Re: [PATCH 11/20] mm: zswap: function ordering: pool refcounting

[Nhat Pham <nphamcs@gmail.com>]

On Mon, Jan 29, 2024 at 5:42 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> Move pool refcounting functions into the pool section. First the
> destroy functions, then the get and put which uses them.
>
> __zswap_pool_empty() has an upward reference to the global
> zswap_pools, to sanity check it's not the currently active pool that's
> being freed. That gets the forward decl for zswap_pool_cuyrrent().

nit: zswap_pool_cuyrrent() -> zswap_pool_current() :-)

Also, would it make sense to move zswap_pool_current() above
__zswap_pool_empty() to get rid of the forward declaration? I guess
it's now grouped with current_get() etc. - those don't seem to use the
empty check, so maybe they can also go above __zswap_pool_empty()?


>
> This puts the get and put function above all callers, so kill the
> forward decls as well.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  mm/zswap.c | 94 +++++++++++++++++++++++++++---------------------------
>  1 file changed, 47 insertions(+), 47 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 805d9a35f633..33775f2224b7 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -278,8 +278,6 @@ static inline struct zswap_tree *swap_zswap_tree(swp_entry_t swp)
>
>  static int zswap_writeback_entry(struct zswap_entry *entry,
>                                  swp_entry_t swpentry);
> -static int zswap_pool_get(struct zswap_pool *pool);
> -static void zswap_pool_put(struct zswap_pool *pool);
>
>  static bool zswap_is_full(void)
>  {
> @@ -472,6 +470,53 @@ static void zswap_pool_destroy(struct zswap_pool *pool)
>         kfree(pool);
>  }
>
> +static void __zswap_pool_release(struct work_struct *work)
> +{
> +       struct zswap_pool *pool = container_of(work, typeof(*pool),
> +                                               release_work);
> +
> +       synchronize_rcu();
> +
> +       /* nobody should have been able to get a kref... */
> +       WARN_ON(kref_get_unless_zero(&pool->kref));
> +
> +       /* pool is now off zswap_pools list and has no references. */
> +       zswap_pool_destroy(pool);
> +}
> +
> +static struct zswap_pool *zswap_pool_current(void);
> +
> +static void __zswap_pool_empty(struct kref *kref)
> +{
> +       struct zswap_pool *pool;
> +
> +       pool = container_of(kref, typeof(*pool), kref);
> +
> +       spin_lock(&zswap_pools_lock);
> +
> +       WARN_ON(pool == zswap_pool_current());
> +
> +       list_del_rcu(&pool->list);
> +
> +       INIT_WORK(&pool->release_work, __zswap_pool_release);
> +       schedule_work(&pool->release_work);
> +
> +       spin_unlock(&zswap_pools_lock);
> +}
> +
> +static int __must_check zswap_pool_get(struct zswap_pool *pool)
> +{
> +       if (!pool)
> +               return 0;
> +
> +       return kref_get_unless_zero(&pool->kref);
> +}
> +
> +static void zswap_pool_put(struct zswap_pool *pool)
> +{
> +       kref_put(&pool->kref, __zswap_pool_empty);
> +}
> +
>  /* should be called under RCU */
>  #ifdef CONFIG_MEMCG
>  static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
> @@ -1122,51 +1167,6 @@ static void shrink_worker(struct work_struct *w)
>         zswap_pool_put(pool);
>  }
>
> -static int __must_check zswap_pool_get(struct zswap_pool *pool)
> -{
> -       if (!pool)
> -               return 0;
> -
> -       return kref_get_unless_zero(&pool->kref);
> -}
> -
> -static void __zswap_pool_release(struct work_struct *work)
> -{
> -       struct zswap_pool *pool = container_of(work, typeof(*pool),
> -                                               release_work);
> -
> -       synchronize_rcu();
> -
> -       /* nobody should have been able to get a kref... */
> -       WARN_ON(kref_get_unless_zero(&pool->kref));
> -
> -       /* pool is now off zswap_pools list and has no references. */
> -       zswap_pool_destroy(pool);
> -}
> -
> -static void __zswap_pool_empty(struct kref *kref)
> -{
> -       struct zswap_pool *pool;
> -
> -       pool = container_of(kref, typeof(*pool), kref);
> -
> -       spin_lock(&zswap_pools_lock);
> -
> -       WARN_ON(pool == zswap_pool_current());
> -
> -       list_del_rcu(&pool->list);
> -
> -       INIT_WORK(&pool->release_work, __zswap_pool_release);
> -       schedule_work(&pool->release_work);
> -
> -       spin_unlock(&zswap_pools_lock);
> -}
> -
> -static void zswap_pool_put(struct zswap_pool *pool)
> -{
> -       kref_put(&pool->kref, __zswap_pool_empty);
> -}
> -
>  /*********************************
>  * param callbacks
>  **********************************/
> --
> 2.43.0
>