* Vlastimil Babka <vbabka@xxxxxxx> [2020-03-12 14:51:38]: > > * Vlastimil Babka <vbabka@xxxxxxx> [2020-03-12 10:30:50]: > > > >> On 3/12/20 9:23 AM, Sachin Sant wrote: > >> >> On 12-Mar-2020, at 10:57 AM, Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx> wrote: > >> >> * Michal Hocko <mhocko@xxxxxxxxxx> [2020-03-11 12:57:35]: > >> >>> On Wed 11-03-20 16:32:35, Srikar Dronamraju wrote: > >> >>>> To ensure a cpuless, memoryless dummy node is not online, powerpc need > >> >>>> to make sure all possible but not present cpu_to_node are set to a > >> >>>> proper node. > >> >>> > >> >>> Just curious, is this somehow related to > >> >>> http://lkml.kernel.org/r/20200227182650.GG3771@xxxxxxxxxxxxxx? > >> >>> > >> >> > >> >> The issue I am trying to fix is a known issue in Powerpc since many years. > >> >> So this surely not a problem after a75056fc1e7c (mm/memcontrol.c: allocate > >> >> shrinker_map on appropriate NUMA node"). > >> >> > > > > While I am not an expert in the slub area, I looked at the patch > > a75056fc1e7c and had some thoughts on why this could be causing this issue. > > > > On the system where the crash happens, the possible number of nodes is much > > greater than the number of onlined nodes. The pdgat or the NODE_DATA is only > > available for onlined nodes. > > > > With a75056fc1e7c memcg_alloc_shrinker_maps, we end up calling kzalloc_node > > for all possible nodes and in ___slab_alloc we end up looking at the > > node_present_pages which is NODE_DATA(nid)->node_present_pages. > > i.e for a node whose pdgat struct is not allocated, we are trying to > > dereference. > > From what we saw, the pgdat does exist, the problem is that slab's per-node data > doesn't exist for a node that doesn't have present pages, as it would be a waste > of memory. Just to be clear Before my 3 patches to fix dummy node: srikar@ltc-zzci-2 /sys/devices/system/node $ cat $PWD/possible 0-31 srikar@ltc-zzci-2 /sys/devices/system/node $ cat $PWD/online 0-1 > > Uh actually you are probably right, the NODE_DATA doesn't exist anymore? In > Sachin's first report [1] we have > > [ 0.000000] numa: NODE_DATA [mem 0x8bfedc900-0x8bfee3fff] > [ 0.000000] numa: NODE_DATA(0) on node 1 > [ 0.000000] numa: NODE_DATA [mem 0x8bfed5200-0x8bfedc8ff] > So even if pgdat would exist for nodes 0 and 1, there is no pgdat for the rest 30 nodes. > But in this thread, with your patches Sachin reports: and with my patches srikar@ltc-zzci-2 /sys/devices/system/node $ cat $PWD/possible 0-31 srikar@ltc-zzci-2 /sys/devices/system/node $ cat $PWD/online 1 > > [ 0.000000] numa: NODE_DATA [mem 0x8bfedc900-0x8bfee3fff] > so we only see one pgdat. > So I assume it's just node 1. In that case, node_present_pages is really dangerous. > > [1] > https://lore.kernel.org/linux-next/3381CD91-AB3D-4773-BA04-E7A072A63968@xxxxxxxxxxxxxxxxxx/ > > > Also for a memoryless/cpuless node or possible but not present nodes, > > node_to_mem_node(node) will still end up as node (atleast on powerpc). > > I think that's the place where this would be best to fix. > Maybe. I thought about it but the current set_numa_mem semantics are apt for memoryless cpu node and not for possible nodes. We could have upto 256 possible nodes and only 2 nodes (1,2) with cpu and 1 node (1) with memory. node_to_mem_node seems to return what is set in set_numa_mem(). set_numa_mem() seems to say set my numa_mem node for the current memoryless node to the param passed. But how do we set numa_mem for all the other 253 possible nodes, which probably will have 0 as default? Should we introduce another API such that we could update for all possible nodes? > > I tried with this hunk below and it works. > > > > But I am not sure if we need to check at other places were > > node_present_pages is being called. > > I think this seems to defeat the purpose of node_to_mem_node()? Shouldn't it > return only nodes that are online with present memory? > CCing Joonsoo who seems to have introduced this in ad2c8144418c ("topology: add > support for node_to_mem_node() to determine the fallback node") > Agree > I think we do need well defined and documented rules around node_to_mem_node(), > cpu_to_node(), existence of NODE_DATA, various node_states bitmaps etc so > everyone handles it the same, safe way. > Other option would be to tweak Kirill Tkhai's patch such that we call kvmalloc_node()/kzalloc_node() if node is online and call kvmalloc/kvzalloc if the node is offline. > > diff --git a/mm/slub.c b/mm/slub.c > > index 626cbcbd977f..bddb93bed55e 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -2571,9 +2571,13 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, > > if (unlikely(!node_match(page, node))) { > > int searchnode = node; > > > > - if (node != NUMA_NO_NODE && !node_present_pages(node)) > > - searchnode = node_to_mem_node(node); > > - > > + if (node != NUMA_NO_NODE) { > > + if (!node_online(node) || !node_present_pages(node)) { > > + searchnode = node_to_mem_node(node); > > + if (!node_online(searchnode)) > > + searchnode = first_online_node; > > + } > > + } > > if (unlikely(!node_match(page, searchnode))) { > > stat(s, ALLOC_NODE_MISMATCH); > > deactivate_slab(s, page, c->freelist, c); -- Thanks and Regards Srikar Dronamraju
