linux-kernel - Re: [PATCH] docs/kernel-parameters: update description of mem=

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Date:   Wed, 9 Mar 2022 18:56:32 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-doc@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] docs/kernel-parameters: update description of mem=

On Wed, Mar 09, 2022 at 08:05:05AM -0800, Randy Dunlap wrote:
> Hi Mike,
> 
> On 3/9/22 04:24, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@...ux.ibm.com>
> > 
> > The existing description of mem= does not cover all the cases and
> > differences between how architectures treat it.
> > 
> > Extend the description to match the code.
> > 
> > Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> > ---
> > 
> > This is in a way a followup for the discussion of mem= usage on MIPS:
> > 
> > https://lore.kernel.org/all/1646461289-31992-1-git-send-email-yangtiezhu@loongson.cn
> > 
> >  .../admin-guide/kernel-parameters.txt         | 20 +++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> > 
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index f5a27f067db9..f3597841a031 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2834,6 +2834,15 @@
> >  			2 when the kernel is not able to see the whole system memory;
> >  			3 memory that lies after 'mem=' boundary is excluded from
> >  			 the hypervisor, then assigned to KVM guests.
> > +			4 to limit the memory available for kdump kernel.
> > +
> > +			[ARC,MICROBLAZE] - the limit applies only to low memory,
> > +			high memory is not affected.
> > +
> > +			[ARM64] - only limits memory covered by the linear
> > +			mapping. The NOMAP regions are not affected.
> > +
> > +			[HEXAGON] - must be use to set the memory size, there is
> 
> Above line seems to be missing something?

Yes :)
 
> Otherwise looks good AFAIK.
> 
> >  
> >  			[X86] Work as limiting max address. Use together
> >  			with memmap= to avoid physical address space collisions.
> > @@ -2844,6 +2853,17 @@
> >  			in above case 3, memory may need be hot added after boot
> >  			if system memory of hypervisor is not sufficient.
> >  
> > +	mem=nn[KMG]@ss[KMG]
> > +			[ARM,MIPS] - override the memory layout reported by
> > +			firmware.
> > +			Define a memory region of size nn[KMG] starting at
> > +			ss[KMG].
> > +			Multiple different regions can be specified with
> > +			multiple mem= parameters on the command line.
> > +
> > +	mem=nn[KMG]	[HEXAGON] Set the memory size.
> > +			Must be specified, otherwise memory size will be 0.
> > +
> >  	mem=nopentium	[BUGS=X86-32] Disable usage of 4MB pages for kernel
> >  			memory.
> >  
> 
> -- 
> ~Randy

-- 
Sincerely yours,
Mike.