linux-kernel - Re: [for-linus][PATCH 0/3] tracing: Fixes for v6.8

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Date: Sun, 10 Mar 2024 20:12:01 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: David Laight <David.Laight@...lab.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [for-linus][PATCH 0/3] tracing: Fixes for v6.8

Hi David,

On Sun, Mar 10, 2024 at 7:16 PM David Laight <David.Laight@...lab.com> 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 architecture
> >   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/#Z2e.:20240306141453.3900574-4-arnd::40kernel.org:1arch:m68k:Kconfig

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds