linux-kernel - Re: [PATCH net] sock: Fix misuse of sk_under_memory

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Message-ID: <CALvZod7WrDF8he9djE6i5DyteR5Bz=w35r1q882QDuYb6dWSRg@mail.gmail.com>
Date:   Wed, 16 Aug 2023 09:23:02 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Abel Wu <wuyun.abel@...edance.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Kuniyuki Iwashima <kuniyu@...zon.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        Breno Leitao <leitao@...ian.org>,
        Alexander Mikhalitsyn <alexander@...alicyn.com>,
        David Howells <dhowells@...hat.com>,
        Jason Xing <kernelxing@...cent.com>,
        Glauber Costa <glommer@...allels.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujtsu.com>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] sock: Fix misuse of sk_under_memory_pressure()

On Wed, Aug 16, 2023 at 2:12 AM Abel Wu <wuyun.abel@...edance.com> wrote:
>
> The status of global socket memory pressure is updated when:
>
>   a) __sk_mem_raise_allocated():
>
>         enter: sk_memory_allocated(sk) >  sysctl_mem[1]
>         leave: sk_memory_allocated(sk) <= sysctl_mem[0]
>
>   b) __sk_mem_reduce_allocated():
>
>         leave: sk_under_memory_pressure(sk) &&
>                 sk_memory_allocated(sk) < sysctl_mem[0]
>
> So the conditions of leaving global pressure are inconstant, which
> may lead to the situation that one pressured net-memcg prevents the
> global pressure from being cleared when there is indeed no global
> pressure, thus the global constrains are still in effect unexpectedly
> on the other sockets.
>
> This patch fixes this by ignoring the net-memcg's pressure when
> deciding whether should leave global memory pressure.
>
> Fixes: e1aab161e013 ("socket: initial cgroup code.")
> Signed-off-by: Abel Wu <wuyun.abel@...edance.com>

Acked-by: Shakeel Butt <shakeelb@...gle.com>