linux-kernel - Re: [PATCH 3/5] zswap: runtime enable/disable

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Date:	Tue, 2 Jun 2015 15:11:18 -0500
From:	Seth Jennings <sjennings@...iantweb.net>
To:	Dan Streetman <ddstreet@...e.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] zswap: runtime enable/disable

On Tue, Jun 02, 2015 at 11:11:55AM -0400, Dan Streetman wrote:
> Change the "enabled" parameter to be configurable at runtime.  Remove
> the enabled check from init(), and move it to the frontswap store()
> function; when enabled, pages will be stored, and when disabled, pages
> won't be stored.

I like this one. So much so I wrote it about 2 years ago :)

http://lkml.iu.edu/hypermail/linux/kernel/1307.2/04289.html

It didn't go in though and I forgot about it.

We need to update the documentation too (see my patch).

Thanks,
Seth

> 
> Signed-off-by: Dan Streetman <ddstreet@...e.org>
> ---
>  mm/zswap.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 4249e82..e070b10 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -75,9 +75,10 @@ static u64 zswap_duplicate_entry;
>  /*********************************
>  * tunables
>  **********************************/
> -/* Enable/disable zswap (disabled by default, fixed at boot for now) */
> -static bool zswap_enabled __read_mostly;
> -module_param_named(enabled, zswap_enabled, bool, 0444);
> +
> +/* Enable/disable zswap (disabled by default) */
> +static bool zswap_enabled;
> +module_param_named(enabled, zswap_enabled, bool, 0644);
>  
>  /* Compressor to be used by zswap (fixed at boot for now) */
>  #define ZSWAP_COMPRESSOR_DEFAULT "lzo"
> @@ -648,6 +649,9 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
>  	u8 *src, *dst;
>  	struct zswap_header *zhdr;
>  
> +	if (!zswap_enabled)
> +		return -EPERM;
> +
>  	if (!tree) {
>  		ret = -ENODEV;
>  		goto reject;
> @@ -901,9 +905,6 @@ static int __init init_zswap(void)
>  {
>  	gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN;
>  
> -	if (!zswap_enabled)
> -		return 0;
> -
>  	pr_info("loading zswap\n");
>  
>  	zswap_pool = zpool_create_pool(zswap_zpool_type, "zswap", gfp,
> -- 
> 2.1.0
> 
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