From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-63.mta0.migadu.com [91.218.175.63]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BC6F43D8902 for ; Fri, 11 Sep 2026 02:21:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.63 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789093270; cv=none; b=DJ061WQD6rMsFn12fAd7rqNcDfatqF2h41QfH28+QN/dNuJhquomnAs6a3nzmurxLqj9Ahrgu4vR5mGiL04S5NVoTYM1kvXoeGsvmsHCGSDtzgqBXSK8/AKNP73Z8ZkF5QlW1HK4TF/p11F3L/5hhOPMlyOAwAoHsmp1OSDs+Lc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789093270; c=relaxed/simple; bh=5/1w47pt+5M6oOZ6KogOUzOV3aVzd9z+Eh9KVmbPDK0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=tkxwjRX2+R6C7DBZKE9CdLsm51uDBHn41qpv/1f8ID4zNq6oWxHrJ/GMI713WQjKvXi783vS6jQ/621JcG65yRu2zmoG94jvo/M1oY0VHfOh5DVnE50zy9V/2agUtxppnFq2GXKgKQ59d3hGV3Wq524NXRJiXnknHKBIoOt9PBk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Vwn2jRiV; arc=none smtp.client-ip=91.218.175.63 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Vwn2jRiV" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=5/1w47pt+5M6oOZ6KogOUzOV3aVzd9z+Eh9KVmbPDK0=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789093264; v=1; x=1789698064; b=Vwn2jRiVlNaVbpcOqQcQidYNNWL/S+iwEdLPSW+pZebShAYYNOaAjx7GhmdxHDXpHOsNU7U1 gog9zhSwADXU9v7zTJkmv77A6zqHIwQ0NYa4igJ60kaC2xSDE5Xd7f4QmmKfMt7SxQfWpOg2hpr WO50PVWtUokaUgASermFONEc= X-Envelope-To: linux-kernel@vger.kernel.org Received: by mta12.migadu.com with ESMTPS id e20d4b384e4f25b3; Fri, 11 Sep 2026 02:21:03 +0000 X-Mizu-Trace-ID: e20d4b384e4f25b3 X-Migadu-Flow: FLOW_OUT From: Hui Zhu To: Roman Gushchin , JP Kobryn , Shakeel Butt , Andrew Morton , Andrii Nakryiko , Eduard Zingerman , Ihor Solodrai , Alexei Starovoitov , Daniel Borkmann , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Shuah Khan , Barry Song , Geliang Tang , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Cc: Hui Zhu Subject: [PATCH bpf-next v10 0/2] bpf: BPF-driven proactive memcg reclaim Date: Fri, 11 Sep 2026 10:20:43 +0800 Message-ID: X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Hui Zhu BPF programs can observe memory pressure on a cgroup (e.g. refault stats via bpf_mem_cgroup_page_state()), but cannot act on it: triggering reclaim on a chosen cgroup requires writing to memory.reclaim, which BPF cannot do. This series adds bpf_proactive_reclaim(), a sleepable kfunc performing one proactive reclaim pass on a target memcg, so when and how hard to reclaim is BPF policy rather than hard-coded thresholds. The kfunc is restricted to BPF_PROG_TYPE_SYSCALL so that reclaim always runs in a clean process context: generic sleepable programs may execute with filesystem locks held or in NOFS/NOIO contexts, where the reclaim path could deadlock in filesystem shrinkers. The bpf_wq and task_work callbacks of a SYSCALL program keep its program type and run in process context, so reclaim work can still be queued asynchronously through them, as the selftest does with bpf_wq. The use case we are looking at is protecting high-priority workloads: a BPF program monitors the state of a high-priority cgroup and, when it degrades (e.g. PSI rises or refaults increase, as in the selftest), asynchronously reclaims memory from low-priority cgroups via bpf_wq and bpf_proactive_reclaim(), giving the pressured cgroup more free pages. Another use case: several vendor-maintained kernels carry private implementations that trigger asynchronous reclaim when a memcg enters a certain state. These exist for historical and partly psychological reasons, but the underlying demand is real. We expect BPF-driven proactive reclaim, combined with the BPF hooks for the memory controller currently under discussion and development, to serve these needs in mainline, reducing kernel fragmentation and improving kernel maintainability. Benchmark numbers from the selftest (TEST_MEMCG_ASYNC_RECLAIM_BENCH=1 runs the workload once without the BPF program and once with it; QEMU VM with 8 GiB RAM and 10 vCPUs, 10 runs): the pressured workload finishes in a median of 2.1s with BPF-driven async reclaim versus 12.0s without, a 51%-90% improvement per run. The harvested workload shares the parent's memory.max with it and finishes in a median of 5.1s versus 9.7s, as it has the limit to itself once the pressured workload finishes early. Raw benchmark output of the 10 runs (one line per run, all passed): memcg_async_reclaim: baseline high=4.081880 low=8.951780, reclaim high=2.000056 low=10.872397, high speedup=51.0% memcg_async_reclaim: baseline high=15.803050 low=14.594268, reclaim high=1.567874 low=4.848877, high speedup=90.1% memcg_async_reclaim: baseline high=5.222607 low=4.076494, reclaim high=2.188346 low=3.922446, high speedup=58.1% memcg_async_reclaim: baseline high=11.556587 low=3.222517, reclaim high=2.325903 low=5.303031, high speedup=79.9% memcg_async_reclaim: baseline high=14.481044 low=10.517298, reclaim high=2.309609 low=7.884620, high speedup=84.1% memcg_async_reclaim: baseline high=9.737340 low=2.876915, reclaim high=1.815853 low=9.379357, high speedup=81.4% memcg_async_reclaim: baseline high=16.290141 low=17.152739, reclaim high=1.649337 low=4.978743, high speedup=89.9% memcg_async_reclaim: baseline high=5.176590 low=4.858071, reclaim high=2.356344 low=5.971522, high speedup=54.5% memcg_async_reclaim: baseline high=12.444925 low=13.305078, reclaim high=1.973012 low=4.261413, high speedup=84.1% memcg_async_reclaim: baseline high=16.213717 low=12.608334, reclaim high=2.207762 low=4.317123, high speedup=86.4% Changelog: v10: According to the comments of JP, drop redundant swap.h include, turn swappiness macros into a BTF-visible enum, and clarify the -1 swappiness semantics in docs and code in code patch. report each reclaim outcome via ringbuf and wait for events with timeout instead of sleep-polling, log workload timings instead of failing on them, drop a debug printf, and add a TEST_MEMCG_ASYNC_RECLAIM_BENCH baseline-comparison mode in the selftests patch. Include the benchmark numbers in the cover letter. v9: According to the comments of JP, copy the motivation from the cover letter to the commit message, restructure the kfunc documentation to separate the direct and asynchronous calling contexts, fold the fs-lock warning into the SYSCALL-only rationale, soften the "bounded unit of work" wording (only the reclaim target is capped), and drop the redundant comment above the reclaim kfunc set registration. v8: According to the comments of Andrew, Kumar and Shakeel, drop the bpf_in_reclaim_context() check because the SYSCALL-only restriction already rules out reentrancy. According to the comments of Kumar, Add the swappiness argument to bpf_proactive_reclaim(). v7: According to the comments of JP, clamp the reclaim target of one bpf_proactive_reclaim() call to MEMCG_CHARGE_BATCH so each call is a bounded unit of work, and document the batching policy in the kfunc. selftest: check the target cgroup for dying state before reclaiming from it, and add the memcg_async_reclaim_dying test covering target removal while reclaim is running. v6: According to the comments of Kumar and Shakeel, Restrict bpf_proactive_reclaim() to BPF_PROG_TYPE_SYSCALL by moving it to a dedicated kfunc set registered for that program type only, and document the clean-process-context requirement in its kerneldoc. v5: According to the comments of Andrii, Kumar and Shakeel, remove bpf_proactive_reclaim_swappiness. v4: According to the comments of bot+bpf-ci and sashiko, also check current->reclaim_state to close the fentry-on-trace-iter recursion window in bpf_in_reclaim_context. Return bytes instead of pages ( nr * PAGE_SIZE ) in bpf_proactive_reclaim_pages and bpf_proactive_reclaim_swappiness. Return (unsigned long)-1 on out-of-range swappiness (was 0). Kdoc of both kfuncs: updated Return descriptions; added FS-lock deadlock warning to bpf_proactive_reclaim. Fix potential child process leak in selftests. Use _exit() instead of exit() in forked children in selftests. Rename reclaimed_pages to reclaimed_bytes in selftests. Fix comments issues in selftests. v3: According to the comments of bot+bpf-ci, add a shared helper bpf_proactive_reclaim_pages() that is called by bpf_proactive_reclaim and bpf_proactive_reclaim_swappiness. According to the comments of sashiko and bot+bpf-ci, fix the issues of selftests. 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. Hui Zhu (2): mm/bpf: Add bpf_proactive_reclaim kfunc selftests/bpf: Add memcg async reclaim test mm/bpf_memcontrol.c | 88 +- mm/internal.h | 10 +- .../bpf/prog_tests/memcg_async_reclaim.c | 779 ++++++++++++++++++ .../selftests/bpf/progs/memcg_async_reclaim.c | 288 +++++++ 4 files changed, 1160 insertions(+), 5 deletions(-) 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 -- 2.43.0