Re: [PATCH v2 1/2] zsmalloc: add function to query object size

[Minchan Kim <minchan@kernel.org>]

Sorry for late response. I should have hurried.
I just sent by my comment of your previous version's mail thread.
Please look at it.

On Wed, Nov 28, 2012 at 11:48:30PM -0800, Nitin Gupta wrote:
> Changelog v2 vs v1
>  - None
> 
> Adds zs_get_object_size(handle) which provides the size of
> the given object. This is useful since the user (zram etc.)
> now do not have to maintain object sizes separately, saving
> on some metadata size (4b per page).
> 
> The object handle encodes <page, offset> pair which currently points
> to the start of the object. Now, the handle implicitly stores the size
> information by pointing to the object's end instead. Since zsmalloc is
> a slab based allocator, the start of the object can be easily determined
> and the difference between the end offset encoded in the handle and the
> start gives us the object size.
> 
> Signed-off-by: Nitin Gupta <ngupta@vflare.org>
> ---
>  drivers/staging/zsmalloc/zsmalloc-main.c |  177 +++++++++++++++++++++---------
>  drivers/staging/zsmalloc/zsmalloc.h      |    1 +
>  2 files changed, 127 insertions(+), 51 deletions(-)
> 
> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
> index 09a9d35..65c9d3b 100644
> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
> @@ -112,20 +112,20 @@
>  #define MAX_PHYSMEM_BITS 36
>  #else /* !CONFIG_HIGHMEM64G */
>  /*
> - * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
> + * If this definition of MAX_PHYSMEM_BITS is used, OFFSET_BITS will just
>   * be PAGE_SHIFT
>   */
>  #define MAX_PHYSMEM_BITS BITS_PER_LONG
>  #endif
>  #endif
>  #define _PFN_BITS		(MAX_PHYSMEM_BITS - PAGE_SHIFT)
> -#define OBJ_INDEX_BITS	(BITS_PER_LONG - _PFN_BITS)
> -#define OBJ_INDEX_MASK	((_AC(1, UL) << OBJ_INDEX_BITS) - 1)
> +#define OFFSET_BITS	(BITS_PER_LONG - _PFN_BITS)
> +#define OFFSET_MASK	((_AC(1, UL) << OFFSET_BITS) - 1)
>  
>  #define MAX(a, b) ((a) >= (b) ? (a) : (b))
>  /* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
>  #define ZS_MIN_ALLOC_SIZE \
> -	MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
> +	MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OFFSET_BITS))
>  #define ZS_MAX_ALLOC_SIZE	PAGE_SIZE
>  
>  /*
> @@ -256,6 +256,11 @@ static int is_last_page(struct page *page)
>  	return PagePrivate2(page);
>  }
>  
> +static unsigned long get_page_index(struct page *page)
> +{
> +	return is_first_page(page) ? 0 : page->index;
> +}
> +
>  static void get_zspage_mapping(struct page *page, unsigned int *class_idx,
>  				enum fullness_group *fullness)
>  {
> @@ -433,39 +438,86 @@ static struct page *get_next_page(struct page *page)
>  	return next;
>  }
>  
> -/* Encode <page, obj_idx> as a single handle value */
> -static void *obj_location_to_handle(struct page *page, unsigned long obj_idx)
> +static struct page *get_prev_page(struct page *page)
>  {
> -	unsigned long handle;
> +	struct page *prev, *first_page;
>  
> -	if (!page) {
> -		BUG_ON(obj_idx);
> -		return NULL;
> -	}
> +	first_page = get_first_page(page);
> +	if (page == first_page)
> +		prev = NULL;
> +	else if (page == (struct page *)first_page->private)
> +		prev = first_page;
> +	else
> +		prev = list_entry(page->lru.prev, struct page, lru);
>  
> -	handle = page_to_pfn(page) << OBJ_INDEX_BITS;
> -	handle |= (obj_idx & OBJ_INDEX_MASK);
> +	return prev;
>  
> -	return (void *)handle;
>  }
>  
> -/* Decode <page, obj_idx> pair from the given object handle */
> -static void obj_handle_to_location(unsigned long handle, struct page **page,
> -				unsigned long *obj_idx)
> +static void *encode_ptr(struct page *page, unsigned long offset)
>  {
> -	*page = pfn_to_page(handle >> OBJ_INDEX_BITS);
> -	*obj_idx = handle & OBJ_INDEX_MASK;
> +	unsigned long ptr;
> +	ptr = page_to_pfn(page) << OFFSET_BITS;
> +	ptr |= offset & OFFSET_MASK;
> +	return (void *)ptr;
> +}
> +
> +static void decode_ptr(unsigned long ptr, struct page **page,
> +					unsigned int *offset)
> +{
> +	*page = pfn_to_page(ptr >> OFFSET_BITS);
> +	*offset = ptr & OFFSET_MASK;
> +}
> +
> +static struct page *obj_handle_to_page(unsigned long handle)
> +{
> +	struct page *page;
> +	unsigned int offset;
> +
> +	decode_ptr(handle, &page, &offset);
> +	if (offset < get_page_index(page))
> +		page = get_prev_page(page);
> +
> +	return page;
> +}
> +
> +static unsigned int obj_handle_to_offset(unsigned long handle,
> +					unsigned int class_size)
> +{
> +	struct page *page;
> +	unsigned int offset;
> +
> +	decode_ptr(handle, &page, &offset);
> +	if (offset < get_page_index(page))
> +		offset = PAGE_SIZE - class_size + get_page_index(page);
> +	else
> +		offset = roundup(offset, class_size) - class_size;
> +
> +	return offset;
>  }
>  
> -static unsigned long obj_idx_to_offset(struct page *page,
> -				unsigned long obj_idx, int class_size)
> +/* Encode <page, offset, size> as a single handle value */
> +static void *obj_location_to_handle(struct page *page, unsigned int offset,
> +				unsigned int size, unsigned int class_size)
>  {
> -	unsigned long off = 0;
> +	struct page *endpage;
> +	unsigned int endoffset;
>  
> -	if (!is_first_page(page))
> -		off = page->index;
> +	if (!page) {
> +		BUG_ON(offset);
> +		return NULL;
> +	}
> +	BUG_ON(offset >= PAGE_SIZE);
> +
> +	endpage = page;
> +	endoffset = offset + size - 1;
> +	if (endoffset >= PAGE_SIZE) {
> +		endpage = get_next_page(page);
> +		BUG_ON(!endpage);
> +		endoffset -= PAGE_SIZE;
> +	}
>  
> -	return off + obj_idx * class_size;
> +	return encode_ptr(endpage, endoffset);
>  }
>  
>  static void reset_page(struct page *page)
> @@ -506,14 +558,13 @@ static void free_zspage(struct page *first_page)
>  /* Initialize a newly allocated zspage */
>  static void init_zspage(struct page *first_page, struct size_class *class)
>  {
> -	unsigned long off = 0;
> +	unsigned long off = 0, next_off = 0;
>  	struct page *page = first_page;
>  
>  	BUG_ON(!is_first_page(first_page));
>  	while (page) {
>  		struct page *next_page;
>  		struct link_free *link;
> -		unsigned int i, objs_on_page;
>  
>  		/*
>  		 * page->index stores offset of first object starting
> @@ -526,14 +577,12 @@ static void init_zspage(struct page *first_page, struct size_class *class)
>  
>  		link = (struct link_free *)kmap_atomic(page) +
>  						off / sizeof(*link);
> -		objs_on_page = (PAGE_SIZE - off) / class->size;
>  
> -		for (i = 1; i <= objs_on_page; i++) {
> -			off += class->size;
> -			if (off < PAGE_SIZE) {
> -				link->next = obj_location_to_handle(page, i);
> -				link += class->size / sizeof(*link);
> -			}
> +		next_off = off + class->size;
> +		while (next_off < PAGE_SIZE) {
> +			link->next = encode_ptr(page, next_off);
> +			link += class->size / sizeof(*link);
> +			next_off += class->size;
>  		}
>  
>  		/*
> @@ -542,10 +591,11 @@ static void init_zspage(struct page *first_page, struct size_class *class)
>  		 * page (if present)
>  		 */
>  		next_page = get_next_page(page);
> -		link->next = obj_location_to_handle(next_page, 0);
> +		next_off = next_page ? next_off - PAGE_SIZE : 0;
> +		link->next = encode_ptr(next_page, next_off);
>  		kunmap_atomic(link);
>  		page = next_page;
> -		off = (off + class->size) % PAGE_SIZE;
> +		off = next_off;
>  	}
>  }
>  
> @@ -596,7 +646,7 @@ static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
>  
>  	init_zspage(first_page, class);
>  
> -	first_page->freelist = obj_location_to_handle(first_page, 0);
> +	first_page->freelist = encode_ptr(first_page, 0);
>  	/* Maximum number of objects we can store in this zspage */
>  	first_page->objects = class->pages_per_zspage * PAGE_SIZE / class->size;
>  
> @@ -871,7 +921,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>  	struct size_class *class;
>  
>  	struct page *first_page, *m_page;
> -	unsigned long m_objidx, m_offset;
> +	unsigned int m_offset;
>  
>  	if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
>  		return 0;
> @@ -895,8 +945,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>  	}
>  
>  	obj = (unsigned long)first_page->freelist;
> -	obj_handle_to_location(obj, &m_page, &m_objidx);
> -	m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);
> +	decode_ptr(obj, &m_page, &m_offset);
>  
>  	link = (struct link_free *)kmap_atomic(m_page) +
>  					m_offset / sizeof(*link);
> @@ -907,6 +956,9 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>  	first_page->inuse++;
>  	/* Now move the zspage to another fullness group, if required */
>  	fix_fullness_group(pool, first_page);
> +
> +	obj = (unsigned long)obj_location_to_handle(m_page, m_offset,
> +						size, class->size);
>  	spin_unlock(&class->lock);
>  
>  	return obj;
> @@ -917,7 +969,7 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
>  {
>  	struct link_free *link;
>  	struct page *first_page, *f_page;
> -	unsigned long f_objidx, f_offset;
> +	unsigned long f_offset;
>  
>  	int class_idx;
>  	struct size_class *class;
> @@ -926,12 +978,12 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
>  	if (unlikely(!obj))
>  		return;
>  
> -	obj_handle_to_location(obj, &f_page, &f_objidx);
> +	f_page = obj_handle_to_page(obj);
>  	first_page = get_first_page(f_page);
>  
>  	get_zspage_mapping(first_page, &class_idx, &fullness);
>  	class = &pool->size_class[class_idx];
> -	f_offset = obj_idx_to_offset(f_page, f_objidx, class->size);
> +	f_offset = obj_handle_to_offset(obj, class->size);
>  
>  	spin_lock(&class->lock);
>  
> @@ -940,7 +992,7 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
>  							+ f_offset);
>  	link->next = first_page->freelist;
>  	kunmap_atomic(link);
> -	first_page->freelist = (void *)obj;
> +	first_page->freelist = encode_ptr(f_page, f_offset);
>  
>  	first_page->inuse--;
>  	fullness = fix_fullness_group(pool, first_page);
> @@ -970,10 +1022,10 @@ EXPORT_SYMBOL_GPL(zs_free);
>   * This function returns with preemption and page faults disabled.
>  */
>  void *zs_map_object(struct zs_pool *pool, unsigned long handle,
> -			enum zs_mapmode mm)
> +					enum zs_mapmode mm)
>  {
>  	struct page *page;
> -	unsigned long obj_idx, off;
> +	unsigned long off;
>  
>  	unsigned int class_idx;
>  	enum fullness_group fg;
> @@ -990,10 +1042,10 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
>  	 */
>  	BUG_ON(in_interrupt());
>  
> -	obj_handle_to_location(handle, &page, &obj_idx);
> +	page = obj_handle_to_page(handle);
>  	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);
> +	off = obj_handle_to_offset(handle, class->size);
>  
>  	area = &get_cpu_var(zs_map_area);
>  	area->vm_mm = mm;
> @@ -1015,7 +1067,7 @@ EXPORT_SYMBOL_GPL(zs_map_object);
>  void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>  {
>  	struct page *page;
> -	unsigned long obj_idx, off;
> +	unsigned long off;
>  
>  	unsigned int class_idx;
>  	enum fullness_group fg;
> @@ -1024,10 +1076,10 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>  
>  	BUG_ON(!handle);
>  
> -	obj_handle_to_location(handle, &page, &obj_idx);
> +	page = obj_handle_to_page(handle);
>  	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);
> +	off = obj_handle_to_offset(handle, class->size);
>  
>  	area = &__get_cpu_var(zs_map_area);
>  	if (off + class->size <= PAGE_SIZE)
> @@ -1045,6 +1097,29 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>  }
>  EXPORT_SYMBOL_GPL(zs_unmap_object);
>  
> +size_t zs_get_object_size(struct zs_pool *pool, unsigned long handle)
> +{
> +	struct page *endpage;
> +	unsigned int endoffset, size;
> +
> +	unsigned int class_idx;
> +	enum fullness_group fg;
> +	struct size_class *class;
> +
> +	decode_ptr(handle, &endpage, &endoffset);
> +	get_zspage_mapping(endpage, &class_idx, &fg);
> +	class = &pool->size_class[class_idx];
> +
> +	size = endoffset + 1;
> +	if (endoffset < get_page_index(endpage))
> +		size += class->size - get_page_index(endpage);
> +	else
> +		size -= rounddown(endoffset, class->size);
> +
> +	return size;
> +}
> +EXPORT_SYMBOL_GPL(zs_get_object_size);
> +
>  u64 zs_get_total_size_bytes(struct zs_pool *pool)
>  {
>  	int i;
> diff --git a/drivers/staging/zsmalloc/zsmalloc.h b/drivers/staging/zsmalloc/zsmalloc.h
> index de2e8bf..2830fdf 100644
> --- a/drivers/staging/zsmalloc/zsmalloc.h
> +++ b/drivers/staging/zsmalloc/zsmalloc.h
> @@ -38,6 +38,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
>  			enum zs_mapmode mm);
>  void zs_unmap_object(struct zs_pool *pool, unsigned long handle);
>  
> +size_t zs_get_object_size(struct zs_pool *pool, unsigned long handle);
>  u64 zs_get_total_size_bytes(struct zs_pool *pool);
>  
>  #endif
> -- 
> 1.7.10.4
> 
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-- 
Kind regards,
Minchan Kim