Re: [RFC PATCH v2 0/4] mm/swap: reserve swap areas for deliberate offload

[Chris Li <chrisl@kernel.org>]

On Fri, Sep 25, 2026 at 6:55 PM Matthias Goergens
<matthias.goergens@gmail.com> wrote:
> The series fixes zram selftest device tracking and error reporting, adds
> the swap policy with DRM eligibility checks, and tests routing, workingset
> activation and retained-entry write refusal. It is based on mm-new at
> 995829088503.

Hi Matthias,

I can't find mm-new 995829088503 anymore.

Your patch does not apply cleanly to the current tip of mm-new
mm-unstable, or mm-stable branches.
Do you have a git repo with your patch applied?

mm-new is whatever Andrew can find on the mailing list, regardless of
whether it has been reviewed. That mm-new branch is very unstable,
even more so than mm-unstable, which should at least have some review
already. Maybe consider using mm-stable or mm-unstable as base next
time.

Chris

>
> Feedback is particularly welcome on:
>
> - Activation-time eligibility versus backend placement or migration:
>   is retained-entry refusal, with possible reclaim churn or OOM,
>   acceptable without migration?
> - Eligible-capacity accounting, including overcommit limits and OOM
>   scoring; cache recovery, cluster invalidation and workingset activation.
> - Persistent activation and visibility: current swap listings do not
>   expose the policy.
>
> Validation includes x86 builds, affected arm64 MTE objects and builds
> without swap or memory cgroups. QEMU tests covered routing, retained-entry
> recovery, data integrity and cleanup, with negative controls for write
> refusal and teardown failure.
>
> I have also been using this policy on my own machine with experimental
> bcachefs swap support, with no problems observed so far. Deliberate stress
> testing is confined to VMs; I do not deliberately stress-test this machine.
>
> Changes since v1, incorporating Sashiko's public review [7]:
>
> - Improve selftest isolation, retained-swap measurement and memlock skips.
> - Track allocated zram devices, wait for udev probes and report cleanup
>   errors without deleting data through a mount that could not be released.
> - Clarify activation, capacity reporting and conventional fallback limits.
>
> [1] https://patchew.org/linux/20260825153238.2695446-1-nphamcs@gmail.com/
> [2] https://patchew.org/linux/20260713025644.170839-1-youngjun.park@lge.com/
> [3] https://openzfs.github.io/openzfs-docs/Project%20and%20Community/FAQ.html#using-a-zvol-for-a-swap-device-on-linux
> [4] https://engineering.fb.com/2022/06/20/data-infrastructure/transparent-memory-offloading-more-memory-at-a-fraction-of-the-cost-and-power/
> [5] https://www.kernel.org/doc/html/latest/admin-guide/mm/damon/reclaim.html
> [6] https://www.kernel.org/doc/html/latest/admin-guide/mm/zswap.html
> [7] https://sashiko.dev/#/patchset/20260914104501.3960616-1-matthias.goergens@gmail.com
> [8] https://github.com/util-linux/util-linux/pull/4633
> [9] https://lore.kernel.org/all/20260914105606.3997649-1-matthias.goergens@gmail.com/
>
> v1: https://lore.kernel.org/all/20260914104501.3960616-1-matthias.goergens@gmail.com/
>
> Matthias Goergens (4):
>   selftests: zram: track owned devices and report cleanup failures
>   mm: restrict offload-only swap to proactive reclaim
>   selftests: zram: cover offload-only swap policy
>   selftests: zram: cover retained offload-only entries
>
>  Documentation/mm/swap.rst                     | 105 ++++
>  drivers/gpu/drm/i915/gem/i915_gem_shrinker.c  |   2 +-
>  .../gpu/drm/i915/gem/selftests/huge_pages.c   |   6 +-
>  drivers/gpu/drm/msm/msm_gem_shrinker.c        |   2 +-
>  drivers/gpu/drm/panthor/panthor_gem.c         |   2 +-
>  drivers/gpu/drm/ttm/ttm_backup.c              |   2 +-
>  drivers/gpu/drm/xe/tests/xe_bo.c              |   2 +-
>  include/linux/swap.h                          |  29 +-
>  include/linux/vm_event_item.h                 |   1 +
>  mm/memcontrol.c                               |  20 +-
>  mm/page_io.c                                  |  24 +-
>  mm/swapfile.c                                 | 123 ++++-
>  mm/vmscan.c                                   |  31 +-
>  mm/vmstat.c                                   |   1 +
>  tools/testing/selftests/zram/.gitignore       |   2 +
>  tools/testing/selftests/zram/Makefile         |   4 +-
>  tools/testing/selftests/zram/README           |  20 +-
>  tools/testing/selftests/zram/config           |  10 +-
>  tools/testing/selftests/zram/settings         |   1 +
>  tools/testing/selftests/zram/swap_offload.c   | 425 +++++++++++++++++
>  .../selftests/zram/workingset_offload.c       | 207 ++++++++
>  tools/testing/selftests/zram/zram.sh          |   9 +
>  tools/testing/selftests/zram/zram01.sh        |   9 +-
>  tools/testing/selftests/zram/zram02.sh        |   9 +-
>  tools/testing/selftests/zram/zram03.sh        | 174 +++++++
>  tools/testing/selftests/zram/zram04.sh        | 164 +++++++
>  tools/testing/selftests/zram/zram05.sh        | 447 ++++++++++++++++++
>  tools/testing/selftests/zram/zram_lib.sh      | 189 ++++++--
>  28 files changed, 1926 insertions(+), 94 deletions(-)
>  create mode 100644 tools/testing/selftests/zram/settings
>  create mode 100644 tools/testing/selftests/zram/swap_offload.c
>  create mode 100644 tools/testing/selftests/zram/workingset_offload.c
>  create mode 100755 tools/testing/selftests/zram/zram03.sh
>  create mode 100755 tools/testing/selftests/zram/zram04.sh
>  create mode 100755 tools/testing/selftests/zram/zram05.sh
>
> --
> 2.55.0
>