netdev - 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>