[-next,v6,2/2] mm/zswap: delay the initializaton of zswap

  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 | 51 +++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 41 insertions(+), 10 deletions(-)
  

On Wed, Mar 22, 2023 at 10:30 AM Liu Shixin <liushixin2@huawei.com> wrote:
>
> Since some users may not use zswap, the zswap_pool is wasted. Save memory
> by delaying the initialization of zswap until enabled.

To be honest, I'm not a huge fan of this. Would enabling zswap module
build instead solve your problem?

~Vitaly

> Signed-off-by: Liu Shixin <liushixin2@huawei.com>
> ---
>  mm/zswap.c | 51 +++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 41 insertions(+), 10 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 09fa956920fa..3aed3b26524a 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 *,
> @@ -220,6 +222,9 @@ static bool zswap_init_started;
>  /* fatal error during init */
>  static bool zswap_init_failed;
>
> +/* 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;
>
> @@ -272,13 +277,13 @@ static void zswap_update_total_size(void)
>  **********************************/
>  static struct kmem_cache *zswap_entry_cache;
>
> -static int __init zswap_entry_cache_create(void)
> +static int 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)
> +static void zswap_entry_cache_destroy(void)
>  {
>         kmem_cache_destroy(zswap_entry_cache);
>  }
> @@ -663,7 +668,7 @@ 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;
>
> @@ -784,8 +789,15 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
>         /* 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 (!zswap_init_started) {
> +               mutex_lock(&zswap_init_lock);
> +               if (!zswap_init_started) {
> +                       ret = param_set_charp(s, kp);
> +                       mutex_unlock(&zswap_init_lock);
> +                       return ret;
> +               }
> +               mutex_unlock(&zswap_init_lock);
> +       }
>
>         if (!type) {
>                 if (!zpool_has_pool(s)) {
> @@ -884,6 +896,15 @@ static int zswap_enabled_param_set(const char *val,
>         if (res == *(bool *)kp->arg)
>                 return 0;
>
> +       if (!zswap_init_started && (system_state == SYSTEM_RUNNING)) {
> +               mutex_lock(&zswap_init_lock);
> +               if (zswap_setup()) {
> +                       mutex_unlock(&zswap_init_lock);
> +                       return -ENODEV;
> +               }
> +               mutex_unlock(&zswap_init_lock);
> +       }
> +
>         if (zswap_init_failed) {
>                 pr_err("can't enable, initialization failed\n");
>                 return -ENODEV;
> @@ -1451,7 +1472,7 @@ 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;
> @@ -1482,7 +1503,7 @@ 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;
>  }
> @@ -1491,12 +1512,13 @@ 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;
>
> -       zswap_init_started = true;
> +       if (zswap_init_started)
> +               return 0;
>
>         if (zswap_entry_cache_create()) {
>                 pr_err("entry cache creation failed\n");
> @@ -1537,6 +1559,7 @@ static int __init init_zswap(void)
>                 goto destroy_wq;
>         if (zswap_debugfs_init())
>                 pr_warn("debugfs initialization failed\n");
> +       zswap_init_started = true;
>         return 0;
>
>  destroy_wq:
> @@ -1551,11 +1574,19 @@ static int __init init_zswap(void)
>  cache_fail:
>         /* if built-in, we aren't unloaded on failure; don't allow use */
>         zswap_init_failed = true;
> +       zswap_init_started = true;
>         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
>
  

On Wed, Mar 22, 2023 at 06:17:12PM +0100, Vitaly Wool wrote:
> On Wed, Mar 22, 2023 at 10:30 AM Liu Shixin <liushixin2@huawei.com> wrote:
> >
> > Since some users may not use zswap, the zswap_pool is wasted. Save memory
> > by delaying the initialization of zswap until enabled.
> 
> To be honest, I'm not a huge fan of this. Would enabling zswap module
> build instead solve your problem?

making zswap build modular would be a mess.  It is core MM infrastructure
and now we'd need to start dealing with adding and removing it at
runtime as well as module refcounting.
  

On Wed, Mar 22, 2023 at 06:20:06PM +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 | 51 +++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 41 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 09fa956920fa..3aed3b26524a 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 *,
> @@ -220,6 +222,9 @@ static bool zswap_init_started;
>  /* fatal error during init */
>  static bool zswap_init_failed;
>  
> +/* 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;
>  
> @@ -272,13 +277,13 @@ static void zswap_update_total_size(void)
>  **********************************/
>  static struct kmem_cache *zswap_entry_cache;
>  
> -static int __init zswap_entry_cache_create(void)
> +static int zswap_entry_cache_create(void)
>  {
>  	zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
>  	return zswap_entry_cache == NULL;
>  }

Please add a cleanup patch to remove this helper first, it just
massivel confuses the reader.

> -static void __init zswap_entry_cache_destroy(void)
> +static void zswap_entry_cache_destroy(void)
>  {
>  	kmem_cache_destroy(zswap_entry_cache);
>  }

Same here.

> @@ -663,7 +668,7 @@ 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;
>  
> @@ -784,8 +789,15 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
>  	/* 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 (!zswap_init_started) {
> +		mutex_lock(&zswap_init_lock);
> +		if (!zswap_init_started) {
> +			ret = param_set_charp(s, kp);
> +			mutex_unlock(&zswap_init_lock);
> +			return ret;
> +		}
> +		mutex_unlock(&zswap_init_lock);
> +	}

Just take the lock around the whole function.  No need to micro-optimize
setting a kernel paramter.

> @@ -884,6 +896,15 @@ static int zswap_enabled_param_set(const char *val,
>  	if (res == *(bool *)kp->arg)
>  		return 0;
>  
> +	if (!zswap_init_started && (system_state == SYSTEM_RUNNING)) {

No need for the inner braces.  But directly looking at
SYSTEM_RUNNING, especially without a comment is a bit of a mess.
Is there any better way to deal with this?

Also the zswap_init_started variable name has always been a bit
confusing.  If everything around it takes zswap_init_lock now,
it can be replaced with a check for successful zswap initialization
as all the initializtion is covered by the lock.  That would really
help to clean up the code.

> +static int zswap_debugfs_init(void)
>  {
>  	if (!debugfs_initialized())
>  		return -ENODEV;
> @@ -1482,7 +1503,7 @@ static int __init zswap_debugfs_init(void)
>  	return 0;
>  }
>  #else
> -static int __init zswap_debugfs_init(void)
> +static int zswap_debugfs_init(void)

Is there any reason to not just always initialize debugfs and
only defer the expensive allocations?
  

On 2023/3/23 16:04, Christoph Hellwig wrote:
> On Wed, Mar 22, 2023 at 06:20:06PM +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 | 51 +++++++++++++++++++++++++++++++++++++++++----------
>>  1 file changed, 41 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 09fa956920fa..3aed3b26524a 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 *,
>> @@ -220,6 +222,9 @@ static bool zswap_init_started;
>>  /* fatal error during init */
>>  static bool zswap_init_failed;
>>  
>> +/* 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;
>>  
>> @@ -272,13 +277,13 @@ static void zswap_update_total_size(void)
>>  **********************************/
>>  static struct kmem_cache *zswap_entry_cache;
>>  
>> -static int __init zswap_entry_cache_create(void)
>> +static int zswap_entry_cache_create(void)
>>  {
>>  	zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
>>  	return zswap_entry_cache == NULL;
>>  }
> Please add a cleanup patch to remove this helper first, it just
> massivel confuses the reader.
I will, thanks.
>
>> -static void __init zswap_entry_cache_destroy(void)
>> +static void zswap_entry_cache_destroy(void)
>>  {
>>  	kmem_cache_destroy(zswap_entry_cache);
>>  }
> Same here.
>
>> @@ -663,7 +668,7 @@ 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;
>>  
>> @@ -784,8 +789,15 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
>>  	/* 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 (!zswap_init_started) {
>> +		mutex_lock(&zswap_init_lock);
>> +		if (!zswap_init_started) {
>> +			ret = param_set_charp(s, kp);
>> +			mutex_unlock(&zswap_init_lock);
>> +			return ret;
>> +		}
>> +		mutex_unlock(&zswap_init_lock);
>> +	}
> Just take the lock around the whole function.  No need to micro-optimize
> setting a kernel paramter.
I will, thanks.
>
>> @@ -884,6 +896,15 @@ static int zswap_enabled_param_set(const char *val,
>>  	if (res == *(bool *)kp->arg)
>>  		return 0;
>>  
>> +	if (!zswap_init_started && (system_state == SYSTEM_RUNNING)) {
> No need for the inner braces.  But directly looking at
> SYSTEM_RUNNING, especially without a comment is a bit of a mess.
> Is there any better way to deal with this?
I have no idea about better way.
>
> Also the zswap_init_started variable name has always been a bit
> confusing.  If everything around it takes zswap_init_lock now,
> it can be replaced with a check for successful zswap initialization
> as all the initializtion is covered by the lock.  That would really
> help to clean up the code.
I will, thanks.
>
>> +static int zswap_debugfs_init(void)
>>  {
>>  	if (!debugfs_initialized())
>>  		return -ENODEV;
>> @@ -1482,7 +1503,7 @@ static int __init zswap_debugfs_init(void)
>>  	return 0;
>>  }
>>  #else
>> -static int __init zswap_debugfs_init(void)
>> +static int zswap_debugfs_init(void)
> Is there any reason to not just always initialize debugfs and
> only defer the expensive allocations?
It seems there is no need to initialize debugfs if zswap is not used.

>
> .
>
  

On Thu, Mar 23, 2023 at 8:59 AM Christoph Hellwig <hch@lst.de> wrote:
>
> On Wed, Mar 22, 2023 at 06:17:12PM +0100, Vitaly Wool wrote:
> > On Wed, Mar 22, 2023 at 10:30 AM Liu Shixin <liushixin2@huawei.com> wrote:
> > >
> > > Since some users may not use zswap, the zswap_pool is wasted. Save memory
> > > by delaying the initialization of zswap until enabled.
> >
> > To be honest, I'm not a huge fan of this. Would enabling zswap module
> > build instead solve your problem?
>
> making zswap build modular would be a mess.  It is core MM infrastructure
> and now we'd need to start dealing with adding and removing it at
> runtime as well as module refcounting.

Since when is it a core MM infrastructure? It is basically just a
frontswap frontend.

~Vitaly