Message-ID: <CAM4kBBKOVb9DFSaw6NX3zfN_RqemR5J0HvWHhGiEToRf7e-LUA@mail.gmail.com>
Date:   Sun, 28 Aug 2022 22:45:22 +0200
From:   Vitaly Wool <vitaly.wool@...sulko.com>
To:     Liu Shixin <liushixin2@...wei.com>
Cc:     Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Christoph Hellwig <hch@....de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH -next v3 4/5] mm/zswap: delay the initializaton of zswap
 until the first enablement

On Sat, Aug 27, 2022 at 12:12 PM Liu Shixin <liushixin2@...wei.com> wrote:
>
> In the initialization of zswap, about 18MB memory will be allocated for
> zswap_pool in my machine. Since not all users use zswap, the memory may be
> wasted. Save the memory for these users by delaying the initialization of
> zswap to first enablement.
>
> Signed-off-by: Liu Shixin <liushixin2@...wei.com>

Reviewed-by: Vitaly Wool <vitaly.wool@...sulko.com>

> ---
>  mm/zswap.c | 50 ++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 40 insertions(+), 10 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 84e38300f571..4c476c463035 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 +222,8 @@ static atomic_t zswap_pools_count = ATOMIC_INIT(0);
>
>  /* init state */
>  static int 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;
> @@ -273,13 +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);
>  }
> @@ -664,7 +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;
>
> @@ -782,11 +786,17 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp,
>         if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
>                 return 0;
>
> -       /* if this is load-time (pre-init) param setting,
> +       /*
> +        * if zswap has not been initialized,
>          * don't create a pool; that's done during init.
>          */
> -       if (zswap_init_state == ZSWAP_UNINIT)
> -               return param_set_charp(s, kp);
> +       mutex_lock(&zswap_init_lock);
> +       if (zswap_init_state == ZSWAP_UNINIT) {
> +               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)) {
> @@ -876,6 +886,14 @@ static int zswap_zpool_param_set(const char *val,
>  static int zswap_enabled_param_set(const char *val,
>                                    const struct kernel_param *kp)
>  {
> +       if (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_state == ZSWAP_INIT_FAILED) {
>                 pr_err("can't enable, initialization failed\n");
>                 return -ENODEV;
> @@ -1432,7 +1450,7 @@ 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;
> @@ -1463,7 +1481,7 @@ 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;
>  }
> @@ -1472,11 +1490,14 @@ 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;
>
> +       if (zswap_init_state != ZSWAP_UNINIT)
> +               return 0;
> +
>         if (zswap_entry_cache_create()) {
>                 pr_err("entry cache creation failed\n");
>                 goto cache_fail;
> @@ -1534,8 +1555,17 @@ static int __init init_zswap(void)
>         zswap_enabled = false;
>         return -ENOMEM;
>  }
> +
> +static int __init zswap_init(void)
> +{
> +       /* skip init if zswap is disabled when system startup */
> +       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@...iantweb.net>");
> --
> 2.25.1
>

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