summaryrefslogtreecommitdiffstats
path: root/Documentation
diff options
context:
space:
mode:
authorBaoquan He <bhe@redhat.com>2020-04-06 20:06:50 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-07 10:43:40 -0700
commitf3cd4c865b8ad61ff6dc61feba759a98ca06f039 (patch)
treee8f7199d2b193383e8cfda63ea45e636ad52285c /Documentation
parentdccacf8def2b718528754867b58b37734b59b0d7 (diff)
downloadlinux-f3cd4c865b8ad61ff6dc61feba759a98ca06f039.tar.bz2
mm/memory_hotplug.c: only respect mem= parameter during boot stage
In commit 357b4da50a62 ("x86: respect memory size limiting via mem= parameter") a global varialbe max_mem_size is added to store the value parsed from 'mem= ', then checked when memory region is added. This truly stops those DIMMs from being added into system memory during boot-time. However, it also limits the later memory hotplug functionality. Any DIMM can't be hotplugged any more if its region is beyond the max_mem_size. We will get errors like: [ 216.387164] acpi PNP0C80:02: add_memory failed [ 216.389301] acpi PNP0C80:02: acpi_memory_enable_device() error [ 216.392187] acpi PNP0C80:02: Enumeration failure This will cause issue in a known use case where 'mem=' is added to the hypervisor. The memory that lies after 'mem=' boundary will be assigned to KVM guests. After commit 357b4da50a62 merged, memory can't be extended dynamically if system memory on hypervisor is not sufficient. So fix it by also checking if it's during boot-time restricting to add memory. Otherwise, skip the restriction. And also add this use case to document of 'mem=' kernel parameter. Fixes: 357b4da50a62 ("x86: respect memory size limiting via mem= parameter") Signed-off-by: Baoquan He <bhe@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Juergen Gross <jgross@suse.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: William Kucharski <william.kucharski@oracle.com> Cc: David Hildenbrand <david@redhat.com> Cc: Balbir Singh <bsingharora@gmail.com> Link: http://lkml.kernel.org/r/20200204050643.20925-1-bhe@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt13
1 files changed, 11 insertions, 2 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2d31d811a52d..86aae1fa099a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2573,13 +2573,22 @@
For details see: Documentation/admin-guide/hw-vuln/mds.rst
mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
- Amount of memory to be used when the kernel is not able
- to see the whole system memory or for test.
+ Amount of memory to be used in cases as follows:
+
+ 1 for test;
+ 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.
+
[X86] Work as limiting max address. Use together
with memmap= to avoid physical address space collisions.
Without memmap= PCI devices could be placed at addresses
belonging to unused RAM.
+ Note that this only takes effects during boot time since
+ in above case 3, memory may need be hot added after boot
+ if system memory of hypervisor is not sufficient.
+
mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
memory.