Re: [PATCH 2/3] mm/swap: use swap_ops to register swap device's methods

[YoungJun Park <youngjun.park@lge.com>]

On Mon, Mar 02, 2026 at 06:40:15PM +0800, Baoquan He wrote:
> This simplifies codes and makes logic clearer. And also makes later any
> new swap device type being added easier to handle.
> 
> Currently there are three types of swap devices: bdev_fs, bdev_sync
> and bdev_async, and only operations read_folio and write_folio are
> included. In the future, there could be more swap device types added
> and more appropriate opeations adapted into swap_ops.
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  include/linux/swap.h |  13 ++++++
>  mm/swap.h            |   1 -
>  mm/swap_io.c         | 102 +++++++++++++++++++++++++------------------
>  mm/swapfile.c        |   2 +
>  mm/zswap.c           |   3 +-
>  5 files changed, 76 insertions(+), 45 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 0effe3cc50f5..448e5e66ec5c 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -19,6 +19,7 @@
>  struct notifier_block;
>  
>  struct bio;
> +struct swap_iocb;
>  
>  struct pagevec;
>  
> @@ -222,6 +223,17 @@ enum {
>  #define SWAP_CLUSTER_MAX_SKIPPED (SWAP_CLUSTER_MAX << 10)
>  #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
>  
> +struct swap_ops {
> +	void (*read_folio)(struct swap_info_struct *sis,
> +			   struct folio *folio,
> +			   struct swap_iocb **plug);
> +	void (*write_folio)(struct swap_info_struct *sis,
> +			    struct folio *folio,
> +			    struct swap_iocb **plug);
> +};

I think swap_iocb is only required for fs-swap
(swap_folio_read_fs/swap_folio_write_fs).

If the goal is to support fs-swap through swap_ops, it might be worth
considering a more complete integration, including activate/deactivate
and swap_rw from aops, rather than only adding read/write hooks.

So.. we could keep SWP_FS_OPS as-is for now and just split
sync/async paths, and revisit a cleaner fs-swap integration later.
(I mean removing fs ops, and call swap_read/write_folio_fs on sync/async ops.)

How do you think? 

Thanks
Youngjun Park