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

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Message-ID: <CAJuCfpGYzG+3aLjobsXcTSoo9Jo9MCYA_QcROPyLRKEeVHkLGA@mail.gmail.com>
Date: Thu, 24 Oct 2024 14:04:12 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: 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 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/.

>
> >