* Michael Ellerman <mpe@xxxxxxxxxxxxxx> [2020-03-13 21:48:06]: > Sachin Sant <sachinp@xxxxxxxxxxxxxxxxxx> writes: > >> The patch below might work. Sachin can you test this? I tried faking up > >> a system with a memoryless node zero but couldn't get it to even start > >> booting. > >> > > The patch did not help. The kernel crashed during > > the boot with the same call trace. > > > > BUG_ON() introduced with the patch was not triggered. > > OK, that's weird. > > I eventually managed to get a memoryless node going in sim, and it > appears to work there. > > eg in dmesg: > > [ 0.000000][ T0] numa: NODE_DATA [mem 0x2000fffa2f80-0x2000fffa7fff] > [ 0.000000][ T0] numa: NODE_DATA(0) on node 1 > [ 0.000000][ T0] numa: NODE_DATA [mem 0x2000fff9df00-0x2000fffa2f7f] > ... > [ 0.000000][ T0] Early memory node ranges > [ 0.000000][ T0] node 1: [mem 0x0000000000000000-0x00000000ffffffff] > [ 0.000000][ T0] node 1: [mem 0x0000200000000000-0x00002000ffffffff] > [ 0.000000][ T0] Could not find start_pfn for node 0 > [ 0.000000][ T0] Initmem setup node 0 [mem 0x0000000000000000-0x0000000000000000] > [ 0.000000][ T0] On node 0 totalpages: 0 > [ 0.000000][ T0] Initmem setup node 1 [mem 0x0000000000000000-0x00002000ffffffff] > [ 0.000000][ T0] On node 1 totalpages: 131072 > > # dmesg | grep set_numa > [ 0.000000][ T0] set_numa_mem: mem node for 0 = 1 > [ 0.005654][ T0] set_numa_mem: mem node for 1 = 1 > > So is the problem more than just node zero having no memory? > The problem would happen with possible nodes which are not yet present. i.e no cpus, no memory attached to those nodes. Please look at http://lore.kernel.org/lkml/20200312131438.GB3277@xxxxxxxxxxxxxxxxxx/t/#u for more details. The summary being: pgdat/Node_Data for such nodes is not allocated. Hence the node_present_pages(nid) called where nid is a possible but not yet present node fails. Currently node_present_pages(nid) and node_to_mem_node don't seem to be equipped to handle possible but not present nodes. > cheers -- Thanks and Regards Srikar Dronamraju
