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Message-ID: <CADAEsF8BpCxYOCwp6mG75N9R8L-xVd1kvvD7+oV12gLs7RGXQw@mail.gmail.com>
Date: Mon, 26 Jan 2015 10:53:57 +0800
From: Ganesh Mahendran <opensource.ganesh@...il.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>, Dan Streetman <ddstreet@...e.org>,
Seth Jennings <sjennings@...iantweb.net>,
Nitin Gupta <ngupta@...are.org>,
Juneho Choi <juno.choi@....com>, Gunho Lee <gunho.lee@....com>,
Luigi Semenzato <semenzato@...gle.com>,
Jerome Marchand <jmarchan@...hat.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH v1 02/10] zsmalloc: decouple handle and object
Hello, Minchan
2015-01-21 14:14 GMT+08:00 Minchan Kim <minchan@...nel.org>:
> 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@...nel.org>
> ---
> 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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