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Date: Mon, 5 Dec 2022 19:28:14 +0000 From: Shakeel Butt <shakeelb@...gle.com> To: Johannes Weiner <hannes@...xchg.org> Cc: Ivan Babrou <ivan@...udflare.com>, Linux MM <linux-mm@...ck.org>, Linux Kernel Network Developers <netdev@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org>, Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <songmuchun@...edance.com>, Andrew Morton <akpm@...ux-foundation.org>, Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, cgroups@...r.kernel.org, kernel-team <kernel-team@...udflare.com> Subject: Re: Low TCP throughput due to vmpressure with swap enabled On Mon, Nov 28, 2022 at 01:07:25PM -0500, Johannes Weiner wrote: > [...] > > With the patch applied I'm capped at ~120MB/s, which is a symptom of a > > clamped window. > > > > I can't find any sockets with memcg->socket_pressure = 1, but at the > > same time I only see the following rcv_ssthresh assigned to sockets: > > Hm, I don't see how socket accounting would alter the network behavior > other than through socket_pressure=1. > I think what is happening is that the tcp stack is calling tcp_under_memory_pressure() and making decisions without going through the memcg charge codepath which set or reset memcg->socket_pressure. Most probably the socket is clamped due to memcg->socket_pressure and then the kernel never tried to grow its buffers because memcg->socket_pressure is still set and thus never tried the memcg charge codepath which would have reset memcg->socket_pressure. (Maybe) That is my guess but network experts CCed can correct me. Anyways, I don't think the pressure mechanism which relies on successful charging will work. I am brainstorming towards memory.high based network throttling. Basically use penalty_jiffies (or something similar) to set memcg->socket_pressure. However I want this to be opt-in as we do have applications which prefer to be killed than be throttled. So, still working on the fine details how this can be done without introducing a rigid API.
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