[PATCH -next v8 0/3] Delay the initialization of zswap

[PATCH -next v8 0/3] Delay the initialization of zswap

[Liu Shixin]

In the initialization of zswap, about 18MB memory will be allocated for
zswap_pool. Since some users may not use zswap, the zswap_pool is wasted.
Save memory by delaying the initialization of zswap until enabled.

v7->v8: Do some cleanup. And remove the second patch in v7 which is unrelated
	to the initialization of zswap.
v6->v7: Add two new patch[1,3] to cleanup the code. And cover zswap_init_*
	parameter by zswap_init_lock to protect against conflicts.
v5->v6: Simplify the code and delete the patches about frontswap suggested
	by Christoph.

Liu Shixin (3):
  mm/zswap: remove zswap_entry_cache_{create,destroy} helper function
  mm/zswap: replace zswap_init_{started/failed} with zswap_init_state
  mm/zswap: delay the initialization of zswap

 mm/zswap.c | 111 ++++++++++++++++++++++++++++++++---------------------
 1 file changed, 68 insertions(+), 43 deletions(-)

-- 
2.25.1

[PATCH -next v8 1/3] mm/zswap: remove zswap_entry_cache_{create,destroy} helper function

[Liu Shixin]

Remove zswap_entry_cache_create and zswap_entry_cache_destroy and use
kmem_cache_* function directly.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 mm/zswap.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 2f0ebd8bc620..6d2b879f091e 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -272,17 +272,6 @@ static void zswap_update_total_size(void)
 **********************************/
 static struct kmem_cache *zswap_entry_cache;
 
-static int __init zswap_entry_cache_create(void)
-{
-	zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
-	return zswap_entry_cache == NULL;
-}
-
-static void __init zswap_entry_cache_destroy(void)
-{
-	kmem_cache_destroy(zswap_entry_cache);
-}
-
 static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
 {
 	struct zswap_entry *entry;
@@ -1489,7 +1478,8 @@ static int __init init_zswap(void)
 
 	zswap_init_started = true;
 
-	if (zswap_entry_cache_create()) {
+	zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
+	if (!zswap_entry_cache) {
 		pr_err("entry cache creation failed\n");
 		goto cache_fail;
 	}
@@ -1538,7 +1528,7 @@ static int __init init_zswap(void)
 hp_fail:
 	cpuhp_remove_state(CPUHP_MM_ZSWP_MEM_PREPARE);
 dstmem_fail:
-	zswap_entry_cache_destroy();
+	kmem_cache_destroy(zswap_entry_cache);
 cache_fail:
 	/* if built-in, we aren't unloaded on failure; don't allow use */
 	zswap_init_failed = true;
-- 
2.25.1

[PATCH -next v8 2/3] mm/zswap: replace zswap_init_{started/failed} with zswap_init_state

[Liu Shixin]

The zswap_init_started variable name has a bit confusing. Actually, there
are three state: uninitialized, initial failed and initial succeed. Add
a new variable zswap_init_state to replace zswap_init_{started/failed}.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
---
 mm/zswap.c | 55 +++++++++++++++++++++++++++++-------------------------
 1 file changed, 30 insertions(+), 25 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 6d2b879f091e..9169c2baee87 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -214,11 +214,13 @@ static DEFINE_SPINLOCK(zswap_pools_lock);
 /* pool counter to provide unique names to zpool */
 static atomic_t zswap_pools_count = ATOMIC_INIT(0);
 
-/* used by param callback function */
-static bool zswap_init_started;
+enum zswap_init_type {
+	ZSWAP_UNINIT,
+	ZSWAP_INIT_SUCCEED,
+	ZSWAP_INIT_FAILED
+};
 
-/* fatal error during init */
-static bool zswap_init_failed;
+static enum zswap_init_type zswap_init_state;
 
 /* init completed, but couldn't create the initial pool */
 static bool zswap_has_pool;
@@ -761,21 +763,22 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
 	char *s = strstrip((char *)val);
 	int ret;
 
-	if (zswap_init_failed) {
+	switch (zswap_init_state) {
+	case ZSWAP_UNINIT:
+		/* if this is load-time (pre-init) param setting,
+		 * don't create a pool; that's done during init.
+		 */
+		return param_set_charp(s, kp);
+	case ZSWAP_INIT_SUCCEED:
+		/* no change required */
+		if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
+			return 0;
+		break;
+	case ZSWAP_INIT_FAILED:
 		pr_err("can't set param, initialization failed\n");
 		return -ENODEV;
 	}
 
-	/* no change required */
-	if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
-		return 0;
-
-	/* 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_charp(s, kp);
-
 	if (!type) {
 		if (!zpool_has_pool(s)) {
 			pr_err("zpool %s not available\n", s);
@@ -864,16 +867,19 @@ static int zswap_zpool_param_set(const char *val,
 static int zswap_enabled_param_set(const char *val,
 				   const struct kernel_param *kp)
 {
-	if (zswap_init_failed) {
+	switch (zswap_init_state) {
+	case ZSWAP_UNINIT:
+		return param_set_bool(val, kp);
+	case ZSWAP_INIT_SUCCEED:
+		if (!zswap_has_pool) {
+			pr_err("can't enable, no pool configured\n");
+			return -ENODEV;
+		} else
+			return param_set_bool(val, kp);
+	case ZSWAP_INIT_FAILED:
 		pr_err("can't enable, initialization failed\n");
 		return -ENODEV;
 	}
-	if (!zswap_has_pool && zswap_init_started) {
-		pr_err("can't enable, no pool configured\n");
-		return -ENODEV;
-	}
-
-	return param_set_bool(val, kp);
 }
 
 /*********************************
@@ -1476,8 +1482,6 @@ static int __init init_zswap(void)
 	struct zswap_pool *pool;
 	int ret;
 
-	zswap_init_started = true;
-
 	zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
 	if (!zswap_entry_cache) {
 		pr_err("entry cache creation failed\n");
@@ -1518,6 +1522,7 @@ static int __init init_zswap(void)
 		goto destroy_wq;
 	if (zswap_debugfs_init())
 		pr_warn("debugfs initialization failed\n");
+	zswap_init_state = ZSWAP_INIT_SUCCEED;
 	return 0;
 
 destroy_wq:
@@ -1531,7 +1536,7 @@ static int __init init_zswap(void)
 	kmem_cache_destroy(zswap_entry_cache);
 cache_fail:
 	/* if built-in, we aren't unloaded on failure; don't allow use */
-	zswap_init_failed = true;
+	zswap_init_state = ZSWAP_INIT_FAILED;
 	zswap_enabled = false;
 	return -ENOMEM;
 }
-- 
2.25.1

Re: [PATCH -next v8 2/3] mm/zswap: replace zswap_init_{started/failed} with zswap_init_state

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH -next v8 3/3] mm/zswap: delay the initialization of zswap

[Liu Shixin]

Since some users may not use zswap, the zswap_pool is wasted. Save memory
by delaying the initialization of zswap until enabled.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
---
 mm/zswap.c | 56 +++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 43 insertions(+), 13 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 9169c2baee87..14db57450bfd 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -81,6 +81,8 @@ static bool zswap_pool_reached_full;
 
 #define ZSWAP_PARAM_UNSET ""
 
+static int zswap_setup(void);
+
 /* Enable/disable zswap */
 static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
 static int zswap_enabled_param_set(const char *,
@@ -222,6 +224,9 @@ enum zswap_init_type {
 
 static enum zswap_init_type zswap_init_state;
 
+/* used to ensure the integrity of initialization */
+static DEFINE_MUTEX(zswap_init_lock);
+
 /* init completed, but couldn't create the initial pool */
 static bool zswap_has_pool;
 
@@ -654,7 +659,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
 	return NULL;
 }
 
-static __init struct zswap_pool *__zswap_pool_create_fallback(void)
+static struct zswap_pool *__zswap_pool_create_fallback(void)
 {
 	bool has_comp, has_zpool;
 
@@ -763,21 +768,28 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
 	char *s = strstrip((char *)val);
 	int ret;
 
+	mutex_lock(&zswap_init_lock);
 	switch (zswap_init_state) {
 	case ZSWAP_UNINIT:
 		/* if this is load-time (pre-init) param setting,
 		 * don't create a pool; that's done during init.
 		 */
-		return param_set_charp(s, kp);
+		ret = param_set_charp(s, kp);
+		mutex_unlock(&zswap_init_lock);
+		return ret;
 	case ZSWAP_INIT_SUCCEED:
 		/* no change required */
-		if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
+		if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool) {
+			mutex_unlock(&zswap_init_lock);
 			return 0;
+		}
 		break;
 	case ZSWAP_INIT_FAILED:
 		pr_err("can't set param, initialization failed\n");
+		mutex_unlock(&zswap_init_lock);
 		return -ENODEV;
 	}
+	mutex_unlock(&zswap_init_lock);
 
 	if (!type) {
 		if (!zpool_has_pool(s)) {
@@ -867,19 +879,30 @@ static int zswap_zpool_param_set(const char *val,
 static int zswap_enabled_param_set(const char *val,
 				   const struct kernel_param *kp)
 {
+	int ret = -ENODEV;
+
+	/*if this is load-time (pre-init) param setting, only set param.*/
+	if (system_state != SYSTEM_RUNNING)
+		return param_set_bool(val, kp);
+
+	mutex_lock(&zswap_init_lock);
 	switch (zswap_init_state) {
 	case ZSWAP_UNINIT:
-		return param_set_bool(val, kp);
+		if (zswap_setup())
+			break;
+		fallthrough;
 	case ZSWAP_INIT_SUCCEED:
-		if (!zswap_has_pool) {
+		if (!zswap_has_pool)
 			pr_err("can't enable, no pool configured\n");
-			return -ENODEV;
-		} else
-			return param_set_bool(val, kp);
+		else
+			ret = param_set_bool(val, kp);
+		break;
 	case ZSWAP_INIT_FAILED:
 		pr_err("can't enable, initialization failed\n");
-		return -ENODEV;
 	}
+	mutex_unlock(&zswap_init_lock);
+
+	return ret;
 }
 
 /*********************************
@@ -1437,7 +1460,7 @@ static const struct frontswap_ops zswap_frontswap_ops = {
 
 static struct dentry *zswap_debugfs_root;
 
-static int __init zswap_debugfs_init(void)
+static int zswap_debugfs_init(void)
 {
 	if (!debugfs_initialized())
 		return -ENODEV;
@@ -1468,7 +1491,7 @@ static int __init zswap_debugfs_init(void)
 	return 0;
 }
 #else
-static int __init zswap_debugfs_init(void)
+static int zswap_debugfs_init(void)
 {
 	return 0;
 }
@@ -1477,7 +1500,7 @@ static int __init zswap_debugfs_init(void)
 /*********************************
 * module init and exit
 **********************************/
-static int __init init_zswap(void)
+static int zswap_setup(void)
 {
 	struct zswap_pool *pool;
 	int ret;
@@ -1540,8 +1563,15 @@ static int __init init_zswap(void)
 	zswap_enabled = false;
 	return -ENOMEM;
 }
+
+static int __init zswap_init(void)
+{
+	if (!zswap_enabled)
+		return 0;
+	return zswap_setup();
+}
 /* must be late so crypto has time to come up */
-late_initcall(init_zswap);
+late_initcall(zswap_init);
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Seth Jennings <sjennings@variantweb.net>");
-- 
2.25.1

Re: [PATCH -next v8 3/3] mm/zswap: delay the initialization of zswap

[Christoph Hellwig]

On Mon, Apr 03, 2023 at 08:13:18PM +0800, Liu Shixin wrote:
> Since some users may not use zswap, the zswap_pool is wasted. Save memory
> by delaying the initialization of zswap until enabled.
> 
> Signed-off-by: Liu Shixin <liushixin2@huawei.com>
> ---
>  mm/zswap.c | 56 +++++++++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 43 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 9169c2baee87..14db57450bfd 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -81,6 +81,8 @@ static bool zswap_pool_reached_full;
>  
>  #define ZSWAP_PARAM_UNSET ""
>  
> +static int zswap_setup(void);
> +
>  /* Enable/disable zswap */
>  static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
>  static int zswap_enabled_param_set(const char *,
> @@ -222,6 +224,9 @@ enum zswap_init_type {
>  
>  static enum zswap_init_type zswap_init_state;
>  
> +/* used to ensure the integrity of initialization */
> +static DEFINE_MUTEX(zswap_init_lock);
> +
>  /* init completed, but couldn't create the initial pool */
>  static bool zswap_has_pool;
>  
> @@ -654,7 +659,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
>  	return NULL;
>  }
>  
> -static __init struct zswap_pool *__zswap_pool_create_fallback(void)
> +static struct zswap_pool *__zswap_pool_create_fallback(void)
>  {
>  	bool has_comp, has_zpool;
>  
> @@ -763,21 +768,28 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
>  	char *s = strstrip((char *)val);
>  	int ret;
>  
> +	mutex_lock(&zswap_init_lock);
>  	switch (zswap_init_state) {
>  	case ZSWAP_UNINIT:
>  		/* if this is load-time (pre-init) param setting,
>  		 * don't create a pool; that's done during init.
>  		 */
> -		return param_set_charp(s, kp);
> +		ret = param_set_charp(s, kp);
> +		mutex_unlock(&zswap_init_lock);
> +		return ret;
>  	case ZSWAP_INIT_SUCCEED:
>  		/* no change required */
> -		if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
> +		if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool) {
> +			mutex_unlock(&zswap_init_lock);
>  			return 0;
> +		}
>  		break;
>  	case ZSWAP_INIT_FAILED:
>  		pr_err("can't set param, initialization failed\n");
> +		mutex_unlock(&zswap_init_lock);
>  		return -ENODEV;
>  	}
> +	mutex_unlock(&zswap_init_lock);

The pattern here looks a bit odd.  Can you split the code that
the ZSWAP_INIT_SUCCEED case falls through into a helper, then just
assign ret inside the switch statement, break out and do a single
unlock and return?

> +	/*if this is load-time (pre-init) param setting, only set param.*/

missing space after the initial and before the last * here.

But except for these nitpicks this version looks good to me now.