Re: Low TCP throughput due to vmpressure with swap enabled

Ivan Babrou
2022-11-22T19:06:39Z

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.