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From:   Shakeel Butt <shakeelb@google.com>
Date:   Mon, 18 Sep 2023 08:49:36 -0700
Message-ID: <CALvZod4P3_726Jo_FAoDVTNrYcy1vgp67SSxix1=k8FEKoVM7g@mail.gmail.com>
Subject: Re: [RFC PATCH net-next 3/3] sock: Throttle pressure-aware sockets
 under pressure
To:     Abel Wu <wuyun.abel@bytedance.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Yosry Ahmed <yosryahmed@google.com>,
        Yu Zhao <yuzhao@google.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Yafang Shao <laoar.shao@gmail.com>,
        Kuniyuki Iwashima <kuniyu@amazon.com>,
        Martin KaFai Lau <martin.lau@kernel.org>,
        Breno Leitao <leitao@debian.org>,
        Alexander Mikhalitsyn <alexander@mihalicyn.com>,
        David Howells <dhowells@redhat.com>,
        Jason Xing <kernelxing@tencent.com>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>
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On Mon, Sep 18, 2023 at 12:48=E2=80=AFAM Abel Wu <wuyun.abel@bytedance.com>=
 wrote:
>
> On 9/1/23 2:21 PM, Abel Wu wrote:
> > @@ -3087,8 +3100,20 @@ int __sk_mem_raise_allocated(struct sock *sk, in=
t size, int amt, int kind)
> >       if (sk_has_memory_pressure(sk)) {
> >               u64 alloc;
> >
> > -             if (!sk_under_memory_pressure(sk))
> > +             /* Be more conservative if the socket's memcg (or its
> > +              * parents) is under reclaim pressure, try to possibly
> > +              * avoid further memstall.
> > +              */
> > +             if (under_memcg_pressure)
> > +                     goto suppress_allocation;
> > +
> > +             if (!sk_under_global_memory_pressure(sk))
> >                       return 1;
> > +
> > +             /* Trying to be fair among all the sockets of same
> > +              * protocal under global memory pressure, by allowing
> > +              * the ones that under average usage to raise.
> > +              */
> >               alloc =3D sk_sockets_allocated_read_positive(sk);
> >               if (sk_prot_mem_limits(sk, 2) > alloc *
> >                   sk_mem_pages(sk->sk_wmem_queued +
>
> I totally agree with what Shakeel said in last reply and will try ebpf-
> based solution to let userspace inject proper strategies. But IMHO the
> above hunk is irrelevant to the idea of this patchset, and is the right
> thing to do, so maybe worth a separate patch?
>
> This hunk originally passes the allocation when this socket is below
> average usage even under global and/or memcg pressure. It makes sense
> to do so under global pressure, as the 'average' is in the scope of
> global, but it's really weird from a memcg's point of view. Actually
> this pass condition was present before memcg pressure was introduced.
>
> Please correct me if I missed something, thanks!
>

Please send the patch 1 and this hunk as separate patches with
relevant motivation and reasoning.

thanks,
Shakeel