Re: [External] Re: [RFC PATCH 0/5] mm: Select victim memcg using BPF_OOM_POLICY

[Chuyi Zhou]

Hi,

在 2023/7/27 19:43, Alan Maguire 写道:
> On 27/07/2023 08:36, Chuyi Zhou wrote:
> > This patchset tries to add a new bpf prog type and use it to select
> > a victim memcg when global OOM is invoked. The mainly motivation is
> > the need to customizable OOM victim selection functionality so that
> > we can protect more important app from OOM killer.
>
> It's a nice use case, but at a high level, the approach pursued here
> is, as I understand it, discouraged for new BPF program development.
> Specifically, adding a new BPF program type with semantics like this
> is not preferred. Instead, can you look at using something like
>
> - using "fmod_ret" instead of a new program type
> - use BPF kfuncs instead of helpers.
> - add selftests in tools/testing/selftests/bpf not samples.
>
> There's some examples of how solutions have evolved from the traditional
> approach (adding a new program type, helpers etc) to using kfuncs etc on
> this list - for example HID-BPF and the BPF scheduler series - which
> should help orient you. There are presentations from Linux Plumbers 2022
> that walk through some of this too.
>
> Judging by the sample program example, all you should need here is a way
> to override the return value of bpf_oom_set_policy() - a noinline
> function that by default returns a no-op. It can then be overridden by
> an "fmod_ret" BPF program.
Indeed, I'll try to use kfuncs & fmod_ret.

Thanks for your advice.
--
Chuyi Zhou
> One thing you lose is cgroup specificity at BPF attach time, but you can
> always add predicates based on the cgroup to your BPF program if needed.
>
> Alan
>
> > Chuyi Zhou (5):
> >    bpf: Introduce BPF_PROG_TYPE_OOM_POLICY
> >    mm: Select victim memcg using bpf prog
> >    libbpf, bpftool: Support BPF_PROG_TYPE_OOM_POLICY
> >    bpf: Add a new bpf helper to get cgroup ino
> >    bpf: Sample BPF program to set oom policy
> >
> >   include/linux/bpf_oom.h        |  22 ++++
> >   include/linux/bpf_types.h      |   2 +
> >   include/linux/memcontrol.h     |   6 ++
> >   include/uapi/linux/bpf.h       |  21 ++++
> >   kernel/bpf/core.c              |   1 +
> >   kernel/bpf/helpers.c           |  17 +++
> >   kernel/bpf/syscall.c           |  10 ++
> >   mm/memcontrol.c                |  50 +++++++++
> >   mm/oom_kill.c                  | 185 +++++++++++++++++++++++++++++++++
> >   samples/bpf/Makefile           |   3 +
> >   samples/bpf/oom_kern.c         |  42 ++++++++
> >   samples/bpf/oom_user.c         | 128 +++++++++++++++++++++++
> >   tools/bpf/bpftool/common.c     |   1 +
> >   tools/include/uapi/linux/bpf.h |  21 ++++
> >   tools/lib/bpf/libbpf.c         |   3 +
> >   tools/lib/bpf/libbpf_probes.c  |   2 +
> >   16 files changed, 514 insertions(+)
> >   create mode 100644 include/linux/bpf_oom.h
> >   create mode 100644 samples/bpf/oom_kern.c
> >   create mode 100644 samples/bpf/oom_user.c