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SubjectRe: [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@linux-foundation.org>
> Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
> Cc: Konrad Rzeszutek Wilk <konrad@darnok.org>
> Signed-off-by: Minchan Kim <minchan@kernel.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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