From: Hui Zhu <[email protected]> This series lets a BPF program decide when to trigger memcg reclaim and how aggressively to do it, based on whatever runtime signal it chooses to observe -- rather than reclaim only being triggered once a cgroup's usage crosses a fixed threshold. The core idea is a new kfunc, bpf_try_to_free_mem_cgroup_pages(), which gives BPF direct access to the reclaim path so this decision can be made in BPF policy rather than hard-coded threshold logic.
This was originally part of a larger series posted here [1]. That series also adds a memcg BPF struct_ops (memcg_charged, memcg_uncharged, below_low, below_min) for synchronous, in-line memory protection decisions. That mechanism and this one solve different problems -- struct_ops hooks run inline on the charge/reclaim path, while the kfunc here is for asynchronous, out-of-band reclaim decided independently by a BPF program -- so I think they're better reviewed as separate series rather than bundled together. This series carries only the async reclaim piece: the bpf_try_to_free_mem_cgroup_pages kfunc (patch 1), plus a new bpf_thread_wq mechanism (patch 2) that grew out of discussion here [2]. Patch 1 adds bpf_try_to_free_mem_cgroup_pages(), a sleepable kfunc wrapping try_to_free_mem_cgroup_pages(). With it, a BPF program can reclaim from a given cgroup on its own terms -- any condition it can observe at runtime -- instead of being limited to "usage hit threshold X". Patch 2 adds bpf_thread_wq, a bpf_wq-like map field backed by a dedicated kthread_worker rather than the system workqueue, which can be attached to a specific cgroup at init time. The motivation is accounting: reclaim work triggered from BPF still costs CPU (and can itself touch memory), and running it via a plain irq_work/system workqueue callback would charge that cost to whatever context happens to run it, not to the cgroup the policy cares about. bpf_thread_wq lets that cost be attributed to a chosen cgroup instead -- e.g. the low-priority cgroup being reclaimed from. Patch 3 is a selftest that exercises bpf_thread_wq's cgroup attachment in isolation: verifying the callback observes the target cgroup when one is given, and does not when it isn't. Patch 4 (selftests/bpf: add memcg async reclaim test for bpf_wq/bpf_thread_wq) ties patches 1 and 2 together as a worked example: it watches the WORKINGSET_REFAULT_FILE counter of a high-priority cgroup as a proxy for memory-pressure impact, and once it starts climbing, proactively reclaims pages from a low-priority cgroup via bpf_try_to_free_mem_cgroup_pages, running that reclaim inside a bpf_thread_wq attached to the low-priority cgroup so the reclaim cost lands on it rather than leaking into an unrelated context. This demonstrates the end-to-end use case: BPF observes pressure on the cgroup it wants to protect, and reclaims from the cgroup it wants to charge, in one self-contained mechanism. [1] https://sashiko.dev/#/message/cover.1779760876.git.zhuhui%40kylinos.cn [2] https://sashiko.dev/#/message/1b58d56976202f26818d31dbd0da2ecb2e2460f5%40linux.dev Hui Zhu (4): mm/bpf: Add bpf_try_to_free_mem_cgroup_pages kfunc bpf: add bpf_thread_wq kthread-backed workqueue with cgroup placement selftests/bpf: add thread_wq cgroup test selftests/bpf: add memcg async reclaim test for bpf_wq/bpf_thread_wq include/linux/bpf.h | 15 +- include/linux/cgroup.h | 2 + include/uapi/linux/bpf.h | 4 + kernel/bpf/btf.c | 7 + kernel/bpf/helpers.c | 418 +++++++++++++++ kernel/bpf/syscall.c | 15 +- kernel/bpf/verifier.c | 44 +- kernel/cgroup/cgroup.c | 13 + mm/bpf_memcontrol.c | 58 +++ .../testing/selftests/bpf/bpf_experimental.h | 7 + .../bpf/prog_tests/memcg_async_reclaim.c | 479 ++++++++++++++++++ .../bpf/prog_tests/thread_wq_cgroup.c | 87 ++++ .../selftests/bpf/progs/memcg_async_reclaim.c | 255 ++++++++++ .../selftests/bpf/progs/thread_wq_cgroup.c | 56 ++ 14 files changed, 1455 insertions(+), 5 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/memcg_async_reclaim.c create mode 100644 tools/testing/selftests/bpf/prog_tests/thread_wq_cgroup.c create mode 100644 tools/testing/selftests/bpf/progs/memcg_async_reclaim.c create mode 100644 tools/testing/selftests/bpf/progs/thread_wq_cgroup.c -- 2.53.0
