linux-kernel - Re: [PATCH v3 tip/perf/core 1/4] mm: introduce mmap_lock_speculation

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Message-ID: <CAJuCfpFJG8MS=LMC2saYYRPGv+xs+UXkrPWD9_Eo1VqY=7v1ow@mail.gmail.com>
Date: Thu, 24 Oct 2024 16:33:01 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Andrii Nakryiko <andrii@...nel.org>, 
	linux-trace-kernel@...r.kernel.org, linux-mm@...ck.org, oleg@...hat.com, 
	rostedt@...dmis.org, mhiramat@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, jolsa@...nel.org, paulmck@...nel.org, 
	willy@...radead.org, akpm@...ux-foundation.org, mjguzik@...il.com, 
	brauner@...nel.org, jannh@...gle.com, mhocko@...nel.org, vbabka@...e.cz, 
	shakeel.butt@...ux.dev, hannes@...xchg.org, Liam.Howlett@...cle.com, 
	lorenzo.stoakes@...cle.com
Subject: Re: [PATCH v3 tip/perf/core 1/4] mm: introduce mmap_lock_speculation_{start|end}

On Thu, Oct 24, 2024 at 4:20 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Oct 24, 2024 at 2:04 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
> >
> > On Thu, Oct 24, 2024 at 9:28 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
> > >
> > > On Thu, Oct 24, 2024 at 2:57 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > > >
> > > > On Wed, Oct 23, 2024 at 03:17:01PM -0700, Suren Baghdasaryan wrote:
> > > >
> > > > > > Or better yet, just use seqcount...
> > > > >
> > > > > Yeah, with these changes it does look a lot like seqcount now...
> > > > > I can take another stab at rewriting this using seqcount_t but one
> > > > > issue that Jann was concerned about is the counter being int vs long.
> > > > > seqcount_t uses unsigned, so I'm not sure how to address that if I
> > > > > were to use seqcount_t. Any suggestions how to address that before I
> > > > > move forward with a rewrite?
> > > >
> > > > So if that issue is real, it is not specific to this case. Specifically
> > > > preemptible seqcount will be similarly affected. So we should probably
> > > > address that in the seqcount implementation.
> > >
> > > Sounds good. Let me try rewriting this patch using seqcount_t and I'll
> > > work with Jann on a separate patch to change seqcount_t.
> > > Thanks for the feedback!
> >
> > I posted the patchset to convert mm_lock_seq into seqcount_t and to
> > add speculative functions at
> > https://lore.kernel.org/all/20241024205231.1944747-1-surenb@google.com/.
>
> Thanks, Suren! Hopefully it can land soon!

Would incorporating them into your patchset speed things up? If so,
feel free to include them into your series.
The only required change in your other patches is the renaming of
mmap_lock_speculation_start() to mmap_lock_speculation_begin().

>
> >
> > >
> > > >