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

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

On Mon, 14 Sep 2026 14:31:39 +0800 Baoquan He <baoquan.he@linux.dev> wrote:

> > 
> > >  	si = get_swap_device(swpentry);
> > >  	if (!si)
> > > -		return -EEXIST;
> > > +		return -ENOENT;
> > 
> > mm-new has changed.  I made this
> 
> Thanks. Does it need a v2? or just use ther version you tuned.

I fixed it up while fixing the rejects, I hope.  Below.

> By the way, which mm branch is suggested to take as a base for mm
> patches posting? I usually take mm-unstable branch, seems it's changed
> to mm-new now?

mm-new is a front-end to mm-unstable.  The only difference is that
mm-new isn't included in linux-next.  New material goes into mm-new and
if it hasn't caused any disasters for a few days I'll move it into
mm-unstable and hence linux-next.

Ordinarily there isn't much material in mm-new.  At this moment
mm-unstable has 405 patches and mm-new has another 96.  That 96 is
unusually large because people have been sending huge patchsets today.

So mm-new is the best target for my merging pleasure but it is surely a
pain for ongoing development - it's changing at a great rate.  Those
500 patches landed in 15 days.

I suggest a reasonable process is, approximately, to develop against
mainline (or mm-stable if there's anything in it) until you think the
code is ready for mm.git.  Then rebase/retest against mm-new and send
it out.  But keep an eye on what's happening in mm.git so that the
rebasing doesn't cause nasty surprises.



From: Baoquan He <hebaoquan@kylinos.cn>
Subject: mm: zswap: return -ENOENT when the swap device is gone
Date: Sun, 13 Sep 2026 14:30:31 +0800

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.

Link: https://lore.kernel.org/20260913063031.1689420-1-hebaoquan@kylinos.cn
Signed-off-by: Baoquan He <hebaoquan@kylinos.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
---

 mm/zswap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/zswap.c~mm-zswap-return-enoent-when-the-swap-device-is-gone
+++ a/mm/zswap.c
@@ -1016,7 +1016,7 @@ static int zswap_writeback_entry(struct
 	/* try to allocate swap cache folio */
 	si = get_swap_device(swpentry);
 	if (IS_ERR_OR_NULL(si))
-		return -EEXIST;
+		return -ENOENT;
 
 	mpol = get_task_policy(current);
 	folio = swap_cache_alloc_folio(swpentry, GFP_KERNEL, BIT(0), NULL, mpol,
_