linux-kernel - Re: [PATCH v2 1/1] psi: remove 500ms min window size limitation for triggers

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Message-ID: <CAJuCfpHLJGD8U3D_-fpK0njPwLGAZEXuDA9q9DGjd0Q6TxGSjw@mail.gmail.com>
Date:   Tue, 2 May 2023 10:28:32 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tj@...nel.org, hannes@...xchg.org, lizefan.x@...edance.com,
        johunt@...mai.com, mhocko@...e.com, keescook@...omium.org,
        quic_sudaraja@...cinc.com, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] psi: remove 500ms min window size limitation for triggers

On Tue, May 2, 2023 at 10:24 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, May 02, 2023 at 10:20:34AM -0700, Suren Baghdasaryan wrote:
> > On Thu, Mar 2, 2023 at 5:16 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
> > >
> > > On Thu, Mar 2, 2023 at 5:13 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
> > > >
> > > > Current 500ms min window size for psi triggers limits polling interval
> > > > to 50ms to prevent polling threads from using too much cpu bandwidth by
> > > > polling too frequently. However the number of cgroups with triggers is
> > > > unlimited, so this protection can be defeated by creating multiple
> > > > cgroups with psi triggers (triggers in each cgroup are served by a single
> > > > "psimon" kernel thread).
> > > > Instead of limiting min polling period, which also limits the latency of
> > > > psi events, it's better to limit psi trigger creation to authorized users
> > > > only, like we do for system-wide psi triggers (/proc/pressure/* files can
> > > > be written only by processes with CAP_SYS_RESOURCE capability). This also
> > > > makes access rules for cgroup psi files consistent with system-wide ones.
> > > > Add a CAP_SYS_RESOURCE capability check for cgroup psi file writers and
> > > > remove the psi window min size limitation.
> > > >
> > > > Suggested-by: Sudarshan Rajagopalan <quic_sudaraja@...cinc.com>
> > > > Link: https://lore.kernel.org/all/cover.1676067791.git.quic_sudaraja@quicinc.com/
> > > > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > > > Acked-by: Michal Hocko <mhocko@...e.com>
> > > > Acked-by: Johannes Weiner <hannes@...xchg.org>
> > >
> > > Forgot to change the --to field from Tejun to PeterZ.
> > > Peter, just to clarify, this change is targeted for inclusion in your tree.
> >
> > I think this patch slipped through the cracks. Peter, could you please
> > take it into your tree?
>
> Sorry, yes, got lost. I'll go queue it for post -rc1. No urgency with
> this right?

Yes, I'll be merging it into Android branches counting on it making
upstream later on :) Greg will hate me for that but I'll survive.
Thanks!