Re: [PATCH] mm: zswap: return -ENOENT when the swap device is gone

[Andrew Morton <akpm@linux-foundation.org>]

On Sun, 13 Sep 2026 14:30:31 +0800 Baoquan He <hebaoquan@kylinos.cn> wrote:

> zswap_writeback_entry() returns -EEXIST when get_swap_device() finds no
> device.  -EEXIST is the shrinker's "page already in swap cache" signal,
> which makes zswap_shrinker_scan() stop shrinking entirely.  A NULL
> get_swap_device() instead means the device is being swapped off, so the
> entry is simply stale.
> 
> Return -ENOENT so the shrinker skips the stale entry and keeps scanning.
> Independent of xswap; affects all swap devices.
> 
> ...
>
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -998,7 +998,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>  	/* try to allocate swap cache folio */

Comment was always lame ("say why, not what").  It now seems flat out wrong?

>  	si = get_swap_device(swpentry);
>  	if (!si)
> -		return -EEXIST;
> +		return -ENOENT;

mm-new has changed.  I made this


	/* try to allocate swap cache folio */
	si = get_swap_device(swpentry);
	if (IS_ERR_OR_NULL(si))
		return -ENOENT;