linux-kernel - Re: [PATCH v4 0/4] MIPS: Modify mem= and memmap= parameter

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Date:   Sun, 6 Mar 2022 01:22:58 +0000 (GMT)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Mike Rapoport <rppt@...nel.org>
cc:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/4] MIPS: Modify mem= and memmap= parameter

On Sat, 5 Mar 2022, Mike Rapoport wrote:

> >  There's nothing to implement as the MIPS port has supported arbitrary 
> > memory maps since Dec 11th, 2000; that's almost 22 years now.  C.f.: 
> > <https://lore.kernel.org/linux-mips/Pine.GSO.3.96.1000814133957.7256S-100000@delta.ds2.pg.gda.pl/>, 
> > <https://git.kernel.org/pub/scm/linux/kernel/git/ralf/linux.git/commit/?id=97b7ae4257ef>.
> 
> You are right, and providing mem=X@Y for each contiguous memory range
> should work even after 22 years.
> I missed the fact that mem= can be repeated several times.

 Yep, I have now finally tracked down the original bootstrap log for the 
first try of that change:

This DECstation is a DS5000/2x0
Loading R[23]00 MMU routines.
CPU revision is: 00000230
Primary instruction cache 64kb, linesize 4 bytes
Primary data cache 64kb, linesize 4 bytes
Linux version 2.4.0-test5 (macro@...ro.ds2.pg.gda.pl) (gcc version 2.95.3 19991030 (prerelease)) #16 Sun Aug 13 16:43:22 CEST 2000
PROM-provided physical RAM map:
 memory: 06800000 @ 00000000
 memory: 00800000 @ 08000000
 memory: 00800000 @ 0a000000
User-defined physical RAM map:
 memory: 06800000 @ 00000000
 memory: 00800000 @ 08000000
 memory: 00800000 @ 0a000000
 memory: 00800000 @ 0c000000
On node 0 totalpages: 51200
zone(0): 51200 pages.
zone(1): 0 pages.
zone(2): 0 pages.
Kernel command line: rw console=ttyS2 mem=104M@0M mem=8M@...M mem=8M@...M mem=8M@...M
Calibrating delay loop... 39.85 BogoMIPS
Memory: 127852k/204800k available (2403k kernel code, 76948k reserved, 610k data, 72k init)
[...]

NB that system is still in service, with more RAM since added.

> >  Sadly commit a09fc446fb6d ("[MIPS] setup.c: use early_param() for early 
> > command line parsing") removed last pieces of inline documentation; I 
> > don't know why things like that get approved, but neither I can take 
> > responsibility.
> 
> This is sad indeed, but we still can update the kernel-parameters.txt with
> a MIPS paragraph.

 Sure, patches are welcome.

  Maciej