On Mon, Aug 18, 2025 at 10:01 AM Roman Gushchin <roman.gushchin@xxxxxxxxx> 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@xxxxxxxxxxxxx/ > [2]: https://lore.kernel.org/lkml/20171130152824.1591-1-guro@xxxxxx/ > [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@xxxxxxxxx/ > > > 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 >
