Re: [Bug 221055] New: Hibernate image write 10x slower since commit 0ff67f990bd4 ("mm, swap: remove swap slot cache")

[Kairui Song <ryncsn@gmail.com>]

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On Wed, Feb 11, 2026 at 2:39 AM Kairui Song <ryncsn@gmail.com> wrote:
>
> On Fri, Feb 06, 2026 at 12:11:51PM +0800, Andrew Morton wrote:
> > On Fri, 06 Feb 2026 19:51:38 +0000 bugzilla-daemon@kernel.org wrote:
> >
> > > https://bugzilla.kernel.org/show_bug.cgi?id=221055
> >
> > > === Summary ===
> > >
> > > Hibernate image write 10x slower since commit 0ff67f990bd4 ("mm,
> > > swap: remove swap slot cache")
> >
> > Thanks for all the work you put into this.
>
> > > === Bisect Result ===
> > >
> > > A full git bisect on the vanilla kernel repository
> > > (git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git)
> > > between v6.14 (good) and v6.15 (bad) with 14 iterations
> > > consistently identified this commit:
> > >
> > >   # first bad commit: [0ff67f990bd45726e0d9e91111d998e7a3595b32]
> > >   #   mm, swap: remove swap slot cache
>
> Both are not too hard to fix. Is that's SSD only issue? And
> should we fix this in every LTS or just mainline? It could
> be a bit trouble some if every LTS needs a fix.

Hi All,

After many attempts, I haven't (fully) reproduced it yet. But I do
have a patch, see attachment.

After this patch:
PM: hibernation: Wrote 1559088 kbytes in 0.55 seconds (2834.70 MB/s) - NVME
PM: hibernation: Wrote 2038748 kbytes in 4.04 seconds (504.64 MB/s) - SATA

After 0ff67f990bd4 (the regression commit):
PM: hibernation: Wrote 2224184 kbytes in 0.90 seconds (2471.31 MB/s) - NVME
PM: hibernation: Wrote 2215472 kbytes in 4.44 seconds (498.98 MB/s) - SATA

Before 0ff67f990bd4:
PM: hibernation: Wrote 2222772 kbytes in 0.84 seconds (2646.15 MB/s) - NVME
PM: hibernation: Wrote 2230700 kbytes in 4.47 seconds (499.03 MB/s) - SATA

It seems a bit faster / slower indeed, or maybe just noise. On my
machines 0ff67f990bd4 is not causing an major issue like the one
described in the bugzilla link. I'll try to see if there are more detailed
issues with the test setup.

And can anyone help verify this fix? I'll also try some other SSD later
maybe that's only reproducible with SSD that have very poor 4K performance.

HDD should not be affected because the allocator has a special
way to do HDD allocation.

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