netdev - Re: [PATCH net-next v2] net-memcg: Fix scope of sockmem pressure indicators

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Message-ID: <CALvZod5C3yWdgWr83EAdVUCH5PEK8ew7Q+FOt_zGOFOE9HVyQQ@mail.gmail.com>
Date: Mon, 14 Aug 2023 13:18:23 -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>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	Andrew Morton <akpm@...ux-foundation.org>, David Ahern <dsahern@...nel.org>, 
	Yosry Ahmed <yosryahmed@...gle.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, Yu Zhao <yuzhao@...gle.com>, 
	Kefeng Wang <wangkefeng.wang@...wei.com>, Yafang Shao <laoar.shao@...il.com>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, 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>, 
	Vladimir Davydov <vdavydov.dev@...il.com>, Michal Hocko <mhocko@...e.com>, 
	open list <linux-kernel@...r.kernel.org>, 
	"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>, 
	"open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" <cgroups@...r.kernel.org>, 
	"open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" <linux-mm@...ck.org>
Subject: Re: [PATCH net-next v2] net-memcg: Fix scope of sockmem pressure indicators

On Mon, Aug 14, 2023 at 12:09 AM Abel Wu <wuyun.abel@...edance.com> wrote:
>
> Now there are two indicators of socket memory pressure sit inside
> struct mem_cgroup, socket_pressure and tcpmem_pressure, indicating
> memory reclaim pressure in memcg->memory and ->tcpmem respectively.
>
> When in legacy mode (cgroupv1), the socket memory is charged into
> ->tcpmem which is independent of ->memory, so socket_pressure has
> nothing to do with socket's pressure at all. Things could be worse
> by taking socket_pressure into consideration in legacy mode, as a
> pressure in ->memory can lead to premature reclamation/throttling
> in socket.
>
> While for the default mode (cgroupv2), the socket memory is charged
> into ->memory, and ->tcpmem/->tcpmem_pressure are simply not used.
>
> So {socket,tcpmem}_pressure are only used in default/legacy mode
> respectively for indicating socket memory pressure. This patch fixes
> the pieces of code that make mixed use of both.
>
> Fixes: 8e8ae645249b ("mm: memcontrol: hook up vmpressure to socket pressure")
> Signed-off-by: Abel Wu <wuyun.abel@...edance.com>

So, this is undoing the unintended exposure of v2 functionality for
the v1. I wonder if someone might have started depending upon that
behavior but I am more convinced that no one is using v1's tcpmem
accounting due to performance impact. So, this looks good to me.

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

I do think we should start the deprecation process of v1's tcpmem accounting.