Re: [PATCH v4 1/3] mm, swap: speed up hibernation allocation and writeout

[Kairui Song <ryncsn@gmail.com>]

On Tue, Feb 17, 2026 at 5:42 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Mon, 16 Feb 2026 22:58:02 +0800 Kairui Song via B4 Relay <devnull+kasong.tencent.com@kernel.org> wrote:
>
> > From: Kairui Song <kasong@tencent.com>
> >
> > Since commit 0ff67f990bd4 ("mm, swap: remove swap slot cache"),
> > hibernation has been using the swap slot slow allocation path for
> > simplification, which turns out might cause regression for some
> > devices because the allocator now rotates clusters too often, leading to
> > slower allocation and more random distribution of data.
> >
> > Fast allocation is not complex, so implement hibernation support as
> > well.
> >
> > Test result with Samsung SSD 830 Series (SATA II, 3.0 Gbps) shows the
> > performance is several times better [1]:
> > 6.19:               324 seconds
> > After this series:  35 seconds
>
> Thanks.
>
> I'll merge only [1/3] at this time, into mm-unstable at this time (I'll
> move it to mm-unstable after resyncing mm.git with upstream).
>
> We don't want the other two patches present during testing of this
> backportable fix because doing so partially invalidates that testing -
> [2/3] and[3/3] might accidentally fix issues which [1/3] added.  It happens,
> occasionally.

Sounds good to me. I'll send the cleanup separately sometime later again.

>
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -1926,8 +1926,9 @@ void swap_put_entries_direct(swp_entry_t entry, int nr)
> >  /* Allocate a slot for hibernation */
> >  swp_entry_t swap_alloc_hibernation_slot(int type)
> >  {
> > -     struct swap_info_struct *si = swap_type_to_info(type);
> > -     unsigned long offset;
> > +     struct swap_info_struct *pcp_si, *si = swap_type_to_info(type);
> > +     unsigned long pcp_offset, offset = SWAP_ENTRY_INVALID;
> > +     struct swap_cluster_info *ci;
> >       swp_entry_t entry = {0};
> >
> >       if (!si)
> > @@ -1937,11 +1938,21 @@ swp_entry_t swap_alloc_hibernation_slot(int type)
> >       if (get_swap_device_info(si)) {
> >               if (si->flags & SWP_WRITEOK) {
> >                       /*
> > -                      * Grab the local lock to be compliant
> > -                      * with swap table allocation.
> > +                      * Try the local cluster first if it matches the device. If
> > +                      * not, try grab a new cluster and override local cluster.
> >                        */
>
> nanonit, worrying about 80-cols is rather old fashioned but there's no
> reason to overflow 80 in a block comment!

I'll be more careful about this, thanks.