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authorDavid Hildenbrand <david@redhat.com>2021-11-05 23:44:46 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-11-06 23:30:42 +0300
commite14b41556d9ec20af60a9f672ac6f64dd450763c (patch)
treeaeea89afb1b7819929bba39994629ebc6381fa26 /include/linux/memblock.h
parent53d38316ab2017a7c0d733765b521700aa357ec9 (diff)
downloadlinux-e14b41556d9ec20af60a9f672ac6f64dd450763c.tar.xz
memblock: improve MEMBLOCK_HOTPLUG documentation
The description of MEMBLOCK_HOTPLUG is currently short and consequently misleading: we're actually dealing with a memory region that might get hotunplugged later (i.e., the platform+firmware supports it), yet it is indicated in the firmware-provided memory map as system ram that will just get used by the system for any purpose when not taking special care. The firmware marked this memory region as a hot(un)plugged (e.g., hotplugged before reboot), implying that it might get hotunplugged again later. Whether we consider this information depends on the "movable_node" kernel commandline parameter: only with "movable_node" set, we'll try keeping this memory hotunpluggable, for example, by not serving early allocations from this memory region and by letting the buddy manage it using the ZONE_MOVABLE. Let's make this clearer by extending the documentation. Note: kexec *has to* indicate this memory to the second kernel. With "movable_node" set, we don't want to place kexec-images on this memory. Without "movable_node" set, we don't care and can place kexec-images on this memory. In both cases, after successful memory hotunplug, kexec has to be re-armed to update the memory map for the second kernel and to place the kexec-images somewhere else. Link: https://lkml.kernel.org/r/20211004093605.5830-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Eric Biederman <ebiederm@xmission.com> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Jianyong Wu <Jianyong.Wu@arm.com> Cc: Jiaxun Yang <jiaxun.yang@flygoat.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Shahab Vahedi <shahab@synopsys.com> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Vineet Gupta <vgupta@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/memblock.h')
-rw-r--r--include/linux/memblock.h6
1 files changed, 5 insertions, 1 deletions
diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 484650681bee..1d2b3e902a84 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -28,7 +28,11 @@ extern unsigned long long max_possible_pfn;
/**
* enum memblock_flags - definition of memory region attributes
* @MEMBLOCK_NONE: no special request
- * @MEMBLOCK_HOTPLUG: hotpluggable region
+ * @MEMBLOCK_HOTPLUG: memory region indicated in the firmware-provided memory
+ * map during early boot as hot(un)pluggable system RAM (e.g., memory range
+ * that might get hotunplugged later). With "movable_node" set on the kernel
+ * commandline, try keeping this memory region hotunpluggable. Does not apply
+ * to memblocks added ("hotplugged") after early boot.
* @MEMBLOCK_MIRROR: mirrored region
* @MEMBLOCK_NOMAP: don't add to kernel direct mapping and treat as
* reserved in the memory map; refer to memblock_mark_nomap() description