Message-ID: <31d3fdfa-799e-426b-bb64-42e06392f0b4@huaweicloud.com>
Date: Tue, 30 Dec 2025 21:24:53 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Michal Koutný <mkoutny@...e.com>,
 Hui Zhu <hui.zhu@...ux.dev>, jiayuan.chen@...ux.dev
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Muchun Song <muchun.song@...ux.dev>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>,
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 Jan Hendrik Farr <kernel@...rr.cc>, Christian Brauner <brauner@...nel.org>,
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 Masahiro Yamada <masahiroy@...nel.org>, davem@...emloft.net,
 Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, cgroups@...r.kernel.org,
 bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
 Hui Zhu <zhuhui@...inos.cn>
Subject: Re: [RFC PATCH v2 0/3] Memory Controller eBPF support



On 2025/12/30 17:49, Michal Koutný wrote:
> Hi Hui.
> 
> On Tue, Dec 30, 2025 at 11:01:58AM +0800, Hui Zhu <hui.zhu@...ux.dev> wrote:
>> This allows administrators to suppress low-priority cgroups' memory
>> usage based on custom policies implemented in BPF programs.
> 
> BTW memory.low was conceived as a work-conserving mechanism for
> prioritization of different workloads. Have you tried that? No need to
> go directly to (high) limits. (<- Main question, below are some
> secondary implementation questions/remarks.)
> 
> ...
>> This series introduces a BPF hook that allows reporting
>> additional "pages over high" for specific cgroups, effectively
>> increasing memory pressure and throttling for lower-priority
>> workloads when higher-priority cgroups need resources.
> 
> Have you considered hooking into calculate_high_delay() instead? (That
> function has undergone some evolution so it'd seem like the candidate
> for BPFication.)
> 

+1

This issue[1] might be resolved by hooking into calculate_high_delay().

[1] https://lore.kernel.org/cgroups/4txrfjc5lqkmydmsesfq3l5drmzdio6pkmtfb64sk3ld6bwkhs@w4dkn76s4dbo/T/#t

> ...
>> 3. Cgroup hierarchy management (inheritance during online/offline)
> 
> I see you're copying the program upon memcg creation.
> Configuration copies aren't such a good way to properly handle
> hierarchical behavior.
> I wonder if this could follow the more generic pattern of how BPF progs
> are evaluated in hierarchies, see BPF_F_ALLOW_OVERRIDE and
> BPF_F_ALLOW_MULTI.
> 
> 
>> Example Results
> ...
>> Results show the low-priority cgroup (/sys/fs/cgroup/low) was
>> significantly throttled:
>> - High-priority cgroup: 21,033,377 bogo ops at 347,825 ops/s
>> - Low-priority cgroup: 11,568 bogo ops at 177 ops/s
>>
>> The stress-ng process in the low-priority cgroup experienced a
>> ~99.9% slowdown in memory operations compared to the
>> high-priority cgroup, demonstrating effective priority
>> enforcement through BPF-controlled memory pressure.
> 
> As a demonstrator, it'd be good to compare this with a baseline without
> any extra progs, e.g. show that high-prio performed better and low-prio
> wasn't throttled for nothing.
> 
> Thanks,
> Michal

-- 
Best regards,
Ridong

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