Re: [PATCH v1 02/10] zsmalloc: decouple handle and object

[Ganesh Mahendran]

Hello, Minchan

2015-01-21 14:14 GMT+08:00 Minchan Kim <minchan@xxxxxxxxxx>:
> Currently, zram's handle encodes object's location directly so
> it makes hard to support migration/compaction.
>
> This patch decouples handle and object via adding indirect layer.
> For it, it allocates handle dynamically and returns it to user.
> The handle is the address allocated by slab allocation so it's
> unique and the memory allocated keeps object's position so that
> we can get object's position from derefercing handle.
>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
>  mm/zsmalloc.c | 90 ++++++++++++++++++++++++++++++++++++++++++++---------------
>  1 file changed, 68 insertions(+), 22 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 0dec1fa..9436ee8 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -110,6 +110,8 @@
>  #define ZS_MAX_ZSPAGE_ORDER 2
>  #define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER)
>
> +#define ZS_HANDLE_SIZE (sizeof(unsigned long))
> +
>  /*
>   * Object location (<PFN>, <obj_idx>) is encoded as
>   * as single (unsigned long) handle value.
> @@ -241,6 +243,7 @@ struct zs_pool {
>         char *name;
>
>         struct size_class **size_class;
> +       struct kmem_cache *handle_cachep;
>
>         gfp_t flags;    /* allocation flags used when growing pool */
>         atomic_long_t pages_allocated;
> @@ -269,6 +272,34 @@ struct mapping_area {
>         enum zs_mapmode vm_mm; /* mapping mode */
>  };
>
> +static int create_handle_cache(struct zs_pool *pool)
> +{
> +       pool->handle_cachep = kmem_cache_create("zs_handle", ZS_HANDLE_SIZE,
> +                                       0, 0, NULL);
> +       return pool->handle_cachep ? 0 : 1;
> +}
> +
> +static void destroy_handle_cache(struct zs_pool *pool)
> +{
> +       kmem_cache_destroy(pool->handle_cachep);
> +}
> +
> +static unsigned long alloc_handle(struct zs_pool *pool)
> +{
> +       return (unsigned long)kmem_cache_alloc(pool->handle_cachep,
> +               pool->flags & ~__GFP_HIGHMEM);
> +}
> +
> +static void free_handle(struct zs_pool *pool, unsigned long handle)
> +{
> +       kmem_cache_free(pool->handle_cachep, (void *)handle);
> +}
> +
> +static void record_obj(unsigned long handle, unsigned long obj)
> +{
> +       *(unsigned long *)handle = obj;
> +}
> +
>  /* zpool driver */
>
>  #ifdef CONFIG_ZPOOL
> @@ -595,13 +626,18 @@ static void *obj_location_to_handle(struct page *page, unsigned long obj_idx)
>   * decoded obj_idx back to its original value since it was adjusted in
>   * obj_location_to_handle().
>   */
> -static void obj_handle_to_location(unsigned long handle, struct page **page,
> +static void obj_to_location(unsigned long handle, struct page **page,
>                                 unsigned long *obj_idx)
>  {
>         *page = pfn_to_page(handle >> OBJ_INDEX_BITS);
>         *obj_idx = (handle & OBJ_INDEX_MASK) - 1;
>  }
>
> +static unsigned long handle_to_obj(unsigned long handle)
> +{
> +       return *(unsigned long *)handle;
> +}
> +
>  static unsigned long obj_idx_to_offset(struct page *page,
>                                 unsigned long obj_idx, int class_size)
>  {
> @@ -1153,7 +1189,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
>                         enum zs_mapmode mm)
>  {
>         struct page *page;
> -       unsigned long obj_idx, off;
> +       unsigned long obj, obj_idx, off;
>
>         unsigned int class_idx;
>         enum fullness_group fg;
> @@ -1170,7 +1206,8 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
>          */
>         BUG_ON(in_interrupt());
>
> -       obj_handle_to_location(handle, &page, &obj_idx);
> +       obj = handle_to_obj(handle);
> +       obj_to_location(obj, &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);
> @@ -1195,7 +1232,7 @@ 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 obj, obj_idx, off;
>
>         unsigned int class_idx;
>         enum fullness_group fg;
> @@ -1204,7 +1241,8 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>
>         BUG_ON(!handle);
>
> -       obj_handle_to_location(handle, &page, &obj_idx);
> +       obj = handle_to_obj(handle);
> +       obj_to_location(obj, &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);
> @@ -1236,7 +1274,7 @@ EXPORT_SYMBOL_GPL(zs_unmap_object);
>   */
>  unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>  {
> -       unsigned long obj;
> +       unsigned long handle, obj;
>         struct link_free *link;
>         struct size_class *class;
>         void *vaddr;
> @@ -1247,6 +1285,10 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>         if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
>                 return 0;
>
> +       handle = alloc_handle(pool);
> +       if (!handle)
> +               return 0;
> +
>         class = pool->size_class[get_size_class_index(size)];
>
>         spin_lock(&class->lock);
> @@ -1255,8 +1297,10 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>         if (!first_page) {
>                 spin_unlock(&class->lock);
>                 first_page = alloc_zspage(class, pool->flags);
> -               if (unlikely(!first_page))
> +               if (unlikely(!first_page)) {
> +                       free_handle(pool, handle);
>                         return 0;
> +               }
>
>                 set_zspage_mapping(first_page, class->index, ZS_EMPTY);
>                 atomic_long_add(class->pages_per_zspage,
> @@ -1268,7 +1312,7 @@ 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);
> +       obj_to_location(obj, &m_page, &m_objidx);
>         m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);
>
>         vaddr = kmap_atomic(m_page);
> @@ -1281,27 +1325,30 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>         zs_stat_inc(class, OBJ_USED, 1);
>         /* Now move the zspage to another fullness group, if required */
>         fix_fullness_group(pool, first_page);
> +       record_obj(handle, obj);
>         spin_unlock(&class->lock);
>
> -       return obj;
> +       return handle;
>  }
>  EXPORT_SYMBOL_GPL(zs_malloc);
>
> -void zs_free(struct zs_pool *pool, unsigned long obj)
> +void zs_free(struct zs_pool *pool, unsigned long handle)
>  {
>         struct link_free *link;
>         struct page *first_page, *f_page;
> -       unsigned long f_objidx, f_offset;
> +       unsigned long obj, f_objidx, f_offset;
>         void *vaddr;
>
>         int class_idx;
>         struct size_class *class;
>         enum fullness_group fullness;
>
> -       if (unlikely(!obj))
> +       if (unlikely(!handle))
>                 return;
>
> -       obj_handle_to_location(obj, &f_page, &f_objidx);
> +       obj = handle_to_obj(handle);
> +       free_handle(pool, handle);
> +       obj_to_location(obj, &f_page, &f_objidx);
>         first_page = get_first_page(f_page);
>
>         get_zspage_mapping(first_page, &class_idx, &fullness);
> @@ -1356,18 +1403,16 @@ struct zs_pool *zs_create_pool(char *name, gfp_t flags)
>                 return NULL;
>
>         pool->name = kstrdup(name, GFP_KERNEL);
> -       if (!pool->name) {
> -               kfree(pool);
> -               return NULL;
> -       }
> +       if (!pool->name)
> +               goto err;

We can not goto err here. Since in zs_destroy_pool(), the
pool->size_class[x] will
be touched. But it has not been allocated yet.

> +
> +       if (create_handle_cache(pool))
> +               goto err;
>
>         pool->size_class = kcalloc(zs_size_classes, sizeof(struct size_class *),
>                         GFP_KERNEL);
> -       if (!pool->size_class) {
> -               kfree(pool->name);
> -               kfree(pool);
> -               return NULL;
> -       }
> +       if (!pool->size_class)
> +               goto err;
>
>         /*
>          * Iterate reversly, because, size of size_class that we want to use
> @@ -1450,6 +1495,7 @@ void zs_destroy_pool(struct zs_pool *pool)
>                 kfree(class);
>         }
>
> +       destroy_handle_cache(pool);
>         kfree(pool->size_class);
>         kfree(pool->name);
>         kfree(pool);
> --
> 1.9.3
>
> --
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