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mm, memory_hotplug: drop artificial restriction on online/offline
Patch series "remove CONFIG_MOVABLE_NODE". I am continuing to clean up the memory hotplug code and CONFIG_MOVABLE_NODE seems dubious at best. The following two patches simply removes the flag and make it de-facto always enabled. The current semantic of the config option is twofold 1) it automatically binds hotplugable nodes to have memory in zone_movable by default when movable_node is enabled 2) forbids memory hotplug to online all the memory as movable when !CONFIG_MOVABLE_NODE. The later restriction is quite dubious because there is no clear cut of how much normal memory do we need for a reasonable system operation. A single memory block which is sufficient to allow further movable onlines is far from sufficient (e.g a node with >2GB and memblocks 128MB will fill up this zone with struct pages leaving nothing for other allocations). Removing the config option will not only reduce the configuration space it also removes quite some code. The semantic of the movable_node command line parameter is preserved. The first patch removes the restriction mentioned above and the second one simply removes all the CONFIG_MOVABLE_NODE related stuff. The last patch moves movable_node flag handling to memory_hotplug proper where it belongs. [1] http://lkml.kernel.org/r/20170524122411.25212-1-mhocko@kernel.org This patch (of 3): Commit 74d42d8f ("memory_hotplug: ensure every online node has NORMAL memory") has introduced a restriction that every numa node has to have at least some memory in !movable zones before a first movable memory can be onlined if !CONFIG_MOVABLE_NODE. Likewise can_offline_normal checks the amount of normal memory in !movable zones and it disallows to offline memory if there is no normal memory left with a justification that "memory-management acts bad when we have nodes which is online but don't have any normal memory". While it is true that not having _any_ memory for kernel allocations on a NUMA node is far from great and such a node would be quite subotimal because all kernel allocations will have to fallback to another NUMA node but there is no reason to disallow such a configuration in principle. Besides that there is not really a big difference to have one memblock for ZONE_NORMAL available or none. With 128MB size memblocks the system might trash on the kernel allocations requests anyway. It is really hard to draw a line on how much normal memory is really sufficient so we have to rely on administrator to configure system sanely therefore drop the artificial restriction and remove can_offline_normal and can_online_high_movable altogether. Link: http://lkml.kernel.org/r/20170529114141.536-2-mhocko@kernel.org Signed-off-by:Michal Hocko <mhocko@suse.com> Acked-by: