Re: [PATCH v3] PM: hibernate: call preallocate_image after freeze prepare

[Matthew Leach]

Hi Rafael,

"Rafael J. Wysocki" <rafael@xxxxxxxxxx> writes:

> On Fri, Apr 3, 2026 at 9:36 AM Matthew Leach
> <matthew.leach@xxxxxxxxxxxxx> wrote:
>>

[...]

> Can you please have a look at
>
> https://sashiko.dev/#/patchset/20260403-hibernation-fixes-v3-1-31bc9fa3ba2d%40collabora.com

[pasting comment in-line here for comment]

> Does this relocation introduce a deadlock during memory reclaim?
> 
> hibernate_preallocate_memory() allocates a large amount of memory and
> triggers direct reclaim. Direct reclaim needs to write back dirty file
> pages and swap out anonymous pages.
> 
> Since freeze_kernel_threads() just ran, threads required for I/O
> completion (like kswapd, jbd2 for Ext4, or WQ_FREEZABLE workqueues) are
> currently frozen. Will the I/O for page reclaim block indefinitely
> waiting on these frozen threads?

The existing code already performs a memory reclaim after
freeze_kernel_threads(). The old shrink_shmem_memory() called
shrink_all_memory() in the same position, after both
freeze_kernel_threads() and dpm_prepare(). This isn't a new pattern
being introduced by this patch.

Nevertheless, the call chain looks like:

shrink_all_memory()
  -> do_try_to_free_pages()
    -> shrink_zones()
      -> shrink_node()
        -> shrink_folio_list()
          -> pageout()

pageout() only writes back shmem and anonymous folios to swap; so jdb2
and other FS threads being frozen isn't a concern. For the swap write
out, the I/O submission path is via submit_bio() which is also
synchronous.

> Additionally, because the OOM killer is already disabled by
> freeze_processes() earlier in the hibernation path, can the reclaim path
> get stuck permanently without being able to fall back to killing
> processes?

There's nothing new here regarding the OOM killer. freeze_processes()
disables it in hibernate() prior to calling hibernation_snapshot().
Since this patch is entirely contained within hibernation_snapshot()
that pattern hasn't changed.

Regards,
-- 
Matt