On 06/01/2017 02:20 PM, Michal Hocko wrote: > From: Michal Hocko <mhocko@xxxxxxxx> > > movable_node kernel parameter allows to make hotplugable NUMA > nodes to put all the hotplugable memory into movable zone which > allows more or less reliable memory hotremove. At least this > is the case for the NUMA nodes present during the boot (see > find_zone_movable_pfns_for_nodes). > > This is not the case for the memory hotplug, though. > > echo online > /sys/devices/system/memory/memoryXYZ/status > > will default to a kernel zone (usually ZONE_NORMAL) unless the > particular memblock is already in the movable zone range which is not > the case normally when onlining the memory from the udev rule context > for a freshly hotadded NUMA node. The only option currently is to have a > special udev rule to echo online_movable to all memblocks belonging to > such a node which is rather clumsy. Not the mention this is inconsistent > as well because what ended up in the movable zone during the boot will > end up in a kernel zone after hotremove & hotadd without special care. Yeah, it would be better if movable_node worked consistently for both boot and runtime hotplug. > It would be nice to reuse memblock_is_hotpluggable but the runtime > hotplug doesn't have that information available because the boot and > hotplug paths are not shared and it would be really non trivial to > make them use the same code path because the runtime hotplug doesn't > play with the memblock allocator at all. > > Teach move_pfn_range that MMOP_ONLINE_KEEP can use the movable zone if > movable_node is enabled and the range doesn't overlap with the existing > normal zone. This should provide a reasonable default onlining strategy. > > Strictly speaking the semantic is not identical with the boot time > initialization because find_zone_movable_pfns_for_nodes covers only the > hotplugable range as described by the BIOS/FW. From my experience this > is usually a full node though (except for Node0 which is special and > never goes away completely). If this turns out to be a problem in the > real life we can tweak the code to store hotplug flag into memblocks > but let's keep this simple now. Simple should work, hopefully. - if memory is hotplugged, it's obviously hotplugable, so we don't have to rely on BIOS description. - there shouldn't be a reason to offline a non-removable (part of) node and online it back (which would move it from Normal to Movable after your patch?), right? Vlastimil -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
