linux-kernel - Re: [PATCH] mm/zsmalloc: avoid duplicate assignment of prev

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Date:	Fri, 21 Nov 2014 13:22:21 +0800
From:	Ganesh Mahendran <opensource.ganesh@...il.com>
To:	Dan Streetman <ddstreet@...e.org>
Cc:	Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Linux-MM <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/zsmalloc: avoid duplicate assignment of prev_class

Hello

2014-11-21 11:22 GMT+08:00 Dan Streetman <ddstreet@...e.org>:
> On Thu, Nov 20, 2014 at 8:08 AM, Mahendran Ganesh
> <opensource.ganesh@...il.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@...il.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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