Re: [PATCH v4 2/3] mm/swap: use swap_ops to register swap device's methods

[Usama Arif <usama.arif@linux.dev>]

On 23/04/2026 03:37, Baoquan He wrote:
> On 04/22/26 at 05:33pm, Chris Li wrote:
>> On Tue, Apr 21, 2026 at 6:48 PM Baoquan He <baoquan.he@linux.dev> wrote:
>>>
>>> On 04/17/26 at 07:30pm, Chris Li wrote:
>>>> On Thu, Apr 16, 2026 at 8:40 PM Baoquan He <baoquan.he@linux.dev> wrote:
>>> ...snip...
>>>>> +int init_swap_ops(struct swap_info_struct *sis)
>>>>> +{
>>>>> +       /*
>>>>> +        * ->flags can be updated non-atomically, but that will
>>>>> +        * never affect SWP_FS_OPS, so the data_race is safe.
>>>>> +        */
>>>>> +       if (data_race(sis->flags & SWP_FS_OPS))
>>>>> +               sis->ops = &bdev_fs_swap_ops;
>>>>> +       /*
>>>>> +        * ->flags can be updated non-atomically, but that will
>>>>> +        * never affect SWP_SYNCHRONOUS_IO, so the data_race is safe.
>>>>> +        */
>>>>> +       else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO))
>>>>> +               sis->ops = &bdev_sync_swap_ops;
>>>>> +       else
>>>>> +               sis->ops = &bdev_async_swap_ops;
>>>>> +
>>>>> +       if (!sis->ops || !sis->ops->read_folio || !sis->ops->write_folio)
>>>>> +               return -1;
>>>> Nitpick:
>>>>
>>>> For int type error return, you should use  -EINVAL or some thing with
>>>> error code. If you don't care about error code, change the return type
>>>> to bool instead.
>>>
>>> Thanks for careful reviewing, returning -EINVAL looks better, I will
>>> change like that and repost.
>>
>> You don't have to repost it as a new series. You can post one small
>> incremental update for the -EINVAL change and ask Andrew to fold it
>> in.
>>
>> Hi Andrew,
>>
>> I think this swap ops series can be merge to mm-unstable with the
>> review. Keep in mind that Baoquan might have a very minor follow up
>> patch relate to -EINAL error code.
> 
> The incremental update is as below. I have built and test it.
> 
> diff --git a/mm/swap_io.c b/mm/swap_io.c
> index 77aa8373c087..e2710d5fb44e 100644
> --- a/mm/swap_io.c
> +++ b/mm/swap_io.c
> @@ -625,7 +625,7 @@ int init_swap_ops(struct swap_info_struct *sis)
>  		sis->ops = &bdev_async_swap_ops;
>  
>  	if (!sis->ops || !sis->ops->read_folio || !sis->ops->write_folio)
> -		return -1;
> +		return -EINVAL;
>  
>  	return 0;
>  }
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index af81fa212f1e..7644049a0919 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3518,10 +3518,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  		goto bad_swap_unlock_inode;
>  	}
>  
> -	if (init_swap_ops(si)) {
> -		error = -EINVAL;
> +	if (error = init_swap_ops(si))
>  		goto bad_swap_unlock_inode;
> -	}
>  
>  	si->max = maxpages;
>  	si->pages = maxpages - 1;


Acked-by: Usama Arif <usama.arif@linux.dev>