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

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Message-ID: <CAEf4BzbHs+XQK9GZQ59VB27s9Jz6AR7fQmX2XTsyTdz050xkOw@mail.gmail.com>
Date: Thu, 24 Oct 2024 22:12:26 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Suren Baghdasaryan <surenb@...gle.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 4:33 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> 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.

I don't really think so. At this point the uprobe part is done (next
revision has a comment style fix, that's all). So I'll just wait for
your patches to be acked and applied, then I'll just do a trivial
rebase. This will be easier for everyone at this point, IMO, to not
couple them into a single patch set with two authors.

Hopefully Peter will take those patches through tip/perf/core, though,
so I don't have to wait for mm and tip trees to converge.

> The only required change in your other patches is the renaming of
> mmap_lock_speculation_start() to mmap_lock_speculation_begin().

Yep, no problem.

>
> >
> > >
> > > >
> > > > >