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Date:	Tue, 16 Dec 2014 09:40:33 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:	ngupta@...are.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/zsmalloc: adjust order of functions

Hello Ganesh,

On Sat, Dec 13, 2014 at 09:43:23PM +0800, Ganesh Mahendran wrote:
> Currently functions in zsmalloc.c does not arranged in a readable
> and reasonable sequence. With the more and more functions added,
> we may meet below inconvenience. For example:
> 
> Current functions:
>     void zs_init()
>     {
>     }
> 
>     static void get_maxobj_per_zspage()
>     {
>     }
> 
> Then I want to add a func_1() which is called from zs_init(), and this new added
> function func_1() will used get_maxobj_per_zspage() which is defined below zs_init().
> 
>     void func_1()
>     {
>         get_maxobj_per_zspage()
>     }
> 
>     void zs_init()
>     {
>         func_1()
>     }
> 
>     static void get_maxobj_per_zspage()
>     {
>     }
> 
> This will cause compiling issue. So we must add a declaration:
>     static void get_maxobj_per_zspage();
> before func_1() if we do not put get_maxobj_per_zspage() before func_1().

Yes, I suffered from that when I made compaction but was not sure
it's it was obviously wrong.
Stupid question:
What's the problem if we should put function declaration on top of
source code?

> 
> In addition, puting module_[init|exit] functions at the bottom of the file
> conforms to our habit.

Normally, we do but without any strong reason, I don't want to rub git-blame
by clean up patches.

In summary, I like this patch but don't like to churn git-blame by clean-up
patchset without strong reason so I need something I am sure.

> 
> So, this patch ajusts function sequence as:
>     /* helper functions */
>     ...
>     obj_location_to_handle()
>     ...
> 
>     /* Some exported functions */
>     ...
> 
>     zs_map_object()
>     zs_unmap_object()
> 
>     zs_malloc()
>     zs_free()
> 
>     zs_init()
>     zs_exit()
> 
> Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.com>
> ---
>  mm/zsmalloc.c |  374 ++++++++++++++++++++++++++++-----------------------------
>  1 file changed, 187 insertions(+), 187 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 4d0a063..b724039 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -884,19 +884,6 @@ static struct notifier_block zs_cpu_nb = {
>  	.notifier_call = zs_cpu_notifier
>  };
>  
> -static void zs_unregister_cpu_notifier(void)
> -{
> -	int cpu;
> -
> -	cpu_notifier_register_begin();
> -
> -	for_each_online_cpu(cpu)
> -		zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
> -	__unregister_cpu_notifier(&zs_cpu_nb);
> -
> -	cpu_notifier_register_done();
> -}
> -
>  static int zs_register_cpu_notifier(void)
>  {
>  	int cpu, uninitialized_var(ret);
> @@ -914,40 +901,28 @@ static int zs_register_cpu_notifier(void)
>  	return notifier_to_errno(ret);
>  }
>  
> -static void init_zs_size_classes(void)
> +static void zs_unregister_cpu_notifier(void)
>  {
> -	int nr;
> +	int cpu;
>  
> -	nr = (ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / ZS_SIZE_CLASS_DELTA + 1;
> -	if ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) % ZS_SIZE_CLASS_DELTA)
> -		nr += 1;
> +	cpu_notifier_register_begin();
>  
> -	zs_size_classes = nr;
> -}
> +	for_each_online_cpu(cpu)
> +		zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
> +	__unregister_cpu_notifier(&zs_cpu_nb);
>  
> -static void __exit zs_exit(void)
> -{
> -#ifdef CONFIG_ZPOOL
> -	zpool_unregister_driver(&zs_zpool_driver);
> -#endif
> -	zs_unregister_cpu_notifier();
> +	cpu_notifier_register_done();
>  }
>  
> -static int __init zs_init(void)
> +static void init_zs_size_classes(void)
>  {
> -	int ret = zs_register_cpu_notifier();
> -
> -	if (ret) {
> -		zs_unregister_cpu_notifier();
> -		return ret;
> -	}
> +	int nr;
>  
> -	init_zs_size_classes();
> +	nr = (ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / ZS_SIZE_CLASS_DELTA + 1;
> +	if ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) % ZS_SIZE_CLASS_DELTA)
> +		nr += 1;
>  
> -#ifdef CONFIG_ZPOOL
> -	zpool_register_driver(&zs_zpool_driver);
> -#endif
> -	return 0;
> +	zs_size_classes = nr;
>  }
>  
>  static unsigned int get_maxobj_per_zspage(int size, int pages_per_zspage)
> @@ -967,113 +942,101 @@ static bool can_merge(struct size_class *prev, int size, int pages_per_zspage)
>  	return true;
>  }
>  
> +unsigned long zs_get_total_pages(struct zs_pool *pool)
> +{
> +	return atomic_long_read(&pool->pages_allocated);
> +}
> +EXPORT_SYMBOL_GPL(zs_get_total_pages);
> +
>  /**
> - * zs_create_pool - Creates an allocation pool to work from.
> - * @flags: allocation flags used to allocate pool metadata
> + * zs_map_object - get address of allocated object from handle.
> + * @pool: pool from which the object was allocated
> + * @handle: handle returned from zs_malloc
>   *
> - * This function must be called before anything when using
> - * the zsmalloc allocator.
> + * Before using an object allocated from zs_malloc, it must be mapped using
> + * this function. When done with the object, it must be unmapped using
> + * zs_unmap_object.
>   *
> - * On success, a pointer to the newly created pool is returned,
> - * otherwise NULL.
> + * Only one object can be mapped per cpu at a time. There is no protection
> + * against nested mappings.
> + *
> + * This function returns with preemption and page faults disabled.
>   */
> -struct zs_pool *zs_create_pool(gfp_t flags)
> +void *zs_map_object(struct zs_pool *pool, unsigned long handle,
> +			enum zs_mapmode mm)
>  {
> -	int i;
> -	struct zs_pool *pool;
> -	struct size_class *prev_class = NULL;
> +	struct page *page;
> +	unsigned long obj_idx, off;
>  
> -	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
> -	if (!pool)
> -		return NULL;
> +	unsigned int class_idx;
> +	enum fullness_group fg;
> +	struct size_class *class;
> +	struct mapping_area *area;
> +	struct page *pages[2];
>  
> -	pool->size_class = kcalloc(zs_size_classes, sizeof(struct size_class *),
> -			GFP_KERNEL);
> -	if (!pool->size_class) {
> -		kfree(pool);
> -		return NULL;
> -	}
> +	BUG_ON(!handle);
>  
>  	/*
> -	 * Iterate reversly, because, size of size_class that we want to use
> -	 * for merging should be larger or equal to current size.
> +	 * Because we use per-cpu mapping areas shared among the
> +	 * pools/users, we can't allow mapping in interrupt context
> +	 * because it can corrupt another users mappings.
>  	 */
> -	for (i = zs_size_classes - 1; i >= 0; i--) {
> -		int size;
> -		int pages_per_zspage;
> -		struct size_class *class;
> -
> -		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
> -		if (size > ZS_MAX_ALLOC_SIZE)
> -			size = ZS_MAX_ALLOC_SIZE;
> -		pages_per_zspage = get_pages_per_zspage(size);
> -
> -		/*
> -		 * size_class is used for normal zsmalloc operation such
> -		 * as alloc/free for that size. Although it is natural that we
> -		 * have one size_class for each size, there is a chance that we
> -		 * can get more memory utilization if we use one size_class for
> -		 * many different sizes whose size_class have same
> -		 * characteristics. So, we makes size_class point to
> -		 * previous size_class if possible.
> -		 */
> -		if (prev_class) {
> -			if (can_merge(prev_class, size, pages_per_zspage)) {
> -				pool->size_class[i] = prev_class;
> -				continue;
> -			}
> -		}
> -
> -		class = kzalloc(sizeof(struct size_class), GFP_KERNEL);
> -		if (!class)
> -			goto err;
> +	BUG_ON(in_interrupt());
>  
> -		class->size = size;
> -		class->index = i;
> -		class->pages_per_zspage = pages_per_zspage;
> -		spin_lock_init(&class->lock);
> -		pool->size_class[i] = class;
> +	obj_handle_to_location(handle, &page, &obj_idx);
> +	get_zspage_mapping(get_first_page(page), &class_idx, &fg);
> +	class = pool->size_class[class_idx];
> +	off = obj_idx_to_offset(page, obj_idx, class->size);
>  
> -		prev_class = class;
> +	area = &get_cpu_var(zs_map_area);
> +	area->vm_mm = mm;
> +	if (off + class->size <= PAGE_SIZE) {
> +		/* this object is contained entirely within a page */
> +		area->vm_addr = kmap_atomic(page);
> +		return area->vm_addr + off;
>  	}
>  
> -	pool->flags = flags;
> -
> -	return pool;
> +	/* this object spans two pages */
> +	pages[0] = page;
> +	pages[1] = get_next_page(page);
> +	BUG_ON(!pages[1]);
>  
> -err:
> -	zs_destroy_pool(pool);
> -	return NULL;
> +	return __zs_map_object(area, pages, off, class->size);
>  }
> -EXPORT_SYMBOL_GPL(zs_create_pool);
> +EXPORT_SYMBOL_GPL(zs_map_object);
>  
> -void zs_destroy_pool(struct zs_pool *pool)
> +void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>  {
> -	int i;
> +	struct page *page;
> +	unsigned long obj_idx, off;
>  
> -	for (i = 0; i < zs_size_classes; i++) {
> -		int fg;
> -		struct size_class *class = pool->size_class[i];
> +	unsigned int class_idx;
> +	enum fullness_group fg;
> +	struct size_class *class;
> +	struct mapping_area *area;
>  
> -		if (!class)
> -			continue;
> +	BUG_ON(!handle);
>  
> -		if (class->index != i)
> -			continue;
> +	obj_handle_to_location(handle, &page, &obj_idx);
> +	get_zspage_mapping(get_first_page(page), &class_idx, &fg);
> +	class = pool->size_class[class_idx];
> +	off = obj_idx_to_offset(page, obj_idx, class->size);
>  
> -		for (fg = 0; fg < _ZS_NR_FULLNESS_GROUPS; fg++) {
> -			if (class->fullness_list[fg]) {
> -				pr_info("Freeing non-empty class with size %db, fullness group %d\n",
> -					class->size, fg);
> -			}
> -		}
> -		kfree(class);
> -	}
> +	area = this_cpu_ptr(&zs_map_area);
> +	if (off + class->size <= PAGE_SIZE)
> +		kunmap_atomic(area->vm_addr);
> +	else {
> +		struct page *pages[2];
>  
> -	kfree(pool->size_class);
> -	kfree(pool);
> +		pages[0] = page;
> +		pages[1] = get_next_page(page);
> +		BUG_ON(!pages[1]);
> +
> +		__zs_unmap_object(area, pages, off, class->size);
> +	}
> +	put_cpu_var(zs_map_area);
>  }
> -EXPORT_SYMBOL_GPL(zs_destroy_pool);
> +EXPORT_SYMBOL_GPL(zs_unmap_object);
>  
>  /**
>   * zs_malloc - Allocate block of given size from pool.
> @@ -1176,100 +1139,137 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
>  EXPORT_SYMBOL_GPL(zs_free);
>  
>  /**
> - * zs_map_object - get address of allocated object from handle.
> - * @pool: pool from which the object was allocated
> - * @handle: handle returned from zs_malloc
> - *
> - * Before using an object allocated from zs_malloc, it must be mapped using
> - * this function. When done with the object, it must be unmapped using
> - * zs_unmap_object.
> + * zs_create_pool - Creates an allocation pool to work from.
> + * @flags: allocation flags used to allocate pool metadata
>   *
> - * Only one object can be mapped per cpu at a time. There is no protection
> - * against nested mappings.
> + * This function must be called before anything when using
> + * the zsmalloc allocator.
>   *
> - * This function returns with preemption and page faults disabled.
> + * On success, a pointer to the newly created pool is returned,
> + * otherwise NULL.
>   */
> -void *zs_map_object(struct zs_pool *pool, unsigned long handle,
> -			enum zs_mapmode mm)
> +struct zs_pool *zs_create_pool(gfp_t flags)
>  {
> -	struct page *page;
> -	unsigned long obj_idx, off;
> +	int i;
> +	struct zs_pool *pool;
> +	struct size_class *prev_class = NULL;
>  
> -	unsigned int class_idx;
> -	enum fullness_group fg;
> -	struct size_class *class;
> -	struct mapping_area *area;
> -	struct page *pages[2];
> +	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
> +	if (!pool)
> +		return NULL;
>  
> -	BUG_ON(!handle);
> +	pool->size_class = kcalloc(zs_size_classes, sizeof(struct size_class *),
> +			GFP_KERNEL);
> +	if (!pool->size_class) {
> +		kfree(pool);
> +		return NULL;
> +	}
>  
>  	/*
> -	 * Because we use per-cpu mapping areas shared among the
> -	 * pools/users, we can't allow mapping in interrupt context
> -	 * because it can corrupt another users mappings.
> +	 * Iterate reversly, because, size of size_class that we want to use
> +	 * for merging should be larger or equal to current size.
>  	 */
> -	BUG_ON(in_interrupt());
> +	for (i = zs_size_classes - 1; i >= 0; i--) {
> +		int size;
> +		int pages_per_zspage;
> +		struct size_class *class;
>  
> -	obj_handle_to_location(handle, &page, &obj_idx);
> -	get_zspage_mapping(get_first_page(page), &class_idx, &fg);
> -	class = pool->size_class[class_idx];
> -	off = obj_idx_to_offset(page, obj_idx, class->size);
> +		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
> +		if (size > ZS_MAX_ALLOC_SIZE)
> +			size = ZS_MAX_ALLOC_SIZE;
> +		pages_per_zspage = get_pages_per_zspage(size);
>  
> -	area = &get_cpu_var(zs_map_area);
> -	area->vm_mm = mm;
> -	if (off + class->size <= PAGE_SIZE) {
> -		/* this object is contained entirely within a page */
> -		area->vm_addr = kmap_atomic(page);
> -		return area->vm_addr + off;
> +		/*
> +		 * size_class is used for normal zsmalloc operation such
> +		 * as alloc/free for that size. Although it is natural that we
> +		 * have one size_class for each size, there is a chance that we
> +		 * can get more memory utilization if we use one size_class for
> +		 * many different sizes whose size_class have same
> +		 * characteristics. So, we makes size_class point to
> +		 * previous size_class if possible.
> +		 */
> +		if (prev_class) {
> +			if (can_merge(prev_class, size, pages_per_zspage)) {
> +				pool->size_class[i] = prev_class;
> +				continue;
> +			}
> +		}
> +
> +		class = kzalloc(sizeof(struct size_class), GFP_KERNEL);
> +		if (!class)
> +			goto err;
> +
> +		class->size = size;
> +		class->index = i;
> +		class->pages_per_zspage = pages_per_zspage;
> +		spin_lock_init(&class->lock);
> +		pool->size_class[i] = class;
> +
> +		prev_class = class;
>  	}
>  
> -	/* this object spans two pages */
> -	pages[0] = page;
> -	pages[1] = get_next_page(page);
> -	BUG_ON(!pages[1]);
> +	pool->flags = flags;
>  
> -	return __zs_map_object(area, pages, off, class->size);
> +	return pool;
> +
> +err:
> +	zs_destroy_pool(pool);
> +	return NULL;
>  }
> -EXPORT_SYMBOL_GPL(zs_map_object);
> +EXPORT_SYMBOL_GPL(zs_create_pool);
>  
> -void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
> +void zs_destroy_pool(struct zs_pool *pool)
>  {
> -	struct page *page;
> -	unsigned long obj_idx, off;
> +	int i;
>  
> -	unsigned int class_idx;
> -	enum fullness_group fg;
> -	struct size_class *class;
> -	struct mapping_area *area;
> +	for (i = 0; i < zs_size_classes; i++) {
> +		int fg;
> +		struct size_class *class = pool->size_class[i];
>  
> -	BUG_ON(!handle);
> +		if (!class)
> +			continue;
>  
> -	obj_handle_to_location(handle, &page, &obj_idx);
> -	get_zspage_mapping(get_first_page(page), &class_idx, &fg);
> -	class = pool->size_class[class_idx];
> -	off = obj_idx_to_offset(page, obj_idx, class->size);
> +		if (class->index != i)
> +			continue;
>  
> -	area = this_cpu_ptr(&zs_map_area);
> -	if (off + class->size <= PAGE_SIZE)
> -		kunmap_atomic(area->vm_addr);
> -	else {
> -		struct page *pages[2];
> +		for (fg = 0; fg < _ZS_NR_FULLNESS_GROUPS; fg++) {
> +			if (class->fullness_list[fg]) {
> +				pr_info("Freeing non-empty class with size %db, fullness group %d\n",
> +					class->size, fg);
> +			}
> +		}
> +		kfree(class);
> +	}
>  
> -		pages[0] = page;
> -		pages[1] = get_next_page(page);
> -		BUG_ON(!pages[1]);
> +	kfree(pool->size_class);
> +	kfree(pool);
> +}
> +EXPORT_SYMBOL_GPL(zs_destroy_pool);
>  
> -		__zs_unmap_object(area, pages, off, class->size);
> +static int __init zs_init(void)
> +{
> +	int ret = zs_register_cpu_notifier();
> +
> +	if (ret) {
> +		zs_unregister_cpu_notifier();
> +		return ret;
>  	}
> -	put_cpu_var(zs_map_area);
> +
> +	init_zs_size_classes();
> +
> +#ifdef CONFIG_ZPOOL
> +	zpool_register_driver(&zs_zpool_driver);
> +#endif
> +	return 0;
>  }
> -EXPORT_SYMBOL_GPL(zs_unmap_object);
>  
> -unsigned long zs_get_total_pages(struct zs_pool *pool)
> +static void __exit zs_exit(void)
>  {
> -	return atomic_long_read(&pool->pages_allocated);
> +#ifdef CONFIG_ZPOOL
> +	zpool_unregister_driver(&zs_zpool_driver);
> +#endif
> +	zs_unregister_cpu_notifier();
>  }
> -EXPORT_SYMBOL_GPL(zs_get_total_pages);
>  
>  module_init(zs_init);
>  module_exit(zs_exit);
> -- 
> 1.7.9.5
> 
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