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 pair of new kfuncs, bpf_proactive_reclaim() and bpf_proactive_reclaim_swappiness(), which give BPF direct access to the proactive 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 kfuncs here are for asynchronous, out-of-band reclaim decided independently by a BPF program -- so they are reviewed as separate series. This series carries only the async reclaim piece. Compared to v1, the kfunc interface has been reworked based on review feedback: instead of a thin wrapper around try_to_free_mem_cgroup_pages() exposing raw gfp/reclaim-option knobs, the series now provides use-case-driven kfuncs that perform one proactive reclaim pass with the same parameters memory.reclaim uses. The bpf_thread_wq patches from v1 (old patches 2-3) are dropped from this series: following the discussion in [2], the cgroup-aware workqueue is being superseded by a disaggregated set of async primitives (bpf_kthread/bpf_waitq) that will be developed separately (discussion in [3]), and the selftest now queues its reclaim work through bpf_wq. Patch 1 adds bpf_proactive_reclaim() and bpf_proactive_reclaim_swappiness(), sleepable kfuncs that perform one reclaim pass on a target memcg, like a write to memory.reclaim: swap is allowed, and the anon/file balance follows the cgroup's swappiness or an explicit override in [MIN_SWAPPINESS, MAX_SWAPPINESS] plus SWAPPINESS_ANON_ONLY. Both delegate to try_to_free_mem_cgroup_pages() with GFP_KERNEL and MEMCG_RECLAIM_MAY_SWAP | MEMCG_RECLAIM_PROACTIVE, the same parameters user_proactive_reclaim() uses, and unlike memory.reclaim they do not retry until the requested size is reached. Both refuse to run when the caller already holds PF_MEMALLOC, since a nested try_to_free_mem_cgroup_pages() would clobber the outer reclaim's current->reclaim_state (e.g. MGLRU dereferences current->reclaim_state->mm_walk). Patch 2 (selftests/bpf: add memcg async reclaim test) ties the kfuncs into 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_proactive_reclaim(), with the reclaim work queued asynchronously through bpf_wq. The test asserts that the monitored cgroup's workload finishes faster once async reclaim kicks in. 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 reclaim from, in one self-contained mechanism. Note that, without bpf_thread_wq, the CPU cost of the reclaim work is not yet attributed to a chosen cgroup; that part waits for the async primitives work mentioned above. Changelog: v2: According to the comments of Shakeel Butt, replace bpf_try_to_free_mem_cgroup_pages() with bpf_proactive_reclaim(memcg, size) and bpf_proactive_reclaim_swappiness(memcg, size, swappiness). According to the comments of Kumar Kartikeya Dwivedi, drop patch 2 and patch 3. Remove bpf_thread_wq code in patch 4. According to the comments of sashiko-bot, fix the issues of selftests. [1] https://sashiko.dev/#/message/cover.1779760876.git.zhuhui%40kylinos.cn [2] https://sashiko.dev/#/message/1b58d56976202f26818d31dbd0da2ecb2e2460f5%40linux.dev [3] https://sashiko.dev/#/message/DKNHV09PBQZP.IRQL20BY574I%40gmail.com Hui Zhu (2): mm/bpf: Add bpf_proactive_reclaim kfuncs selftests/bpf: add memcg async reclaim test mm/bpf_memcontrol.c | 95 +++++ .../bpf/prog_tests/memcg_async_reclaim.c | 382 ++++++++++++++++++ .../selftests/bpf/progs/memcg_async_reclaim.c | 167 ++++++++ 3 files changed, 644 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/memcg_async_reclaim.c create mode 100644 tools/testing/selftests/bpf/progs/memcg_async_reclaim.c -- 2.53.0
