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

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

[Mike Rapoport]

From: Mike Rapoport <rppt@linux.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@linux.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
 
 			[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.
 
-- 
2.34.1

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

[Randy Dunlap]

Hi Mike,

On 3/9/22 04:24, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.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@linux.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?

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

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

[Sergey Shtylyov]

On 3/9/22 3:24 PM, Mike Rapoport wrote:

> From: Mike Rapoport <rppt@linux.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@linux.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

   Used?

> to set the memory size, there is

   What? :-)

[...]

MBR, Sergey

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

[Mike Rapoport]

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@linux.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@linux.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.