From: Shakeel Butt <shakeel.butt@linux.dev>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Hui Zhu <hui.zhu@linux.dev>,
Roman Gushchin <roman.gushchin@linux.dev>,
JP Kobryn <inwardvessel@gmail.com>,
Andrii Nakryiko <andrii@kernel.org>,
Eduard Zingerman <eddyz87@gmail.com>,
Ihor Solodrai <ihor.solodrai@linux.dev>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
Jiri Olsa <jolsa@kernel.org>,
Emil Tsalapatis <emil@etsalapatis.com>,
Shuah Khan <shuah@kernel.org>, Barry Song <baohua@kernel.org>,
Geliang Tang <geliang@kernel.org>,
linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
Hui Zhu <zhuhui@kylinos.cn>
Subject: Re: [PATCH bpf-next v7 1/2] mm/bpf: Add bpf_proactive_reclaim kfunc
Date: Sat, 5 Sep 2026 09:28:46 -0700 [thread overview]
Message-ID: <apxB5tyglnSbqmEu@linux.dev> (raw)
In-Reply-To: <DL7CEX9EX781.23V26M3600JEI@gmail.com>
On Sat, Sep 05, 2026 at 01:23:39PM +0200, Kumar Kartikeya Dwivedi wrote:
> On Fri Sep 4, 2026 at 8:03 PM CEST, Andrew Morton wrote:
> > On Fri, 4 Sep 2026 18:20:19 +0800 "Hui Zhu" <hui.zhu@linux.dev> wrote:
> >
> >> @@ -159,6 +160,74 @@ __bpf_kfunc void bpf_mem_cgroup_flush_stats(struct mem_cgroup *memcg)
> >> mem_cgroup_flush_stats(memcg);
> >> }
> >>
> >> +/*
> >> + * Reclaim must not recurse: try_to_free_mem_cgroup_pages() overwrites
> >> + * current->reclaim_state, so a nested call would corrupt the outer
> >> + * reclaim state. Reclaim windows are marked with PF_MEMALLOC;
> >> + * reclaim_state is also checked because it is installed slightly
> >> + * before PF_MEMALLOC.
> >> + */
> >> +static bool bpf_in_reclaim_context(void)
> >> +{
> >> + return (current->flags & PF_MEMALLOC) || current->reclaim_state;
> >> +}
> >> +
> >
> > Would life improve if try_to_free_mem_cgroup_pages() didn't do that?
> > If try_to_free_mem_cgroup_pages() (or some variant of it) were to
> > permit nesting?
> >
> > rs = new_thing(current, &sc.reclaim_state);
> > ...
> > set_task_reclaim_state(current, rs);
> >
>
> My understanding is that given the current restrictions on where this kfunc can
> be called, this is mostly a defensive and shouldn't be firing (?). Given that,
> we can probably revisit this when such reentrancy is necessary, even though I
> doubt it would be the case in the future. It will at most be invoked from a wq
> callback or a kthread, so should be fine.
>
If with the current restrictions, this recursion can not happen then let's not
add this check here. We never want recursion/reentrancy here.
next prev parent reply other threads:[~2026-09-05 16:28 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-04 10:20 [PATCH bpf-next v7 0/2] bpf: BPF-driven proactive memcg reclaim Hui Zhu
2026-09-04 10:20 ` [PATCH bpf-next v7 1/2] mm/bpf: Add bpf_proactive_reclaim kfunc Hui Zhu
2026-09-04 11:25 ` bot+bpf-ci
2026-09-04 18:03 ` Andrew Morton
2026-09-05 11:23 ` Kumar Kartikeya Dwivedi
2026-09-05 16:28 ` Shakeel Butt [this message]
2026-09-04 10:20 ` [PATCH bpf-next v7 2/2] selftests/bpf: Add memcg async reclaim test Hui Zhu
2026-09-04 11:25 ` bot+bpf-ci
2026-09-05 11:24 ` [PATCH bpf-next v7 0/2] bpf: BPF-driven proactive memcg reclaim Kumar Kartikeya Dwivedi
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