linux-kernel - Re: [for-next][PATCH 04/26] bootconfig: Add Extra Boot Config support

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Date:   Fri, 7 Feb 2020 22:17:28 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [for-next][PATCH 04/26] bootconfig: Add Extra Boot Config
 support

Hi Geert,

On Fri, 7 Feb 2020 09:49:02 +0100
Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> Hi Hiramatsu-san,
> 
> On Fri, Feb 7, 2020 at 1:30 AM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > On Thu, 6 Feb 2020 18:20:15 +0100
> > Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > On Thu, Feb 6, 2020 at 3:42 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > > > On Thu, 6 Feb 2020 12:54:05 +0100
> > > > Borislav Petkov <bp@...en8.de> wrote:
> > > > > On Tue, Jan 14, 2020 at 04:03:20PM -0500, Steven Rostedt wrote:
> > > > > > diff --git a/init/Kconfig b/init/Kconfig
> > > > > > index a34064a031a5..63450d3bbf12 100644
> > > > > > --- a/init/Kconfig
> > > > > > +++ b/init/Kconfig
> > > > > > @@ -1215,6 +1215,17 @@ source "usr/Kconfig"
> > > > > >
> > > > > >  endif
> > > > > >
> > > > > > +config BOOT_CONFIG
> > > > > > +   bool "Boot config support"
> > > > > > +   select LIBXBC
> > > > > > +   default y
> > > > >
> > > > > Any particular reason this is default y? Why should it be enabled by
> > > > > default on all boxes?
> > > >
> > > > Oh, you are not the first person asked that :)
> > > >
> > > > https://lkml.org/lkml/2019/12/9/563
> > > >
> > > > And yes, I think this is important that will useful for most developers
> > > > and admins. Since the bootconfig already covers kernel and init options,
> > > > this can be a new standard way to pass args to kernel boot.
> > > >
> > > > And as I reported above thread, the memory footpoint of view, most code
> > > > and working memory are released after boot. Also, as Linus's suggested,
> > > > now this feature is enabled only if user gives "bootconfig" on the kernel
> > > > command line. So the side effect is minimized.
> > >
> > > With m68k/atari_defconfig, bloat-o-meter says:
> > >
> > >     add/remove: 39/0 grow/shrink: 2/0 up/down: 13086/0 (13086)
> > >
> > > which is IMHO not that small for a "default y" option that may or may not
> > > be used.
> > >
> > > Especially:
> > >
> > >         Function                                     old     new   delta
> > >     xbc_nodes                                      -    8192   +8192
> > >
> > > Any chance xbc_nodes can be allocated dynamically, and only when needed?
> >
> > Yes, I think we can use memblock to allocate it. However, this xbc_nodes is
> 
> Good.
> 
> > __init_data, which is released right after boot. So I think it should be
> > OK except for your system doesn't have user space...
> 
> __initdata is still part of the kernel image (note that we no longer
> have __initbss) and consumes RAM early on, and is thus subject to e.g.
> bootloader[1] and platform limitations (e.g. the kernel must fit in the
> first block of physical memory).
> So trying to avoid large static arrays is useful.

OK, I'll replace it with memblock. Then it will be 5 - 6KB in total.

Thank you!


-- 
Masami Hiramatsu <mhiramat@...nel.org>