linux-kernel - Re: [PATCH] zsmalloc: Add Kconfig for enabling PTE method

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Date:	Mon, 4 Feb 2013 10:51:46 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Minchan Kim <minchan@...nel.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>
Subject: Re: [PATCH] zsmalloc: Add Kconfig for enabling PTE method

On Mon, Feb 04, 2013 at 09:23:41AM +0900, Minchan Kim wrote:
> Zsmalloc has two methods 1) copy-based and 2) pte based to access
> allocations that span two pages.
> You can see history why we supported two approach from [1].
> 
> But it was bad choice that adding hard coding to select architecture
> which want to use pte based method. This patch removed it and adds
> new Kconfig to select the approach.
> 
> This patch is based on next-20130202.
> 
> [1] https://lkml.org/lkml/2012/7/11/58
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> Cc: Nitin Gupta <ngupta@...are.org>
> Cc: Dan Magenheimer <dan.magenheimer@...cle.com>
> Cc: Konrad Rzeszutek Wilk <konrad@...nok.org>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  drivers/staging/zsmalloc/Kconfig         |   12 ++++++++++++
>  drivers/staging/zsmalloc/zsmalloc-main.c |   11 -----------
>  2 files changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/staging/zsmalloc/Kconfig b/drivers/staging/zsmalloc/Kconfig
> index 9084565..2359123 100644
> --- a/drivers/staging/zsmalloc/Kconfig
> +++ b/drivers/staging/zsmalloc/Kconfig
> @@ -8,3 +8,15 @@ config ZSMALLOC
>  	  non-standard allocator interface where a handle, not a pointer, is
>  	  returned by an alloc().  This handle must be mapped in order to
>  	  access the allocated space.
> +
> +config ZSMALLOC_PGTABLE_MAPPING
> +        bool "Use page table mapping to access allocations that span two pages"
> +        depends on ZSMALLOC
> +        default n
> +        help
> +	  By default, zsmalloc uses a copy-based object mapping method to access
> +	  allocations that span two pages. However, if a particular architecture
> +	  performs VM mapping faster than copying, then you should select this.
> +	  This causes zsmalloc to use page table mapping rather than copying
> +	  for object mapping. You can check speed with zsmalloc benchmark[1].
> +	  [1] https://github.com/spartacus06/zsmalloc
> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
> index 06f73a9..b161ca1 100644
> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
> @@ -218,17 +218,6 @@ struct zs_pool {
>  #define CLASS_IDX_MASK	((1 << CLASS_IDX_BITS) - 1)
>  #define FULLNESS_MASK	((1 << FULLNESS_BITS) - 1)
>  
> -/*
> - * By default, zsmalloc uses a copy-based object mapping method to access
> - * allocations that span two pages. However, if a particular architecture
> - * performs VM mapping faster than copying, then it should be added here
> - * so that USE_PGTABLE_MAPPING is defined. This causes zsmalloc to use
> - * page table mapping rather than copying for object mapping.
> -*/
> -#if defined(CONFIG_ARM)
> -#define USE_PGTABLE_MAPPING
> -#endif

Did you test this?  I don't see the new config value you added actually
do anything in this code.  Also, if I select it incorrectly on ARM, or
or other platforms, what is keeping this from doing bad things?

thanks,

greg k-h
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