linux-kernel - Re: [PATCH 2/4] zsmalloc: add single-page object fastpath in unmap

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Date:	Tue, 10 Jul 2012 11:25:45 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] zsmalloc: add single-page object fastpath in unmap

On 07/03/2012 06:15 AM, Seth Jennings wrote:
> Improve zs_unmap_object() performance by adding a fast path for
> objects that don't span pages.
> 
> Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> ---
>  drivers/staging/zsmalloc/zsmalloc-main.c |   15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
> index a7a6f22..4942d41 100644
> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
> @@ -774,6 +774,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle)
>  	}
>  
>  	zs_copy_map_object(area->vm_buf, page, off, class->size);
> +	area->vm_addr = NULL;
>  	return area->vm_buf;
>  }
>  EXPORT_SYMBOL_GPL(zs_map_object);
> @@ -788,6 +789,14 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>  	struct size_class *class;
>  	struct mapping_area *area;
>  
> +	area = &__get_cpu_var(zs_map_area);
> +	if (area->vm_addr) {
> +		/* single-page object fastpath */
> +		kunmap_atomic(area->vm_addr);
> +		put_cpu_var(zs_map_area);
> +		return;
> +	}
> +

Please locate this after below BUG_ON.
The BUG check is still effective regardless of your fast path patch.

>  	BUG_ON(!handle);
>  
>  	obj_handle_to_location(handle, &page, &obj_idx);
> @@ -795,11 +804,7 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>  	class = &pool->size_class[class_idx];
>  	off = obj_idx_to_offset(page, obj_idx, class->size);
>  
> -	area = &__get_cpu_var(zs_map_area);
> -	if (off + class->size <= PAGE_SIZE)
> -		kunmap_atomic(area->vm_addr);
> -	else
> -		zs_copy_unmap_object(area->vm_buf, page, off, class->size);
> +	zs_copy_unmap_object(area->vm_buf, page, off, class->size);
>  	put_cpu_var(zs_map_area);
>  }
>  EXPORT_SYMBOL_GPL(zs_unmap_object);
> 


-- 
Kind regards,
Minchan Kim


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