memory_hotplug: introduce CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE
This patchset continues the work I started with commit 31bc3858 ("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. [akpm@linux-foundation.org: tweak Kconfig text] Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Dan Williams <dan.j.williams@intel.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: David Rientjes <rientjes@google.com> Cc: Igor Mammedov <imammedo@redhat.com> Cc: Lennart Poettering <lennart@poettering.net> Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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