIFT_MAX	(MAX_ORDER + PAGE_SHIFT - 1)
>  #ifndef KMALLOC_SHIFT_LOW
> @@ -415,10 +405,6 @@ static __always_inline unsigned int __kmalloc_index(size_t size,
>  	if (size <= 512 * 1024) return 19;
>  	if (size <= 1024 * 1024) return 20;
>  	if (size <=  2 * 1024 * 1024) return 21;
> -	if (size <=  4 * 1024 * 1024) return 22;
> -	if (size <=  8 * 1024 * 1024) return 23;
> -	if (size <=  16 * 1024 * 1024) return 24;
> -	if (size <=  32 * 1024 * 1024) return 25;
>  
>  	if (!IS_ENABLED(CONFIG_PROFILE_ALL_BRANCHES) && size_is_constant)
>  		BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()");
> @@ -428,6 +414,7 @@ static __always_inline unsigned int __kmalloc_index(size_t size,
>  	/* Will never be reached. Needed because the compiler may complain */
>  	return -1;
>  }
> +static_assert(PAGE_SHIFT <= 20);
>  #define kmalloc_index(s) __kmalloc_index(s, true)
>  #endif /* !CONFIG_SLOB */
>  
> diff --git a/mm/slab.c b/mm/slab.c
> index ab34727d61b2..a2f43425a0ae 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3585,11 +3585,19 @@ __do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller)
>  	struct kmem_cache *cachep;
>  	void *ret;
>  
> -	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))
> -		return NULL;
> +	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) {
> +		ret = kmalloc_large_node_notrace(size, flags, node);
> +
> +		trace_kmalloc_node(caller, ret, NULL, size,
> +				   PAGE_SIZE << get_order(size),
> +				   flags, node);
> +		return ret;
> +	}
> +
>  	cachep = kmalloc_slab(size, flags);
>  	if (unlikely(ZERO_OR_NULL_PTR(cachep)))
>  		return cachep;
> +
>  	ret = kmem_cache_alloc_node_trace(cachep, flags, node, size);
>  	ret = kasan_kmalloc(cachep, ret, size, flags);
>  
> @@ -3664,17 +3672,27 @@ EXPORT_SYMBOL(kmem_cache_free);
>  
>  void kmem_cache_free_bulk(struct kmem_cache *orig_s, size_t size, void **p)
>  {
> -	struct kmem_cache *s;
> -	size_t i;
>  
>  	local_irq_disable();
> -	for (i = 0; i < size; i++) {
> +	for (int i = 0; i < size; i++) {
>  		void *objp = p[i];
> +		struct kmem_cache *s;
>  
> -		if (!orig_s) /* called via kfree_bulk */
> -			s = virt_to_cache(objp);
> -		else
> +		if (!orig_s) {
> +			struct folio *folio = virt_to_folio(objp);
> +
> +			/* called via kfree_bulk */
> +			if (!folio_test_slab(folio)) {
> +				local_irq_enable();
> +				free_large_kmalloc(folio, objp);
> +				local_irq_disable();
> +				continue;
> +			}
> +			s = folio_slab(folio)->slab_cache;
> +		} else {
>  			s = cache_from_obj(orig_s, objp);
> +		}
> +
>  		if (!s)
>  			continue;
>  
> @@ -3703,20 +3721,24 @@ void kfree(const void *objp)
>  {
>  	struct kmem_cache *c;
>  	unsigned long flags;
> +	struct folio *folio;
>  
>  	trace_kfree(_RET_IP_, objp);
>  
>  	if (unlikely(ZERO_OR_NULL_PTR(objp)))
>  		return;
> -	local_irq_save(flags);
> -	kfree_debugcheck(objp);
> -	c = virt_to_cache(objp);
> -	if (!c) {
> -		local_irq_restore(flags);
> +
> +	folio = virt_to_folio(objp);
> +	if (!folio_test_slab(folio)) {
> +		free_large_kmalloc(folio, (void *)objp);
>  		return;
>  	}
> -	debug_check_no_locks_freed(objp, c->object_size);
>  
> +	c = folio_slab(folio)->slab_cache;
> +
> +	local_irq_save(flags);
> +	kfree_debugcheck(objp);
> +	debug_check_no_locks_freed(objp, c->object_size);
>  	debug_check_no_obj_freed(objp, c->object_size);
>  	__cache_free(c, (void *)objp, _RET_IP_);
>  	local_irq_restore(flags);
> @@ -4138,15 +4160,17 @@ void __check_heap_object(const void *ptr, unsigned long n,
>  size_t __ksize(const void *objp)
>  {
>  	struct kmem_cache *c;
> -	size_t size;
> +	struct folio *folio;
>  
>  	BUG_ON(!objp);
>  	if (unlikely(objp == ZERO_SIZE_PTR))
>  		return 0;
>  
> -	c = virt_to_cache(objp);
> -	size = c ? c->object_size : 0;
> +	folio = virt_to_folio(objp);
> +	if (!folio_test_slab(folio))
> +		return folio_size(folio);
>  
> -	return size;
> +	c = folio_slab(folio)->slab_cache;
> +	return c->object_size;
>  }
>  EXPORT_SYMBOL(__ksize);
> diff --git a/mm/slab.h b/mm/slab.h
> index 7cb51ff44f0c..c81c92d421f1 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -669,6 +669,9 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
>  		print_tracking(cachep, x);
>  	return cachep;
>  }
> +
> +void free_large_kmalloc(struct folio *folio, void *object);
> +
>  #endif /* CONFIG_SLOB */
>  
>  static inline size_t slab_ksize(const struct kmem_cache *s)
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 9c46e2f9589f..0dff46fb7193 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -771,8 +771,8 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
>  
>  /*
>   * kmalloc_info[] is to make slub_debug=,kmalloc-xx option work at boot time.
> - * kmalloc_index() supports up to 2^25=32MB, so the final entry of the table is
> - * kmalloc-32M.
> + * kmalloc_index() supports up to 2^21=2MB, so the final entry of the table is
> + * kmalloc-2M.
>   */
>  const struct kmalloc_info_struct kmalloc_info[] __initconst = {
>  	INIT_KMALLOC_INFO(0, 0),
> @@ -796,11 +796,7 @@ const struct kmalloc_info_struct kmalloc_info[] __initconst = {
>  	INIT_KMALLOC_INFO(262144, 256k),
>  	INIT_KMALLOC_INFO(524288, 512k),
>  	INIT_KMALLOC_INFO(1048576, 1M),
> -	INIT_KMALLOC_INFO(2097152, 2M),
> -	INIT_KMALLOC_INFO(4194304, 4M),
> -	INIT_KMALLOC_INFO(8388608, 8M),
> -	INIT_KMALLOC_INFO(16777216, 16M),
> -	INIT_KMALLOC_INFO(33554432, 32M)
> +	INIT_KMALLOC_INFO(2097152, 2M)
>  };
>  
>  /*
> @@ -913,6 +909,21 @@ void __init create_kmalloc_caches(slab_flags_t flags)
>  	/* Kmalloc array is now usable */
>  	slab_state = UP;
>  }
> +
> +void free_large_kmalloc(struct folio *folio, void *object)
> +{
> +	unsigned int order = folio_order(folio);
> +
> +	if (WARN_ON_ONCE(order == 0))
> +		pr_warn_once("object pointer: 0x%p\n", object);
> +
> +	kmemleak_free(object);
> +	kasan_kfree_large(object);
> +
> +	mod_lruvec_page_state(folio_page(folio, 0), NR_SLAB_UNRECLAIMABLE_B,
> +			      -(PAGE_SIZE << order));
> +	__free_pages(folio_page(folio, 0), order);
> +}
>  #endif /* !CONFIG_SLOB */
>  
>  gfp_t kmalloc_fix_flags(gfp_t flags)
> diff --git a/mm/slub.c b/mm/slub.c
> index 3d02cf44adf7..6cb7ca27f3b7 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1704,12 +1704,6 @@ static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
>   * Hooks for other subsystems that check memory allocations. In a typical
>   * production configuration these hooks all should produce no code at all.
>   */
> -static __always_inline void kfree_hook(void *x)
> -{
> -	kmemleak_free(x);
> -	kasan_kfree_large(x);
> -}
> -
>  static __always_inline bool slab_free_hook(struct kmem_cache *s,
>  						void *x, bool init)
>  {
> @@ -3550,19 +3544,6 @@ struct detached_freelist {
>  	struct kmem_cache *s;
>  };
>  
> -static inline void free_large_kmalloc(struct folio *folio, void *object)
> -{
> -	unsigned int order = folio_order(folio);
> -
> -	if (WARN_ON_ONCE(order == 0))
> -		pr_warn_once("object pointer: 0x%p\n", object);
> -
> -	kfree_hook(object);
> -	mod_lruvec_page_state(folio_page(folio, 0), NR_SLAB_UNRECLAIMABLE_B,
> -			      -(PAGE_SIZE << order));
> -	__free_pages(folio_page(folio, 0), order);
> -}
> -
>  /*
>   * This function progressively scans the array with free objects (with
>   * a limited look ahead) and extract objects belonging to the same