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Date:   Mon, 5 Oct 2020 01:40:47 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@linux-mips.org>
To:     Baoquan He <bhe@redhat.com>
cc:     Huacai Chen <chenhc@lemote.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Eric Biederman <ebiederm@xmission.com>,
        Dave Young <dyoung@redhat.com>,
        Vivek Goyal <vgoyal@redhat.com>,
        "open list:MIPS" <linux-mips@vger.kernel.org>,
        kexec@lists.infradead.org, Fuxin Zhang <zhangfx@lemote.com>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>
Subject: Re: [PATCH 1/3] MIPS: Crash kernel should be able to see old
 memories
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On Sat, 3 Oct 2020, Maciej W. Rozycki wrote:

> > Interesting. Seems MIPS does support mem=X@Y, even though the document
> > of 'mem=' says it's used to specify amount of memory, but not memory
> > region. Anyway, leave this to mips reviewers, thanks for replying.
> > 
> > ~~~~~~~~~~~~~~~~~~~
> >         mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
> >                         Amount of memory to be used in cases as follows:
> 
>  Yep, I implemented it for the DECstation back in 2000:
> 
> commit 97b7ae4257ef7ba8ed9b7944a4f56a49af3e8abb
> Author: Ralf Baechle <ralf@linux-mips.org>
> Date:   Mon Dec 11 16:41:05 2000 +0000
> 
>     Memmap fixes from Maciej.
> 
> (from the LMO repo) in line with the x86 syntax.  I don't know why it 
> hasn't ever been documented in "Kernel Parameters" (for any port), but I'm 
> fairly sure it has been somewhere.

 Self-correction: documentation used to be there, but was removed around 
Linux 2.5.65:

commit 041a679cb20e4fcb841665b09cf7c6d24ab4ad39
Author: Ralf Baechle <ralf@linux-mips.org>
Date:   Thu Jun 5 00:04:28 2003 +0000

    Merge with Linux 2.5.65.

(same repo) as the parameter was renamed to `memmap=' in the x86 port.  
Obviously whoever did that did not bother to check other ports, even 
though the parameter was marked (and `memmap=' still is) generic.

  Maciej