Re: [PATCH v4 2/6] mm: remove the implementation of swap_free() and always use swap_free_nr()

[Ryan Roberts]

On 08/05/2024 23:40, Barry Song wrote:
> From: Barry Song <v-songbaohua@xxxxxxxx>
> 
> To streamline maintenance efforts, we propose removing the implementation
> of swap_free(). Instead, we can simply invoke swap_free_nr() with nr
> set to 1. swap_free_nr() is designed with a bitmap consisting of only
> one long, resulting in overhead that can be ignored for cases where nr
> equals 1.
> 
> A prime candidate for leveraging swap_free_nr() lies within
> kernel/power/swap.c. Implementing this change facilitates the adoption
> of batch processing for hibernation.
> 
> Suggested-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Acked-by: Chris Li <chrisl@xxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: Pavel Machek <pavel@xxxxxx>
> Cc: Len Brown <len.brown@xxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>

Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx>

> ---
>  include/linux/swap.h | 10 +++++-----
>  kernel/power/swap.c  |  5 ++---
>  mm/swapfile.c        | 17 ++++-------------
>  3 files changed, 11 insertions(+), 21 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index d1d35e92d7e9..48131b869a4d 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -482,7 +482,6 @@ extern int add_swap_count_continuation(swp_entry_t, gfp_t);
>  extern void swap_shmem_alloc(swp_entry_t);
>  extern int swap_duplicate(swp_entry_t);
>  extern int swapcache_prepare(swp_entry_t);
> -extern void swap_free(swp_entry_t);
>  extern void swap_free_nr(swp_entry_t entry, int nr_pages);
>  extern void swapcache_free_entries(swp_entry_t *entries, int n);
>  extern void free_swap_and_cache_nr(swp_entry_t entry, int nr);
> @@ -561,10 +560,6 @@ static inline int swapcache_prepare(swp_entry_t swp)
>  	return 0;
>  }
>  
> -static inline void swap_free(swp_entry_t swp)
> -{
> -}
> -
>  static inline void swap_free_nr(swp_entry_t entry, int nr_pages)
>  {
>  }
> @@ -613,6 +608,11 @@ static inline void free_swap_and_cache(swp_entry_t entry)
>  	free_swap_and_cache_nr(entry, 1);
>  }
>  
> +static inline void swap_free(swp_entry_t entry)
> +{
> +	swap_free_nr(entry, 1);
> +}
> +
>  #ifdef CONFIG_MEMCG
>  static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
>  {
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index 5bc04bfe2db1..75bc9e3f9d59 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -200,12 +200,11 @@ void free_all_swap_pages(int swap)
>  
>  	while ((node = swsusp_extents.rb_node)) {
>  		struct swsusp_extent *ext;
> -		unsigned long offset;
>  
>  		ext = rb_entry(node, struct swsusp_extent, node);
>  		rb_erase(node, &swsusp_extents);
> -		for (offset = ext->start; offset <= ext->end; offset++)
> -			swap_free(swp_entry(swap, offset));
> +		swap_free_nr(swp_entry(swap, ext->start),
> +			     ext->end - ext->start + 1);
>  
>  		kfree(ext);
>  	}
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index ec12f2b9d229..99e701620562 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1343,19 +1343,6 @@ static void swap_entry_free(struct swap_info_struct *p, swp_entry_t entry)
>  	swap_range_free(p, offset, 1);
>  }
>  
> -/*
> - * Caller has made sure that the swap device corresponding to entry
> - * is still around or has not been recycled.
> - */
> -void swap_free(swp_entry_t entry)
> -{
> -	struct swap_info_struct *p;
> -
> -	p = _swap_info_get(entry);
> -	if (p)
> -		__swap_entry_free(p, entry);
> -}
> -
>  static void cluster_swap_free_nr(struct swap_info_struct *sis,
>  		unsigned long offset, int nr_pages)
>  {
> @@ -1385,6 +1372,10 @@ static void cluster_swap_free_nr(struct swap_info_struct *sis,
>  	unlock_cluster_or_swap_info(sis, ci);
>  }
>  
> +/*
> + * Caller has made sure that the swap device corresponding to entry
> + * is still around or has not been recycled.
> + */
>  void swap_free_nr(swp_entry_t entry, int nr_pages)
>  {
>  	int nr;