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

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Date:   Sat, 21 Jan 2017 17:43:38 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     zhouxianrong@...wei.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, sergey.senozhatsky@...il.com,
        minchan@...nel.org, ngupta@...are.org, Mi.Sophia.Wang@...wei.com,
        zhouxiyu@...wei.com, weidu.du@...wei.com, zhangshiming5@...wei.com,
        won.ho.park@...wei.com
Subject: Re: [PATCH] mm: extend zero pages to same element pages for zram

Hello,

On (01/13/17 16:29), zhouxianrong@...wei.com wrote:
[..]
> --- a/Documentation/ABI/testing/sysfs-block-zram
> +++ b/Documentation/ABI/testing/sysfs-block-zram
> @@ -86,21 +86,21 @@ Description:
>  		ones are sent by filesystem mounted with discard option,
>  		whenever some data blocks are getting discarded.
>  
> -What:		/sys/block/zram<id>/zero_pages
> +What:		/sys/block/zram<id>/same_pages
[..]
> -zero_pages        RO    the number of zero filled pages written to this disk
> +same_pages        RO    the number of same element filled pages written to this disk
[..]
> -	zero_pages
> +	same_pages
>  	num_migrated
> +}

we removed deprecated sysfs attrs. zero_pages does not exist anymore.

>  static size_t zram_get_obj_size(struct zram_meta *meta, u32 index)
>  {
>  	return meta->table[index].value & (BIT(ZRAM_FLAG_SHIFT) - 1);
> @@ -158,31 +169,76 @@ 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 = PAGE_SIZE / sizeof(unsigned long) - 1; i >= 0; i--)
> +			page[i] = value;
> +	}

any particular reason not to use memset() here?
memset() can be faster that that, right?


[..]
>  /* Flags for zram pages (table[page_no].value) */
>  enum zram_pageflags {
> -	/* Page consists entirely of zeros */
> -	ZRAM_ZERO = ZRAM_FLAG_SHIFT,
> +	/* Page consists entirely of same elements */
> +	ZRAM_SAME = ZRAM_FLAG_SHIFT,
>  	ZRAM_ACCESS,	/* page is now accessed */
[..]
> @@ -83,7 +86,7 @@ struct zram_stats {
>  	atomic64_t failed_writes;	/* can happen when memory is too low */
>  	atomic64_t invalid_io;	/* non-page-aligned I/O requests */
>  	atomic64_t notify_free;	/* no. of swap slot free notifications */
> -	atomic64_t zero_pages;		/* no. of zero filled pages */
> +	atomic64_t same_pages;		/* no. of same element filled pages */

not like this rename is particularity important, but ok. works for me.

	-ss