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

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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.