Message-ID: <CAJuCfpG1+bnFwpc4bxut_5tFtFc-s7+u2YF-suefoXq2-NijJw@mail.gmail.com>
Date: Mon, 18 Aug 2025 21:08:27 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: linux-mm@...ck.org, bpf@...r.kernel.org, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...e.com>, 
	David Rientjes <rientjes@...gle.com>, Matt Bobrowski <mattbobrowski@...gle.com>, 
	Song Liu <song@...nel.org>, Kumar Kartikeya Dwivedi <memxor@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 00/14] mm: BPF OOM

On Mon, Aug 18, 2025 at 10:01 AM Roman Gushchin
<roman.gushchin@...ux.dev> wrote:
>
> This patchset adds an ability to customize the out of memory
> handling using bpf.
>
> It focuses on two parts:
> 1) OOM handling policy,
> 2) PSI-based OOM invocation.
>
> The idea to use bpf for customizing the OOM handling is not new, but
> unlike the previous proposal [1], which augmented the existing task
> ranking policy, this one tries to be as generic as possible and
> leverage the full power of the modern bpf.
>
> It provides a generic interface which is called before the existing OOM
> killer code and allows implementing any policy, e.g. picking a victim
> task or memory cgroup or potentially even releasing memory in other
> ways, e.g. deleting tmpfs files (the last one might require some
> additional but relatively simple changes).
>
> The past attempt to implement memory-cgroup aware policy [2] showed
> that there are multiple opinions on what the best policy is.  As it's
> highly workload-dependent and specific to a concrete way of organizing
> workloads, the structure of the cgroup tree etc, a customizable
> bpf-based implementation is preferable over a in-kernel implementation
> with a dozen on sysctls.

s/on/of ?


>
> The second part is related to the fundamental question on when to
> declare the OOM event. It's a trade-off between the risk of
> unnecessary OOM kills and associated work losses and the risk of
> infinite trashing and effective soft lockups.  In the last few years
> several PSI-based userspace solutions were developed (e.g. OOMd [3] or
> systemd-OOMd [4]). The common idea was to use userspace daemons to
> implement custom OOM logic as well as rely on PSI monitoring to avoid
> stalls. In this scenario the userspace daemon was supposed to handle
> the majority of OOMs, while the in-kernel OOM killer worked as the
> last resort measure to guarantee that the system would never deadlock
> on the memory. But this approach creates additional infrastructure
> churn: userspace OOM daemon is a separate entity which needs to be
> deployed, updated, monitored. A completely different pipeline needs to
> be built to monitor both types of OOM events and collect associated
> logs. A userspace daemon is more restricted in terms on what data is
> available to it. Implementing a daemon which can work reliably under a
> heavy memory pressure in the system is also tricky.
>
> [1]: https://lwn.net/ml/linux-kernel/20230810081319.65668-1-zhouchuyi@bytedance.com/
> [2]: https://lore.kernel.org/lkml/20171130152824.1591-1-guro@fb.com/
> [3]: https://github.com/facebookincubator/oomd
> [4]: https://www.freedesktop.org/software/systemd/man/latest/systemd-oomd.service.html
>
> ----
>
> v1:
>   1) Both OOM and PSI parts are now implemented using bpf struct ops,
>      providing a path the future extensions (suggested by Kumar Kartikeya Dwivedi,
>      Song Liu and Matt Bobrowski)
>   2) It's possible to create PSI triggers from BPF, no need for an additional
>      userspace agent. (suggested by Suren Baghdasaryan)
>      Also there is now a callback for the cgroup release event.
>   3) Added an ability to block on oom_lock instead of bailing out (suggested by Michal Hocko)
>   4) Added bpf_task_is_oom_victim (suggested by Michal Hocko)
>   5) PSI callbacks are scheduled using a separate workqueue (suggested by Suren Baghdasaryan)
>
> RFC:
>   https://lwn.net/ml/all/20250428033617.3797686-1-roman.gushchin@linux.dev/
>
>
> Roman Gushchin (14):
>   mm: introduce bpf struct ops for OOM handling
>   bpf: mark struct oom_control's memcg field as TRUSTED_OR_NULL
>   mm: introduce bpf_oom_kill_process() bpf kfunc
>   mm: introduce bpf kfuncs to deal with memcg pointers
>   mm: introduce bpf_get_root_mem_cgroup() bpf kfunc
>   mm: introduce bpf_out_of_memory() bpf kfunc
>   mm: allow specifying custom oom constraint for bpf triggers
>   mm: introduce bpf_task_is_oom_victim() kfunc
>   bpf: selftests: introduce read_cgroup_file() helper
>   bpf: selftests: bpf OOM handler test
>   sched: psi: refactor psi_trigger_create()
>   sched: psi: implement psi trigger handling using bpf
>   sched: psi: implement bpf_psi_create_trigger() kfunc
>   bpf: selftests: psi struct ops test
>
>  include/linux/bpf_oom.h                       |  49 +++
>  include/linux/bpf_psi.h                       |  71 ++++
>  include/linux/memcontrol.h                    |   2 +
>  include/linux/oom.h                           |  12 +
>  include/linux/psi.h                           |  15 +-
>  include/linux/psi_types.h                     |  72 +++-
>  kernel/bpf/verifier.c                         |   5 +
>  kernel/cgroup/cgroup.c                        |  14 +-
>  kernel/sched/bpf_psi.c                        | 337 ++++++++++++++++++
>  kernel/sched/build_utility.c                  |   4 +
>  kernel/sched/psi.c                            | 130 +++++--
>  mm/Makefile                                   |   4 +
>  mm/bpf_memcontrol.c                           | 166 +++++++++
>  mm/bpf_oom.c                                  | 157 ++++++++
>  mm/oom_kill.c                                 | 182 +++++++++-
>  tools/testing/selftests/bpf/cgroup_helpers.c  |  39 ++
>  tools/testing/selftests/bpf/cgroup_helpers.h  |   2 +
>  .../selftests/bpf/prog_tests/test_oom.c       | 229 ++++++++++++
>  .../selftests/bpf/prog_tests/test_psi.c       | 224 ++++++++++++
>  tools/testing/selftests/bpf/progs/test_oom.c  | 108 ++++++
>  tools/testing/selftests/bpf/progs/test_psi.c  |  76 ++++
>  21 files changed, 1845 insertions(+), 53 deletions(-)
>  create mode 100644 include/linux/bpf_oom.h
>  create mode 100644 include/linux/bpf_psi.h
>  create mode 100644 kernel/sched/bpf_psi.c
>  create mode 100644 mm/bpf_memcontrol.c
>  create mode 100644 mm/bpf_oom.c
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/test_oom.c
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/test_psi.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_oom.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_psi.c
>
> --
> 2.50.1
>

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