Re: [PATCH 1/2] mm/zswap: make sure each swapfile always have zswap rb-tree

[Nhat Pham <nphamcs@gmail.com>]

On Wed, Jan 17, 2024 at 1:23 AM Chengming Zhou
<zhouchengming@bytedance.com> wrote:
>
> Not all zswap interfaces can handle the absence of the zswap rb-tree,
> actually only zswap_store() has handled it for now.
>
> To make things simple, we make sure each swapfile always have the
> zswap rb-tree prepared before being enabled and used. The preparation
> is unlikely to fail in practice, this patch just make it explicit.
>
> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>

This seems fine to me. IIUC, zswap_swapon() only fails when the rbtree
allocation fails, and the tree's memory footprint is small so that's
unlikely anyway.

Acked-by: Nhat Pham <nphamcs@gmail.com>



> ---
>  include/linux/zswap.h |  7 +++++--
>  mm/swapfile.c         | 10 +++++++---
>  mm/zswap.c            |  7 ++++---
>  3 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/zswap.h b/include/linux/zswap.h
> index 0b709f5bc65f..eca388229d9a 100644
> --- a/include/linux/zswap.h
> +++ b/include/linux/zswap.h
> @@ -30,7 +30,7 @@ struct zswap_lruvec_state {
>  bool zswap_store(struct folio *folio);
>  bool zswap_load(struct folio *folio);
>  void zswap_invalidate(int type, pgoff_t offset);
> -void zswap_swapon(int type);
> +int zswap_swapon(int type);
>  void zswap_swapoff(int type);
>  void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg);
>  void zswap_lruvec_state_init(struct lruvec *lruvec);
> @@ -51,7 +51,10 @@ static inline bool zswap_load(struct folio *folio)
>  }
>
>  static inline void zswap_invalidate(int type, pgoff_t offset) {}
> -static inline void zswap_swapon(int type) {}
> +static inline int zswap_swapon(int type)
> +{
> +       return 0;
> +}
>  static inline void zswap_swapoff(int type) {}
>  static inline void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) {}
>  static inline void zswap_lruvec_state_init(struct lruvec *lruvec) {}
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 3eec686484ef..6c53ea06626b 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2347,8 +2347,6 @@ static void enable_swap_info(struct swap_info_struct *p, int prio,
>                                 unsigned char *swap_map,
>                                 struct swap_cluster_info *cluster_info)
>  {
> -       zswap_swapon(p->type);
> -
>         spin_lock(&swap_lock);
>         spin_lock(&p->lock);
>         setup_swap_info(p, prio, swap_map, cluster_info);
> @@ -3166,6 +3164,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>         if (error)
>                 goto bad_swap_unlock_inode;
>
> +       error = zswap_swapon(p->type);
> +       if (error)
> +               goto free_swap_address_space;
> +
>         /*
>          * Flush any pending IO and dirty mappings before we start using this
>          * swap device.
> @@ -3174,7 +3176,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>         error = inode_drain_writes(inode);
>         if (error) {
>                 inode->i_flags &= ~S_SWAPFILE;
> -               goto free_swap_address_space;
> +               goto free_swap_zswap;
>         }
>
>         mutex_lock(&swapon_mutex);
> @@ -3198,6 +3200,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>
>         error = 0;
>         goto out;
> +free_swap_zswap:
> +       zswap_swapoff(p->type);
>  free_swap_address_space:
>         exit_swap_address_space(p->type);
>  bad_swap_unlock_inode:
> diff --git a/mm/zswap.c b/mm/zswap.c
> index ca25b676048e..d88faea85978 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1519,7 +1519,7 @@ bool zswap_store(struct folio *folio)
>         if (folio_test_large(folio))
>                 return false;
>
> -       if (!zswap_enabled || !tree)
> +       if (!zswap_enabled)
>                 return false;
>
>         /*
> @@ -1772,19 +1772,20 @@ void zswap_invalidate(int type, pgoff_t offset)
>         spin_unlock(&tree->lock);
>  }
>
> -void zswap_swapon(int type)
> +int zswap_swapon(int type)
>  {
>         struct zswap_tree *tree;
>
>         tree = kzalloc(sizeof(*tree), GFP_KERNEL);
>         if (!tree) {
>                 pr_err("alloc failed, zswap disabled for swap type %d\n", type);
> -               return;
> +               return -ENOMEM;
>         }
>
>         tree->rbroot = RB_ROOT;
>         spin_lock_init(&tree->lock);
>         zswap_trees[type] = tree;
> +       return 0;
>  }
>
>  void zswap_swapoff(int type)
>
> --
> b4 0.10.1