linux-kernel - Re: [PATCH v2 2/4] zsmalloc: change return value unit of zs_get_total_size

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Date:	Wed, 20 Aug 2014 08:47:48 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Seth Jennings <sjennings@...iantweb.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Jerome Marchand <jmarchan@...hat.com>, juno.choi@....com,
	seungho1.park@....com, Luigi Semenzato <semenzato@...gle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Dan Streetman <ddstreet@...e.org>, ds2horner@...il.com
Subject: Re: [PATCH v2 2/4] zsmalloc: change return value unit of
 zs_get_total_size_bytes

On Tue, Aug 19, 2014 at 10:11:57AM -0500, Seth Jennings wrote:
> On Tue, Aug 19, 2014 at 09:46:28AM -0500, Seth Jennings wrote:
> > On Tue, Aug 19, 2014 at 04:54:45PM +0900, Minchan Kim wrote:
> > > zs_get_total_size_bytes returns a amount of memory zsmalloc
> > > consumed with *byte unit* but zsmalloc operates *page unit*
> > > rather than byte unit so let's change the API so benefit
> > > we could get is that reduce unnecessary overhead
> > > (ie, change page unit with byte unit) in zsmalloc.
> > > 
> > > Now, zswap can rollback to zswap_pool_pages.
> > > Over to zswap guys ;-)
> > 
> > I don't think that's how is it done :-/  Changing the API for a
> > component that has two users, changing one, then saying "hope you guys
> > change your newly broken stuff".
> 
> However, I'll bite on this one :)  Just squash this in so that

Thanks for the eating but it's not what I wanted.
I'd like to leave current semantic of zpool and up to you to roll back
to old time. ;-)

> zpool/zswap aren't broken at any point.
> 
> Dan, care to make sure I didn't miss something?
> 
> Thanks,
> Seth
> 
> diff --git a/mm/zbud.c b/mm/zbud.c
> index a05790b..27a3701 100644
> --- a/mm/zbud.c
> +++ b/mm/zbud.c
> @@ -179,7 +179,7 @@ static void zbud_zpool_unmap(void *pool, unsigned long handle)
>  
>  static u64 zbud_zpool_total_size(void *pool)
>  {
> -	return zbud_get_pool_size(pool) * PAGE_SIZE;
> +	return zbud_get_pool_size(pool);
>  }
>  
>  static struct zpool_driver zbud_zpool_driver = {
> diff --git a/mm/zpool.c b/mm/zpool.c
> index e40612a..d126ebc 100644
> --- a/mm/zpool.c
> +++ b/mm/zpool.c
> @@ -336,9 +336,9 @@ void zpool_unmap_handle(struct zpool *zpool, unsigned long handle)
>   * zpool_get_total_size() - The total size of the pool
>   * @pool	The zpool to check
>   *
> - * This returns the total size in bytes of the pool.
> + * This returns the total size in pages of the pool.
>   *
> - * Returns: Total size of the zpool in bytes.
> + * Returns: Total size of the zpool in pages.
>   */
>  u64 zpool_get_total_size(struct zpool *zpool)
>  {
> diff --git a/mm/zswap.c b/mm/zswap.c
> index ea064c1..124f750 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -45,8 +45,8 @@
>  /*********************************
>  * statistics
>  **********************************/
> -/* Total bytes used by the compressed storage */
> -static u64 zswap_pool_total_size;
> +/* Total pages used by the compressed storage */
> +static u64 zswap_pool_pages;
>  /* The number of compressed pages currently stored in zswap */
>  static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
>  
> @@ -297,7 +297,7 @@ static void zswap_free_entry(struct zswap_entry *entry)
>  	zpool_free(zswap_pool, entry->handle);
>  	zswap_entry_cache_free(entry);
>  	atomic_dec(&zswap_stored_pages);
> -	zswap_pool_total_size = zpool_get_total_size(zswap_pool);
> +	zswap_pool_pages = zpool_get_total_size(zswap_pool);
>  }
>  
>  /* caller must hold the tree lock */
> @@ -414,7 +414,7 @@ cleanup:
>  static bool zswap_is_full(void)
>  {
>  	return totalram_pages * zswap_max_pool_percent / 100 <
> -		DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
> +		zswap_pool_pages;
>  }
>  
>  /*********************************
> @@ -721,7 +721,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
>  
>  	/* update stats */
>  	atomic_inc(&zswap_stored_pages);
> -	zswap_pool_total_size = zpool_get_total_size(zswap_pool);
> +	zswap_pool_pages = zpool_get_total_size(zswap_pool);
>  
>  	return 0;
>  
> @@ -874,8 +874,8 @@ static int __init zswap_debugfs_init(void)
>  			zswap_debugfs_root, &zswap_written_back_pages);
>  	debugfs_create_u64("duplicate_entry", S_IRUGO,
>  			zswap_debugfs_root, &zswap_duplicate_entry);
> -	debugfs_create_u64("pool_total_size", S_IRUGO,
> -			zswap_debugfs_root, &zswap_pool_total_size);
> +	debugfs_create_u64("pool_pages", S_IRUGO,
> +			zswap_debugfs_root, &zswap_pool_pages);
>  	debugfs_create_atomic_t("stored_pages", S_IRUGO,
>  			zswap_debugfs_root, &zswap_stored_pages);
>  
> --
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-- 
Kind regards,
Minchan Kim
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