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References: <20240306184244.754263547@goodmis.org> <550b6c44aa434b5b91e999a8d073527c@AcuMS.aculab.com>
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From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Sun, 10 Mar 2024 20:12:01 +0100
Message-ID: <CAMuHMdUWqZ99vqqgm_qWtuLN0ndmk4oxEEAvBP+mNbCz5ckq6g@mail.gmail.com>
Subject: Re: [for-linus][PATCH 0/3] tracing: Fixes for v6.8
To: David Laight <David.Laight@aculab.com>
Cc: Steven Rostedt <rostedt@goodmis.org>, 
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Masami Hiramatsu <mhiramat@kernel.org>, 
	Mark Rutland <mark.rutland@arm.com>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, 
	Andrew Morton <akpm@linux-foundation.org>
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Hi David,

On Sun, Mar 10, 2024 at 7:16=E2=80=AFPM David Laight <David.Laight@aculab.c=
om> wrote:
> >   Another issue that was brought up is that the trace_seq buffer is
> >   also based on PAGE_SIZE even though it is not tied to the architectur=
e
> >   limit like the ring buffer sub-buffer is. Having it be 64K * 2 is
> >   simply just too big and wasting memory on systems with 64K page sizes=
.
> >   It is now hardcoded to 8K which is what all other architectures with
> >   4K PAGE_SIZE has.
>
> Does Linux use a 2k PAGE_SIZE on any architectures?
> IIRC m68k hardware has a 2k page, but Linux might always pair them.
> A 2k page might (or might not) cause grief.

Linux/m68k supports only 4 or 8 KiB page sizes, depending on the
MMU hardware, cfr. [1].  While the MC68851 MMU also supports page sizes
of 256 and 512 bytes, and 1, 2, 8, 16, and 32 KiB, that is not yet
supported by Linux.

I really doubt Linux will ever support pages smaller than 4 KiB...

[1] https://lore.kernel.org/all/20240306141453.3900574-4-arnd@kernel.org/#Z=
2e.:20240306141453.3900574-4-arnd::40kernel.org:1arch:m68k:Kconfig

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
                                -- Linus Torvalds