On 2025/12/30 17:49, Michal Koutný wrote:
> Hi Hui.
>
> On Tue, Dec 30, 2025 at 11:01:58AM +0800, Hui Zhu <[email protected]> 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
