linux-kernel - Re: Low TCP throughput due to vmpressure with swap enabled

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Date:   Tue, 22 Nov 2022 11:05:46 -0800
From:   Ivan Babrou <ivan@...udflare.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Linux MM <linux-mm@...ck.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        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 Tue, Nov 22, 2022 at 10:59 AM Yu Zhao <yuzhao@...gle.com> wrote:
>
> On Mon, Nov 21, 2022 at 5:53 PM Ivan Babrou <ivan@...udflare.com> wrote:
> >
> > Hello,
> >
> > We have observed a negative TCP throughput behavior from the following commit:
> >
> > * 8e8ae645249b mm: memcontrol: hook up vmpressure to socket pressure
> >
> > It landed back in 2016 in v4.5, so it's not exactly a new issue.
> >
> > The crux of the issue is that in some cases with swap present the
> > workload can be unfairly throttled in terms of TCP throughput.
> >
> > I am able to reproduce this issue in a VM locally on v6.1-rc6 with 8
> > GiB of RAM with zram enabled.
>
> Hi Ivan,
>
> If it's not too much trouble, could you try again with the following?
>   CONFIG_LRU_GEN=y
>   CONFIG_LRU_GEN_ENABLED=y
>
> I haven't tried it myself. But I'll fix whatever doesn't work for you,
> since your team is on the top of my customer list :)

We don't have it in production, since there we have 5.15 LTS (our
kernel team is testing v6.1).

I do have it enabled in my VM running v6.1-rc6 where I was able to
replicate this, so it doesn't seem to help.