Re: [PATCH 3/3] zswap: change zpool/compressor at runtime

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

Hi,

On (08/05/15 09:46), Dan Streetman wrote:
> Update the zpool and compressor parameters to be changeable at runtime.
> When changed, a new pool is created with the requested zpool/compressor,
> and added as the current pool at the front of the pool list.  Previous
> pools remain in the list only to remove existing compressed pages from.
> The old pool(s) are removed once they become empty.
> 

Sorry, just curious, is this functionality/complication really
necessary? How often do you expect people to do that? The way I
see it -- a static configuration works just fine: boot, test,
re-configure, boot test; compare the results and done.

	-ss

> Signed-off-by: Dan Streetman <ddstreet@ieee.org>
> ---
>  mm/zswap.c | 135 +++++++++++++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 122 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index f8fcd7e..3eaff21 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -80,23 +80,39 @@ static u64 zswap_duplicate_entry;
>  static bool zswap_enabled;
>  module_param_named(enabled, zswap_enabled, bool, 0644);
>  
> -/* Compressor to be used by zswap (fixed at boot for now) */
> +/* Crypto compressor to use */
>  #define ZSWAP_COMPRESSOR_DEFAULT "lzo"
> -static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
> -module_param_named(compressor, zswap_compressor, charp, 0444);
> -
> -/* The maximum percentage of memory that the compressed pool can occupy */
> -static unsigned int zswap_max_pool_percent = 20;
> -module_param_named(max_pool_percent,
> -			zswap_max_pool_percent, uint, 0644);
> +static char zswap_compressor[CRYPTO_MAX_ALG_NAME] = ZSWAP_COMPRESSOR_DEFAULT;
> +static struct kparam_string zswap_compressor_kparam = {
> +	.string =	zswap_compressor,
> +	.maxlen =	sizeof(zswap_compressor),
> +};
> +static int zswap_compressor_param_set(const char *,
> +				      const struct kernel_param *);
> +static struct kernel_param_ops zswap_compressor_param_ops = {
> +	.set =		zswap_compressor_param_set,
> +	.get =		param_get_string,
> +};
> +module_param_cb(compressor, &zswap_compressor_param_ops,
> +		&zswap_compressor_kparam, 0644);
>  
> -/* Compressed storage to use */
> +/* Compressed storage zpool to use */
>  #define ZSWAP_ZPOOL_DEFAULT "zbud"
> -static char *zswap_zpool_type = ZSWAP_ZPOOL_DEFAULT;
> -module_param_named(zpool, zswap_zpool_type, charp, 0444);
> +static char zswap_zpool_type[32 /* arbitrary */] = ZSWAP_ZPOOL_DEFAULT;
> +static struct kparam_string zswap_zpool_kparam = {
> +	.string =	zswap_zpool_type,
> +	.maxlen =	sizeof(zswap_zpool_type),
> +};
> +static int zswap_zpool_param_set(const char *, const struct kernel_param *);
> +static struct kernel_param_ops zswap_zpool_param_ops = {
> +	.set =	zswap_zpool_param_set,
> +	.get =	param_get_string,
> +};
> +module_param_cb(zpool, &zswap_zpool_param_ops, &zswap_zpool_kparam, 0644);
>  
> -/* zpool is shared by all of zswap backend  */
> -static struct zpool *zswap_pool;
> +/* The maximum percentage of memory that the compressed pool can occupy */
> +static unsigned int zswap_max_pool_percent = 20;
> +module_param_named(max_pool_percent, zswap_max_pool_percent, uint, 0644);
>  
>  /*********************************
>  * data structures
> @@ -161,6 +177,9 @@ static LIST_HEAD(zswap_pools);
>  /* protects zswap_pools list modification */
>  static DEFINE_SPINLOCK(zswap_pools_lock);
>  
> +/* used by param callback function */
> +static bool zswap_init_started;
> +
>  /*********************************
>  * helpers and fwd declarations
>  **********************************/
> @@ -661,6 +680,94 @@ static void zswap_pool_put(struct zswap_pool *pool)
>  	kref_put(&pool->kref, __zswap_pool_empty);
>  }
>  
> +/*********************************
> +* param callbacks
> +**********************************/
> +
> +static int __zswap_param_set(const char *val, const struct kernel_param *kp,
> +			     char *type, char *compressor)
> +{
> +	struct zswap_pool *pool, *put_pool = NULL;
> +	char str[kp->str->maxlen], *s;
> +	int ret;
> +
> +	strlcpy(str, val, kp->str->maxlen);
> +	s = strim(str);
> +
> +	/* if this is load-time (pre-init) param setting,
> +	 * don't create a pool; that's done during init.
> +	 */
> +	if (!zswap_init_started)
> +		return param_set_copystring(s, kp);
> +
> +	/* no change required */
> +	if (!strncmp(kp->str->string, s, kp->str->maxlen))
> +		return 0;
> +
> +	if (!type) {
> +		type = s;
> +		if (!zpool_has_pool(type)) {
> +			pr_err("zpool %s not available\n", type);
> +			return -ENOENT;
> +		}
> +	} else if (!compressor) {
> +		compressor = s;
> +		if (!crypto_has_comp(compressor, 0, 0)) {
> +			pr_err("compressor %s not available\n", compressor);
> +			return -ENOENT;
> +		}
> +	}
> +
> +	spin_lock(&zswap_pools_lock);
> +
> +	pool = zswap_pool_find_get(type, compressor);
> +	if (pool) {
> +		zswap_pool_debug("using existing", pool);
> +		list_del_rcu(&pool->list);
> +	} else {
> +		spin_unlock(&zswap_pools_lock);
> +		pool = zswap_pool_create(type, compressor);
> +		spin_lock(&zswap_pools_lock);
> +	}
> +
> +	if (pool)
> +		ret = param_set_copystring(s, kp);
> +	else
> +		ret = -EINVAL;
> +
> +	if (!ret) {
> +		put_pool = zswap_pool_current();
> +		list_add_rcu(&pool->list, &zswap_pools);
> +	} else if (pool) {
> +		/* add the possibly pre-existing pool to the end of the pools
> +		 * list; if it's new (and empty) then it'll be removed and
> +		 * destroyed by the put after we drop the lock
> +		 */
> +		list_add_tail_rcu(&pool->list, &zswap_pools);
> +		put_pool = pool;
> +	}
> +
> +	spin_unlock(&zswap_pools_lock);
> +
> +	/* drop the ref from either the old current pool,
> +	 * or the new pool we failed to add
> +	 */
> +	if (put_pool)
> +		zswap_pool_put(put_pool);
> +
> +	return ret;
> +}
> +
> +static int zswap_compressor_param_set(const char *val,
> +				      const struct kernel_param *kp)
> +{
> +	return __zswap_param_set(val, kp, zswap_zpool_type, NULL);
> +}
> +
> +static int zswap_zpool_param_set(const char *val,
> +				 const struct kernel_param *kp)
> +{
> +	return __zswap_param_set(val, kp, NULL, zswap_compressor);
>  }
>  
>  /*********************************
> @@ -1116,6 +1223,8 @@ static int __init init_zswap(void)
>  {
>  	struct zswap_pool *pool;
>  
> +	zswap_init_started = true;
> +
>  	if (zswap_entry_cache_create()) {
>  		pr_err("entry cache creation failed\n");
>  		goto cache_fail;
> -- 
> 2.1.0
> 
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