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memory_hotplug: introduce CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE

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This patchset continues the work I started with commit 31bc3858ea
("memory-hotplug: add automatic onlining policy for the newly added
memory").

Initially I was going to stop there and bring the policy setting logic
to userspace.  I met two issues on this way:

 1) It is possible to have memory hotplugged at boot (e.g.  with QEMU).
    These blocks stay offlined if we turn the onlining policy on by
    userspace.

 2) My attempt to bring this policy setting to systemd failed, systemd
    maintainers suggest to change the default in kernel or ...  to use
    tmpfiles.d to alter the policy (which looks like a hack to me):
        https://github.com/systemd/systemd/pull/2938

Here I suggest to add a config option to set the default value for the
policy and a kernel command line parameter to make the override.

This patch (of 2):

Introduce config option to set the default value for memory hotplug
onlining policy (/sys/devices/system/memory/auto_online_blocks).  The
reason one would want to turn this option on are to have early onlining
for hotpluggable memory available at boot and to not require any
userspace actions to make memory hotplug work.

[[email protected]: tweak Kconfig text]
Signed-off-by: Vitaly Kuznetsov <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: David Vrabel <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Igor Mammedov <[email protected]>
Cc: Lennart Poettering <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Vitaly Kuznetsov 2016-05-19 17:13:03 -07:00 • committed by Linus Torvalds
commit 8604d9e534
3 changed files with 25 additions and 4 deletions
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16
mm/Kconfig
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@ -192,6 +192,22 @@ config MEMORY_HOTPLUG_SPARSE
def_bool y
depends on SPARSEMEM && MEMORY_HOTPLUG
config MEMORY_HOTPLUG_DEFAULT_ONLINE
bool "Online the newly added memory blocks by default"
default n
depends on MEMORY_HOTPLUG
help
This option sets the default policy setting for memory hotplug
onlining policy (/sys/devices/system/memory/auto_online_blocks) which
determines what happens to newly added memory regions. Policy setting
can always be changed at runtime.
See Documentation/memory-hotplug.txt for more information.
Say Y here if you want all hot-plugged memory blocks to appear in
'online' state by default.
Say N here if you want the default policy to keep all hot-plugged
memory blocks in 'offline' state.
config MEMORY_HOTREMOVE
bool "Allow for memory hot remove"
select MEMORY_ISOLATION