linux-kernel - Re: [PATCH v2 2/2] mm: Remove tlb_flush_reason::NR_TLB_FLUSH

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Message-ID: <c1dce926-98bf-4c9e-a40f-1ba9bcf03ad2@lucifer.local>
Date: Tue, 16 Dec 2025 10:32:07 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Tal Zussman <tz2294@...umbia.edu>, Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        x86@...nel.org, Will Deacon <will@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
        Nick Piggin <npiggin@...il.com>, Peter Zijlstra <peterz@...radead.org>,
        David Hildenbrand <david@...nel.org>, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm: Remove tlb_flush_reason::NR_TLB_FLUSH_REASONS

On Mon, Dec 15, 2025 at 08:35:58AM -0500, Mathieu Desnoyers wrote:
> On 2025-12-15 07:40, Lorenzo Stoakes wrote:
> > On Fri, Dec 12, 2025 at 04:08:08AM -0500, Tal Zussman wrote:
> > > This has been unused since it was added 11 years ago in commit
> > > d17d8f9dedb9 ("x86/mm: Add tracepoints for TLB flushes").
> > >
> > > Acked-by: David Hildenbrand <david@...hat.com>
> > > Reviewed-by: Rik van Riel <riel@...riel.com>
> > > Signed-off-by: Tal Zussman <tz2294@...umbia.edu>
> >
> > Hmm, guess just a way of counting the number of reasons, but if nobody's using
> > it that's silly. So:
>
> If TRACE_DEFINE_ENUM was implemented differently [1,2], then we could use
> NR_TLB_FLUSH_REASONS in a static assert to validate that the number of
> exported enum labels matches the enum tlb_flush_reason.
>
> This would catch this kind of discrepancy at compile-time.

Sure, but for the time being this isn't being used, so dead code -> yoink!

We can obviously come back to this as necessary.

>
> Thanks,
>
> Mathieu
>
> [1] https://github.com/lttng/lttng-modules/blob/master/include/instrumentation/events/sched.h#L132
> [2] https://github.com/lttng/lttng-modules/blob/master/include/lttng/tracepoint-event-impl.h#L176
>
> >
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com

Cheers, Lorenzo