Re: [PATCH v6 6/7] zsmalloc: account the number of compacted pages

[Minchan Kim <minchan@kernel.org>]

On Tue, Jul 07, 2015 at 08:57:00PM +0900, Sergey Senozhatsky wrote:
> Compaction returns back to zram the number of migrated objects,
> which is quite uninformative -- we have objects of different
> sizes so user space cannot obtain any valuable data from that
> number. Change compaction to operate in terms of pages and
> return back to compaction issuer the number of pages that
> were freed during compaction. So from now on we will export
> more meaningful value in zram<id>/mm_stat -- the number of freed
> (compacted) pages.
> 
> This requires:
> (a) a rename of `num_migrated' to 'pages_compacted'
> (b) a internal API change -- return first_page's fullness_group
> from putback_zspage(), so we know when putback_zspage() did
> free_zspage(). It helps us to account compaction stats correctly.
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>

A nit below.

> ---
>  Documentation/blockdev/zram.txt |  3 ++-
>  drivers/block/zram/zram_drv.c   |  2 +-
>  include/linux/zsmalloc.h        |  4 ++--
>  mm/zsmalloc.c                   | 27 +++++++++++++++++----------
>  4 files changed, 22 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
> index c4de576..62435bb 100644
> --- a/Documentation/blockdev/zram.txt
> +++ b/Documentation/blockdev/zram.txt
> @@ -144,7 +144,8 @@ mem_used_max      RW    the maximum amount memory zram have consumed to
>                          store compressed data
>  mem_limit         RW    the maximum amount of memory ZRAM can use to store
>                          the compressed data
> -num_migrated      RO    the number of objects migrated migrated by compaction
> +pages_compacted   RO    the number of pages freed during compaction
> +                        (available only via zram<id>/mm_stat node)
>  compact           WO    trigger memory compaction
>  
>  WARNING
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index aa22fe07..1bcbc19 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -448,7 +448,7 @@ static ssize_t mm_stat_show(struct device *dev,
>  			zram->limit_pages << PAGE_SHIFT,
>  			max_used << PAGE_SHIFT,
>  			(u64)atomic64_read(&zram->stats.zero_pages),
> -			pool_stats.num_migrated);
> +			pool_stats.pages_compacted);
>  	up_read(&zram->init_lock);
>  
>  	return ret;
> diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
> index 9340fce..cda4ad4 100644
> --- a/include/linux/zsmalloc.h
> +++ b/include/linux/zsmalloc.h
> @@ -35,8 +35,8 @@ enum zs_mapmode {
>  };
>  
>  struct zs_pool_stats {
> -	/* How many objects were migrated */
> -	u64		num_migrated;
> +	/* How many pages were migrated (freed) */
> +	u64		pages_compacted;

Hmm, if we account it as page unit, unsigned long is enough for 32bit.

>  };
>  
>  struct zs_pool;
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index db3cb2d..13f2c4a 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1589,8 +1589,6 @@ struct zs_compact_control {
>  	 /* Starting object index within @s_page which used for live object
>  	  * in the subpage. */
>  	int index;
> -	/* How many of objects were migrated */
> -	int nr_migrated;
>  };
>  
>  static int migrate_zspage(struct zs_pool *pool, struct size_class *class,
> @@ -1627,7 +1625,6 @@ static int migrate_zspage(struct zs_pool *pool, struct size_class *class,
>  		record_obj(handle, free_obj);
>  		unpin_tag(handle);
>  		obj_free(pool, class, used_obj);
> -		cc->nr_migrated++;
>  	}
>  
>  	/* Remember last position in this iteration */
> @@ -1653,8 +1650,17 @@ static struct page *isolate_target_page(struct size_class *class)
>  	return page;
>  }
>  
> -static void putback_zspage(struct zs_pool *pool, struct size_class *class,
> -				struct page *first_page)
> +/*
> + * putback_zspage - add @first_page into right class's fullness list
> + * @pool: target pool
> + * @class: destination class
> + * @first_page: target page
> + *
> + * Return @fist_page's fullness_group
> + */
> +static enum fullness_group putback_zspage(struct zs_pool *pool,
> +			struct size_class *class,
> +			struct page *first_page)
>  {
>  	enum fullness_group fullness;
>  
> @@ -1672,6 +1678,8 @@ static void putback_zspage(struct zs_pool *pool, struct size_class *class,
>  
>  		free_zspage(first_page);
>  	}
> +
> +	return fullness;
>  }
>  
>  static struct page *isolate_source_page(struct size_class *class)
> @@ -1713,7 +1721,6 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
>  	struct page *src_page;
>  	struct page *dst_page = NULL;
>  
> -	cc.nr_migrated = 0;
>  	spin_lock(&class->lock);
>  	while ((src_page = isolate_source_page(class))) {
>  
> @@ -1742,7 +1749,9 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
>  			break;
>  
>  		putback_zspage(pool, class, dst_page);
> -		putback_zspage(pool, class, src_page);
> +		if (putback_zspage(pool, class, src_page) == ZS_EMPTY)
> +			pool->stats.pages_compacted +=
> +				get_pages_per_zspage(class->size);
>  		spin_unlock(&class->lock);
>  		cond_resched();
>  		spin_lock(&class->lock);
> @@ -1751,8 +1760,6 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
>  	if (src_page)
>  		putback_zspage(pool, class, src_page);
>  
> -	pool->stats.num_migrated += cc.nr_migrated;
> -
>  	spin_unlock(&class->lock);
>  }
>  
> @@ -1770,7 +1777,7 @@ unsigned long zs_compact(struct zs_pool *pool)
>  		__zs_compact(pool, class);
>  	}
>  
> -	return pool->stats.num_migrated;
> +	return pool->stats.pages_compacted;
>  }
>  EXPORT_SYMBOL_GPL(zs_compact);
>  
> -- 
> 2.4.5
> 

-- 
Kind regards,
Minchan Kim

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