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docs/kernel-parameters: update description of mem=

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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>
Link: https://lore.kernel.org/r/20220310082736.1346366-1-rppt@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mike Rapoport
2022-03-10 10:27:36 +02:00
committed by Jonathan Corbet
parent c01c2e435d
commit 75c05fabb8
1 changed files with 18 additions and 0 deletions
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18
Documentation/admin-guide/kernel-parameters.txt
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@@ -2827,6 +2827,9 @@
For details see: Documentation/admin-guide/hw-vuln/mds.rst For details see: Documentation/admin-guide/hw-vuln/mds.rst
mem=nn[KMG] [HEXAGON] Set the memory size.
Must be specified, otherwise memory size will be 0.
mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
Amount of memory to be used in cases as follows: Amount of memory to be used in cases as follows:
@@ -2834,6 +2837,13 @@
2 when the kernel is not able to see the whole system memory; 2 when the kernel is not able to see the whole system memory;
3 memory that lies after 'mem=' boundary is excluded from 3 memory that lies after 'mem=' boundary is excluded from
the hypervisor, then assigned to KVM guests. 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.
[X86] Work as limiting max address. Use together [X86] Work as limiting max address. Use together
with memmap= to avoid physical address space collisions. with memmap= to avoid physical address space collisions.
@@ -2844,6 +2854,14 @@
in above case 3, memory may need be hot added after boot in above case 3, memory may need be hot added after boot
if system memory of hypervisor is not sufficient. 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=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
memory. memory.