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* [PATCH bpf-next 0/4] bpf: BPF-driven proactive memcg reclaim
@ 2026-08-07  7:01 Hui Zhu
  2026-08-07  7:01 ` [PATCH bpf-next 1/4] mm/bpf: Add bpf_try_to_free_mem_cgroup_pages kfunc Hui Zhu
                   ` (3 more replies)
  0 siblings, 4 replies; 5+ messages in thread
From: Hui Zhu @ 2026-08-07  7:01 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann, John Fastabend,
	Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman,
	Kumar Kartikeya Dwivedi, Song Liu, Yonghong Song, Jiri Olsa,
	Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt,
	Muchun Song, JP Kobryn, Andrew Morton, Shuah Khan, davem,
	Jakub Kicinski, Jesper Dangaard Brouer, Stanislav Fomichev,
	KP Singh, Tao Chen, Mykyta Yatsenko, Leon Hwang, Anton Protopopov,
	Amery Hung, Tobias Klauser, Eyal Birger, Rong Tao, Hao Luo,
	Peter Zijlstra, Miguel Ojeda, Nathan Chancellor, Kees Cook,
	Tejun Heo, Jeff Xu, mkoutny, Jan Hendrik Farr, Christian Brauner,
	Randy Dunlap, Brian Gerst, Masahiro Yamada, Willem de Bruijn,
	Jason Xing, Paul Chaignon, Lance Yang, Jiayuan Chen,
	Emil Tsalapatis, Ihor Solodrai, Barry Song, Geliang Tang,
	linux-kernel, bpf, cgroups, linux-mm, netdev, linux-kselftest
  Cc: Hui Zhu

From: Hui Zhu <zhuhui@kylinos.cn>

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


^ permalink raw reply	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2026-08-07  7:04 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-08-07  7:01 [PATCH bpf-next 0/4] bpf: BPF-driven proactive memcg reclaim Hui Zhu
2026-08-07  7:01 ` [PATCH bpf-next 1/4] mm/bpf: Add bpf_try_to_free_mem_cgroup_pages kfunc Hui Zhu
2026-08-07  7:01 ` [PATCH bpf-next 2/4] bpf: add bpf_thread_wq kthread-backed workqueue with cgroup placement Hui Zhu
2026-08-07  7:04 ` [PATCH bpf-next 3/4] selftests/bpf: add thread_wq cgroup test Hui Zhu
2026-08-07  7:04 ` [PATCH bpf-next 4/4] selftests/bpf: add memcg async reclaim test for bpf_wq/bpf_thread_wq Hui Zhu

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