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

2014-11-21 11:22 GMT+08:00 Dan Streetman <ddstreet@ieee.org>:
> On Thu, Nov 20, 2014 at 8:08 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 alloc
>> size_class. So we do not need unnecessary assignement.
>>
>> This patch modifies *prev_class* to *prev_alloc_class*. And the
>> *prev_alloc_class* will only be assigned when a new size_class
>> structure is allocated.
>>
>> Signed-off-by: Mahendran Ganesh <opensource.ganesh@gmail.com>
>> ---
>> mm/zsmalloc.c | 9 +++++----
>> 1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
>> index b3b57ef..ac2b396 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 *uninitialized_var(prev_alloc_class);
>
> + struct size_class *prev_class = NULL;
>
> Use the fact it's unset below, so set it to NULL here

Yes, You are right. I will change it in next resend.
Thanks for your review.

>
>>
>> size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
>> if (size > ZS_MAX_ALLOC_SIZE)
>> @@ -987,9 +987,8 @@ struct zs_pool *zs_create_pool(gfp_t flags)
>> * previous size_class if possible.
>> */
>> if (i < ZS_SIZE_CLASSES - 1) {
>> - prev_class = pool->size_class[i + 1];
>> - if (can_merge(prev_class, size, pages_per_zspage)) {
>> - pool->size_class[i] = prev_class;
>> + if (can_merge(prev_alloc_class, size, pages_per_zspage)) {
>> + pool->size_class[i] = prev_alloc_class;
>
> simplify more, we can check if this is the first iteration by looking
> at prev_class, e.g.:
>
> 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_alloc_class = class;
>> }
>>
>> pool->flags = flags;
>> --
>> 1.7.9.5
>>
>> --
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