Re: Low TCP throughput due to vmpressure with swap enabled

Yu Zhao
2022-11-22T19:08:55Z

On Tue, Nov 22, 2022 at 12:05 PM Ivan Babrou <ivan@cloudflare.com> wrote:
>
> On Tue, Nov 22, 2022 at 10:59 AM Yu Zhao <yuzhao@google.com> wrote:
> >
> > On Mon, Nov 21, 2022 at 5:53 PM Ivan Babrou <ivan@cloudflare.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.

Thanks. I'll look into this and get back to you.