linux-kernel - Re: [PATCH 5/8] mm/zsmalloc: avoid calculate max objects of zspage twice

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Date:	Mon, 4 Jul 2016 09:03:18 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Ganesh Mahendran <opensource.ganesh@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<akpm@...ux-foundation.org>, <ngupta@...are.org>,
	<sergey.senozhatsky.work@...il.com>, <rostedt@...dmis.org>,
	<mingo@...hat.com>
Subject: Re: [PATCH 5/8] mm/zsmalloc: avoid calculate max objects of zspage
 twice

On Fri, Jul 01, 2016 at 02:41:03PM +0800, Ganesh Mahendran wrote:
> Currently, if a class can not be merged, the max objects of zspage
> in that class may be calculated twice.
> 
> This patch calculate max objects of zspage at the begin, and pass
> the value to can_merge() to decide whether the class can be merged.
> 
> Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.com>
> ---
>  mm/zsmalloc.c | 21 ++++++++++-----------
>  1 file changed, 10 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 50283b1..2690914 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1362,16 +1362,14 @@ static void init_zs_size_classes(void)
>  	zs_size_classes = nr;
>  }
>  
> -static bool can_merge(struct size_class *prev, int size, int pages_per_zspage)
> +static bool can_merge(struct size_class *prev, int pages_per_zspage,
> +					int objs_per_zspage)
>  {
> -	if (prev->pages_per_zspage != pages_per_zspage)
> -		return false;
> -
> -	if (prev->objs_per_zspage
> -		!= get_maxobj_per_zspage(size, pages_per_zspage))
> -		return false;
> +	if (prev->pages_per_zspage == pages_per_zspage &&
> +		prev->objs_per_zspage == objs_per_zspage)
> +		return true;
>  
> -	return true;
> +	return false;
>  }
>  
>  static bool zspage_full(struct size_class *class, struct zspage *zspage)
> @@ -2460,6 +2458,7 @@ struct zs_pool *zs_create_pool(const char *name)
>  	for (i = zs_size_classes - 1; i >= 0; i--) {
>  		int size;
>  		int pages_per_zspage;
> +		int objs_per_zspage;
>  		struct size_class *class;
>  		int fullness = 0;
>  
> @@ -2467,6 +2466,7 @@ struct zs_pool *zs_create_pool(const char *name)
>  		if (size > ZS_MAX_ALLOC_SIZE)
>  			size = ZS_MAX_ALLOC_SIZE;
>  		pages_per_zspage = get_pages_per_zspage(size);
> +		objs_per_zspage = get_maxobj_per_zspage(size, pages_per_zspage);

So, user of get_maxobj_per_zspage is only here? If so, let's remove
get_maxobj_per_zspage to prevent misuse in future. Instead, use open code
here.


>  
>  		/*
>  		 * size_class is used for normal zsmalloc operation such
> @@ -2478,7 +2478,7 @@ struct zs_pool *zs_create_pool(const char *name)
>  		 * previous size_class if possible.
>  		 */
>  		if (prev_class) {
> -			if (can_merge(prev_class, size, pages_per_zspage)) {
> +			if (can_merge(prev_class, pages_per_zspage, objs_per_zspage)) {
>  				pool->size_class[i] = prev_class;
>  				continue;
>  			}
> @@ -2491,8 +2491,7 @@ struct zs_pool *zs_create_pool(const char *name)
>  		class->size = size;
>  		class->index = i;
>  		class->pages_per_zspage = pages_per_zspage;
> -		class->objs_per_zspage = get_maxobj_per_zspage(class->size,
> -							class->pages_per_zspage);
> +		class->objs_per_zspage = objs_per_zspage;
>  		spin_lock_init(&class->lock);
>  		pool->size_class[i] = class;
>  		for (fullness = ZS_EMPTY; fullness < NR_ZS_FULLNESS;
> -- 
> 1.9.1
>