2014-11-25 13:01:03

by Ganesh Mahendran

Subject: [PATCH v3] mm/zsmalloc: avoid duplicate assignment of prev_class

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: Ganesh Mahendran <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Nitin Gupta <[email protected]>
Cc: Dan Streetman <[email protected]>

---
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()

v2 -> v3:
- move *prev_class* definition out of the loop - Dan
---
mm/zsmalloc.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 83ecdb6..de1320e 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -966,6 +966,7 @@ struct zs_pool *zs_create_pool(gfp_t flags)
{
int i, ovhd_size;
struct zs_pool *pool;
+ struct size_class *prev_class = NULL;

ovhd_size = roundup(sizeof(*pool), PAGE_SIZE);
pool = kzalloc(ovhd_size, GFP_KERNEL);
@@ -980,7 +981,6 @@ struct zs_pool *zs_create_pool(gfp_t flags)
int size;
int pages_per_zspage;
struct size_class *class;
- struct size_class *prev_class;

size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
if (size > ZS_MAX_ALLOC_SIZE)
@@ -996,8 +996,7 @@ 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;
@@ -1013,6 +1012,8 @@ 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

2014-11-25 15:40:38

by Dan Streetman

Subject: Re: [PATCH v3] mm/zsmalloc: avoid duplicate assignment of prev_class

On Tue, Nov 25, 2014 at 8:00 AM, Ganesh Mahendran
<[email protected]> 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: Ganesh Mahendran <[email protected]>
> Cc: Minchan Kim <[email protected]>
> Cc: Nitin Gupta <[email protected]>
> Cc: Dan Streetman <[email protected]>

Reviewed-by: Dan Streetman <[email protected]>

>
> ---
> 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()
>
> v2 -> v3:
> - move *prev_class* definition out of the loop - Dan
> ---
> mm/zsmalloc.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 83ecdb6..de1320e 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -966,6 +966,7 @@ struct zs_pool *zs_create_pool(gfp_t flags)
> {
> int i, ovhd_size;
> struct zs_pool *pool;
> + struct size_class *prev_class = NULL;
>
> ovhd_size = roundup(sizeof(*pool), PAGE_SIZE);
> pool = kzalloc(ovhd_size, GFP_KERNEL);
> @@ -980,7 +981,6 @@ struct zs_pool *zs_create_pool(gfp_t flags)
> int size;
> int pages_per_zspage;
> struct size_class *class;
> - struct size_class *prev_class;
>
> size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
> if (size > ZS_MAX_ALLOC_SIZE)
> @@ -996,8 +996,7 @@ 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;
> @@ -1013,6 +1012,8 @@ 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
>