linux-kernel - Re: [PATCH] m68k: Enable dead code elimination

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Message-ID: <CAMuHMdVEO+o0Py3ioC6ohbJooQdMhD9AXTHD1j1y+C_1TqSAAg@mail.gmail.com>
Date: Sun, 6 Jul 2025 12:43:50 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Daniel Palmer <daniel@...f.com>
Cc: linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] m68k: Enable dead code elimination

On Sun, 6 Jul 2025 at 11:14, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Wed, 16 Apr 2025 at 13:42, Daniel Palmer <daniel@...f.com> wrote:
> > Allow the experimental dead code elimination config to be enabled.
> >
> > For my 68000 nommu config this frees up a few hundred K of memory
> > so seems worth while.
> >
> > Boot and build tested on nommu and mmu enabled configs.
> >
> > Before:
> > Memory: 5388K/8192K available (1986K kernel code, 114K rwdata,
> > 244K rodata, 92K init, 41K bss, 2624K reserved, 0K cma-reserved)
> >
> > After
> > Memory: 5684K/8192K available (1714K kernel code, 112K rwdata,
> > 228K rodata, 92K init, 37K bss, 2328K reserved, 0K cma-reserved)
> >
> > Signed-off-by: Daniel Palmer <daniel@...f.com>
>
> Thanks for your patch!
>
> Note that enabling this requires enabling CONFIG_EXPERT first, which is
> currently enabled in the Coldfire defconfigs, but not in the Classic
> defconfigs.  For atari_defconfig, I see a size reduction of ca. 150 KiB
> (gcc 13.3.0).

Let's share the actual figures I had saved before:

    $ bloat-o-meter vmlinux-v6.16-rc2+EXPERT{,+LD_DEAD_CODE_DATA_ELIMINATION}
    add/remove: 0/2125 grow/shrink: 10275/32 up/down: 52254/-205419 (-153165)
    [...]
    Total: Before=5277826, After=5124661, chg -2.90%

    dmesg:
    -Memory: 265412K/276480K available (4345K kernel code, 486K
rwdata, 1240K rodata, 164K init, 143K bss, 10440K reserved, 0K
cma-reserved)
    +Memory: 265616K/276480K available (4205K kernel code, 484K
rwdata, 1180K rodata, 160K init, 143K bss, 10236K reserved, 0K
cma-reserved)

    gcc version 13.3.0 (Ubuntu 13.3.0-6ubuntu2~24.04)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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