linux-kernel - Re: [PATCH] mm/hotplug: Only respect mem= parameter during boot stage

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Date:   Tue, 10 Dec 2019 22:05:34 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, jgross@...e.com,
        william.kucharski@...cle.com, mingo@...nel.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH] mm/hotplug: Only respect mem= parameter during boot stage

On 12/10/19 at 02:32pm, Michal Hocko wrote:
> On Tue 10-12-19 20:55:57, Baoquan He wrote:
> [...]
> > Btw, as you said at above, I am confused by the '[KNL,BOOT]', what does
> > the 'BOOT' mean in the documentation of 'mem='? I checked all parameters
> > with 'BOOT', still don't get it clearly.
> 
> This is a good question indeed. I have checked closer and this is what
> documentation says
> Documentation/admin-guide/kernel-parameters.rst
> "
>         BOOT    Is a boot loader parameter.
> 
> Parameters denoted with BOOT are actually interpreted by the boot
> loader, and have no meaning to the kernel directly.
> "
> 
> and that really doesn't fit, right? So I went to check the full history
> git tree just to get to 2.4.0-test5 and no explanation whatsoever.
> Fun, isn't it? ;)

Yeah, very interesting. Finally I got their original purpose from
Documentation/x86/boot.rst.

Special Command Line Options
============================

If the command line provided by the boot loader is entered by the
user, the user may expect the following command line options to work.
They should normally not be deleted from the kernel command line even
though not all of them are actually meaningful to the kernel.  Boot
loader authors who need additional command line options for the boot
loader itself should get them registered in
Documentation/admin-guide/kernel-parameters.rst to make sure they will not
conflict with actual kernel options now or in the future.

...

So here, [KNL,BOOT], KNL means it's used for kernel, BOOT means it's
needed by boot loader.

I think we should at least add a note in kernel-parameters.txt to
explain this. Will add it.

Thanks
Baoquan