Re: [RFC PATCH v2 0/3] Memory Controller eBPF support

["Michal Koutný" <mkoutny@suse.com>]

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Hi Hui.

On Tue, Dec 30, 2025 at 11:01:58AM +0800, Hui Zhu <hui.zhu@linux.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.)

...
> 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

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