Re: [PATCH 6/9] mm, swap: use the swap table for the swap cache and switch API

[Barry Song <21cnbao@gmail.com>]

> +
> +/*
> + * Helpers for accessing or modifying the swap table of a cluster,
> + * the swap cluster must be locked.
> + */
> +static inline void __swap_table_set(struct swap_cluster_info *ci,
> +                                   unsigned int off, unsigned long swp_tb)
> +{
> +       VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
> +       atomic_long_set(&ci->table[off], swp_tb);
> +}
> +
> +static inline unsigned long __swap_table_get(struct swap_cluster_info *ci,
> +                                            unsigned int off)
> +{
> +       VM_WARN_ON_ONCE(off >= SWAPFILE_CLUSTER);
> +       return atomic_long_read(&ci->table[off]);
> +}
> +

Why should this use atomic_long instead of just WRITE_ONCE and
READ_ONCE?

Thanks
Barry