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

hui.zhu
2025-11-21T02:46:48Z

2025年11月21日 03:20, "Michal Hocko" <mhocko@suse.com mailto:mhocko@suse.com?to=%22Michal%20Hocko%22%20%3Cmhocko%40suse.com%3E > 写到:

>
> On Thu 20-11-25 09:29:52, hui.zhu@linux.dev wrote:
> [...]
>
> >
> > I generally agree with an idea to use BPF for various memcg-related
> > policies, but I'm not sure how specific callbacks can be used in
> > practice.
> >
> > Hi Roman,
> >
> > Following are some ideas that can use ebpf memcg:
> >
> > Priority‑Based Reclaim and Limits in Multi‑Tenant Environments:
> > On a single machine with multiple tenants / namespaces / containers,
> > under memory pressure it’s hard to decide “who should be squeezed first”
> > with static policies baked into the kernel.
> > Assign a BPF profile to each tenant’s memcg:
> > Under high global pressure, BPF can decide:
> > Which memcgs’ memory.high should be raised (delaying reclaim),
> > Which memcgs should be scanned and reclaimed more aggressively.
> >
> > Online Profiling / Diagnosing Memory Hotspots:
> > A cgroup’s memory keeps growing, but without patching the kernel it’s
> > difficult to obtain fine‑grained information.
> > Attach BPF to the memcg charge/uncharge path:
> > Record large allocations (greater than N KB) with call stacks and
> > owning file/module, and send them to user space via a BPF ring buffer.
> > Based on sampled data, generate:
> > “Top N memory allocation stacks in this container over the last 10 minutes,”
> > Reports of which objects / call paths are growing fastest.
> > This makes it possible to pinpoint the root cause of host memory
> > anomalies without changing application code, which is very useful
> > in operations/ops scenarios.
> >
> > SLO‑Driven Auto Throttling / Scale‑In/Out Signals:
> > Use eBPF to observe memory usage slope, frequent reclaim,
> > or near‑OOM behavior within a memcg.
> > When it decides “OOM is imminent,” instead of just killing/raising
> > limits, it can emit a signal to a control‑plane component.
> > For example, send an event to a user‑space agent to trigger
> > automatic scaling, QPS adjustment, or throttling.
> >
> > Prevent a cgroup from launching a large‑scale fork+malloc attack:
> > BPF checks per‑uid or per‑cgroup allocation behavior over the
> > last few seconds during memcg charge.
> >
> AFAIU, these are just very high level ideas rather than anything you are
> trying to target with this patch series, right?
>
> All I can see is that you add a reclaim hook but it is not really clear
> to me how feasible it is to actually implement a real memory reclaim
> strategy this way.
>
> In prinicipal I am not really opposed but the memory reclaim process is
> rather involved process and I would really like to see there is
> something real to be done without exporting all the MM code to BPF for
> any practical use. Is there any POC out there?

Hi Michal,

I apologize for not delivering a more substantial POC.

I was hesitant to add extensive eBPF support to memcg
because I wasn't certain it aligned with the community's
vision—and such support would require introducing many
eBPF hooks into memcg.

I will add more eBPF hook to memcg and provide a more
meaningful POC in the next version.

Best,
Hui

> --
> Michal Hocko
> SUSE Labs
>