| Message ID | 20211004093605.5830-3-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/memory_hotplug: full support for add_memory_driver_managed() with CONFIG_ARCH_KEEP_MEMBLOCK | expand |
On Mon, Oct 04, 2021 at 11:36:02AM +0200, David Hildenbrand wrote: > 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. > > Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> > --- > include/linux/memblock.h | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/include/linux/memblock.h b/include/linux/memblock.h > index 34de69b3b8ba..4ee8dd2d63a7 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 > -- > 2.31.1 >
diff --git a/include/linux/memblock.h b/include/linux/memblock.h index 34de69b3b8ba..4ee8dd2d63a7 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
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. Signed-off-by: David Hildenbrand <david@redhat.com> --- include/linux/memblock.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)