Re: [PATCH v3 1/6] mm: swap: introduce swap_free_nr() for batched swap_free()

[Ryan Roberts <ryan.roberts@arm.com>]

On 03/05/2024 01:50, Barry Song wrote:
> From: Chuanhua Han <hanchuanhua@oppo.com>
> 
> While swapping in a large folio, we need to free swaps related to the whole
> folio. To avoid frequently acquiring and releasing swap locks, it is better
> to introduce an API for batched free.
> Furthermore, this new function, swap_free_nr(), is designed to efficiently
> handle various scenarios for releasing a specified number, nr, of swap
> entries.
> 
> Signed-off-by: Chuanhua Han <hanchuanhua@oppo.com>
> Co-developed-by: Barry Song <v-songbaohua@oppo.com>
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>

This looks much better!

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


> ---
>  include/linux/swap.h |  5 +++++
>  mm/swapfile.c        | 47 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 11c53692f65f..d1d35e92d7e9 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -483,6 +483,7 @@ 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);
>  int swap_type_of(dev_t device, sector_t offset);
> @@ -564,6 +565,10 @@ static inline void swap_free(swp_entry_t swp)
>  {
>  }
>  
> +static inline void swap_free_nr(swp_entry_t entry, int nr_pages)
> +{
> +}
> +
>  static inline void put_swap_folio(struct folio *folio, swp_entry_t swp)
>  {
>  }
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index f6ca215fb92f..ec12f2b9d229 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1356,6 +1356,53 @@ void swap_free(swp_entry_t entry)
>  		__swap_entry_free(p, entry);
>  }
>  
> +static void cluster_swap_free_nr(struct swap_info_struct *sis,
> +		unsigned long offset, int nr_pages)
> +{
> +	struct swap_cluster_info *ci;
> +	DECLARE_BITMAP(to_free, BITS_PER_LONG) = { 0 };
> +	int i, nr;
> +
> +	ci = lock_cluster_or_swap_info(sis, offset);
> +	while (nr_pages) {
> +		nr = min(BITS_PER_LONG, nr_pages);
> +		for (i = 0; i < nr; i++) {
> +			if (!__swap_entry_free_locked(sis, offset + i, 1))
> +				bitmap_set(to_free, i, 1);
> +		}
> +		if (!bitmap_empty(to_free, BITS_PER_LONG)) {
> +			unlock_cluster_or_swap_info(sis, ci);
> +			for_each_set_bit(i, to_free, BITS_PER_LONG)
> +				free_swap_slot(swp_entry(sis->type, offset + i));
> +			if (nr == nr_pages)
> +				return;
> +			bitmap_clear(to_free, 0, BITS_PER_LONG);
> +			ci = lock_cluster_or_swap_info(sis, offset);
> +		}
> +		offset += nr;
> +		nr_pages -= nr;
> +	}
> +	unlock_cluster_or_swap_info(sis, ci);
> +}
> +
> +void swap_free_nr(swp_entry_t entry, int nr_pages)
> +{
> +	int nr;
> +	struct swap_info_struct *sis;
> +	unsigned long offset = swp_offset(entry);
> +
> +	sis = _swap_info_get(entry);
> +	if (!sis)
> +		return;
> +
> +	while (nr_pages) {
> +		nr = min_t(int, nr_pages, SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER);
> +		cluster_swap_free_nr(sis, offset, nr);
> +		offset += nr;
> +		nr_pages -= nr;
> +	}
> +}
> +
>  /*
>   * Called after dropping swapcache to decrease refcnt to swap entries.
>   */