Re: [RFC PATCH v4 1/3] mm/zswap: release retired pools via queue_rcu_work() instead of synchronize_rcu()

[Yosry Ahmed]

On Sun, Aug 30, 2026 at 4:47 AM Jianyue Wu <wujianyue000@xxxxxxxxx> wrote:
>
> When a pool's last reference is dropped, __zswap_pool_empty() removes it
> from the pool list and schedules __zswap_pool_release(), which calls
> synchronize_rcu() to wait for readers before tearing the pool down.
>
> synchronize_rcu() is a synchronous, potentially long wait.  Replace it
> with queue_rcu_work(): __zswap_pool_empty() hands the pool to
> queue_rcu_work(), which waits for a grace period asynchronously and then
> runs __zswap_pool_release() from a worker for the sleepable teardown
> (__zswap_pool_empty() can run in atomic context and must not block).
> The grace-period guarantee is unchanged; the retirement path just no
> longer blocks on it.
>
> Suggested-by: Yosry Ahmed <yosry@xxxxxxxxxx>
> Signed-off-by: Jianyue Wu <wujianyue000@xxxxxxxxx>

Why are the patches still tagged RFC?

Anyway, with one nit below:

Acked-by: Yosry Ahmed <yosry@xxxxxxxxxx>

> ---
>  mm/zswap.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 37f34e406c8e..0bb30e58950a 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -155,7 +155,7 @@ struct zswap_pool {
>         struct crypto_acomp_ctx __percpu *acomp_ctx;
>         struct percpu_ref ref;
>         struct list_head list;
> -       struct work_struct release_work;
> +       struct rcu_work release_work;

Seems like the convention is to use rwork in the name instead of work.

>         struct hlist_node node;
>         char tfm_name[CRYPTO_MAX_ALG_NAME];
>  };
> @@ -379,10 +379,8 @@ static void zswap_pool_destroy(struct zswap_pool *pool)
>
>  static void __zswap_pool_release(struct work_struct *work)
>  {
> -       struct zswap_pool *pool = container_of(work, typeof(*pool),
> -                                               release_work);
> -
> -       synchronize_rcu();
> +       struct zswap_pool *pool = container_of(to_rcu_work(work),
> +                                              typeof(*pool), release_work);
>
>         /* nobody should have been able to get a ref... */
>         WARN_ON(!percpu_ref_is_zero(&pool->ref));
> @@ -406,8 +404,8 @@ static void __zswap_pool_empty(struct percpu_ref *ref)
>
>         list_del_rcu(&pool->list);
>
> -       INIT_WORK(&pool->release_work, __zswap_pool_release);
> -       schedule_work(&pool->release_work);
> +       INIT_RCU_WORK(&pool->release_work, __zswap_pool_release);
> +       queue_rcu_work(system_percpu_wq, &pool->release_work);
>
>         spin_unlock_bh(&zswap_pools_lock);
>  }
> --
> 2.43.0
>