Re: [PATCH] mm: extend zero pages to same element pages for zram

[Minchan Kim]

Hi zhouxianrong,

On Fri, Feb 03, 2017 at 04:42:27PM +0800, zhouxianrong@xxxxxxxxxx wrote:
> From: zhouxianrong <zhouxianrong@xxxxxxxxxx>
> 
> test result as listed below:
> 
> zero   pattern_char pattern_short pattern_int pattern_long total   (unit)
> 162989 14454        3534          23516       2769         3294399 (page)
> 
> statistics for the result:
> 
>         zero  pattern_char  pattern_short  pattern_int  pattern_long
> AVERAGE 0.745696298 0.085937175 0.015957701 0.131874915 0.020533911
> STDEV   0.035623777 0.016892402 0.004454534 0.021657123 0.019420072
> MAX     0.973813421 0.222222222 0.021409518 0.211812245 0.176512625
> MIN     0.645431905 0.004634398 0           0           0

The description in old version was better for justifying same page merging
feature.

> 
> Signed-off-by: zhouxianrong <zhouxianrong@xxxxxxxxxx>
> ---
>  drivers/block/zram/zram_drv.c |  124 +++++++++++++++++++++++++++++++----------
>  drivers/block/zram/zram_drv.h |   11 ++--
>  2 files changed, 103 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index e5ab7d9..6a8c9c5 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -95,6 +95,17 @@ static void zram_clear_flag(struct zram_meta *meta, u32 index,
>  	meta->table[index].value &= ~BIT(flag);
>  }
>  
> +static inline void zram_set_element(struct zram_meta *meta, u32 index,
> +			unsigned long element)
> +{
> +	meta->table[index].element = element;
> +}
> +
> +static inline void zram_clear_element(struct zram_meta *meta, u32 index)
> +{
> +	meta->table[index].element = 0;
> +}
> +
>  static size_t zram_get_obj_size(struct zram_meta *meta, u32 index)
>  {
>  	return meta->table[index].value & (BIT(ZRAM_FLAG_SHIFT) - 1);
> @@ -167,31 +178,78 @@ static inline void update_used_max(struct zram *zram,
>  	} while (old_max != cur_max);
>  }
>  
> -static bool page_zero_filled(void *ptr)
> +static inline void zram_fill_page(char *ptr, unsigned long value)
> +{
> +	int i;
> +	unsigned long *page = (unsigned long *)ptr;
> +
> +	if (likely(value == 0)) {
> +		clear_page(ptr);
> +	} else {
> +		for (i = 0; i < PAGE_SIZE / sizeof(*page); i++)
> +			page[i] = value;
> +	}
> +}
> +
> +static inline void zram_fill_page_partial(char *ptr, unsigned int size,
> +		unsigned long value)
> +{
> +	int i;
> +	unsigned long *page;
> +
> +	if (likely(value == 0)) {
> +		memset(ptr, 0, size);
> +		return;
> +	}
> +
> +	i = ((unsigned long)ptr) % sizeof(*page);
> +	if (i) {
> +		while (i < sizeof(*page)) {
> +			*ptr++ = (value >> (i * 8)) & 0xff;
> +			--size;
> +			++i;
> +		}
> +	}
> +

I don't think we need this part because block layer works with sector
size or multiple times of it so it must be aligned unsigned long.