[PATCH v2] mm/zsmalloc: avoid duplicate assignment of prev_class

[PATCH v2] mm/zsmalloc: avoid duplicate assignment of prev_class

[Mahendran Ganesh]

In zs_create_pool(), prev_class is assigned (ZS_SIZE_CLASSES - 1)
times. And the prev_class only references to the previous size_class.
So we do not need unnecessary assignement.

This patch assigns *prev_class* when a new size_class structure
is allocated and uses prev_class to check whether the first class
has been allocated.

Signed-off-by: Mahendran Ganesh <opensource.ganesh@gmail.com>

---
v1 -> v2:
  - follow Dan Streetman's advise to use prev_class to
    check whether the first class has been allocated
  - follow Minchan Kim's advise to remove uninitialized_var()
---
 mm/zsmalloc.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index b3b57ef..810eda1 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -970,7 +970,7 @@ struct zs_pool *zs_create_pool(gfp_t flags)
 		int size;
 		int pages_per_zspage;
 		struct size_class *class;
-		struct size_class *prev_class;
+		struct size_class *prev_class = NULL;
 
 		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
 		if (size > ZS_MAX_ALLOC_SIZE)
@@ -986,8 +986,7 @@ struct zs_pool *zs_create_pool(gfp_t flags)
 		 * characteristics. So, we makes size_class point to
 		 * previous size_class if possible.
 		 */
-		if (i < ZS_SIZE_CLASSES - 1) {
-			prev_class = pool->size_class[i + 1];
+		if (prev_class) {
 			if (can_merge(prev_class, size, pages_per_zspage)) {
 				pool->size_class[i] = prev_class;
 				continue;
@@ -1003,6 +1002,8 @@ struct zs_pool *zs_create_pool(gfp_t flags)
 		class->pages_per_zspage = pages_per_zspage;
 		spin_lock_init(&class->lock);
 		pool->size_class[i] = class;
+
+		prev_class = class;
 	}
 
 	pool->flags = flags;
-- 
1.7.9.5

Re: [PATCH v2] mm/zsmalloc: avoid duplicate assignment of prev_class

[Minchan Kim]

On Fri, Nov 21, 2014 at 09:43:23PM +0800, Mahendran Ganesh wrote:
> In zs_create_pool(), prev_class is assigned (ZS_SIZE_CLASSES - 1)
> times. And the prev_class only references to the previous size_class.
> So we do not need unnecessary assignement.
> 
> This patch assigns *prev_class* when a new size_class structure
> is allocated and uses prev_class to check whether the first class
> has been allocated.
> 
> Signed-off-by: Mahendran Ganesh <opensource.ganesh@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>

-- 
Kind regards,
Minchan Kim

Re: [PATCH v2] mm/zsmalloc: avoid duplicate assignment of prev_class

[Dan Streetman]

On Fri, Nov 21, 2014 at 8:43 AM, Mahendran Ganesh
<opensource.ganesh@gmail.com> wrote:
> In zs_create_pool(), prev_class is assigned (ZS_SIZE_CLASSES - 1)
> times. And the prev_class only references to the previous size_class.
> So we do not need unnecessary assignement.
>
> This patch assigns *prev_class* when a new size_class structure
> is allocated and uses prev_class to check whether the first class
> has been allocated.
>
> Signed-off-by: Mahendran Ganesh <opensource.ganesh@gmail.com>
>
> ---
> v1 -> v2:
>   - follow Dan Streetman's advise to use prev_class to
>     check whether the first class has been allocated
>   - follow Minchan Kim's advise to remove uninitialized_var()
> ---
>  mm/zsmalloc.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index b3b57ef..810eda1 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -970,7 +970,7 @@ struct zs_pool *zs_create_pool(gfp_t flags)
>                 int size;
>                 int pages_per_zspage;
>                 struct size_class *class;
> -               struct size_class *prev_class;
> +               struct size_class *prev_class = NULL;

Maybe I'm looking at the wrong source tree, but I don't think this
will work?  You have to move
prev_class outside the for loop, or it'll be NULL each iteration.

>
>                 size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
>                 if (size > ZS_MAX_ALLOC_SIZE)
> @@ -986,8 +986,7 @@ struct zs_pool *zs_create_pool(gfp_t flags)
>                  * characteristics. So, we makes size_class point to
>                  * previous size_class if possible.
>                  */
> -               if (i < ZS_SIZE_CLASSES - 1) {
> -                       prev_class = pool->size_class[i + 1];
> +               if (prev_class) {
>                         if (can_merge(prev_class, size, pages_per_zspage)) {
>                                 pool->size_class[i] = prev_class;
>                                 continue;
> @@ -1003,6 +1002,8 @@ struct zs_pool *zs_create_pool(gfp_t flags)
>                 class->pages_per_zspage = pages_per_zspage;
>                 spin_lock_init(&class->lock);
>                 pool->size_class[i] = class;
> +
> +               prev_class = class;
>         }
>
>         pool->flags = flags;
> --
> 1.7.9.5
>