Messages in this thread | | | Date | Fri, 21 Feb 2014 15:57:48 -0800 | From | Nishanth Aravamudan <> | Subject | Re: [PATCH] mm: exclude memory less nodes from zone_reclaim |
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On 21.02.2014 [14:07:35 -0800], Andrew Morton wrote: > On Thu, 20 Feb 2014 10:51:44 +0100 Michal Hocko <mhocko@suse.cz> wrote: > > > We had a report about strange OOM killer strikes on a PPC machine > > although there was a lot of swap free and a tons of anonymous memory > > which could be swapped out. In the end it turned out that the OOM was > > a side effect of zone reclaim which wasn't doesn't unmap and swapp out > > and so the system was pushed to the OOM. Although this sounds like a bug > > somewhere in the kswapd vs. zone reclaim vs. direct reclaim interaction > > numactl on the said hardware suggests that the zone reclaim should > > have been set in the first place: > > node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 > > node 0 size: 0 MB > > node 0 free: 0 MB > > node 2 cpus: > > node 2 size: 7168 MB > > node 2 free: 6019 MB > > node distances: > > node 0 2 > > 0: 10 40 > > 2: 40 10 > > > > So all the CPUs are associated with Node0 which doesn't have any memory > > while Node2 contains all the available memory. Node distances cause an > > automatic zone_reclaim_mode enabling. > > > > Zone reclaim is intended to keep the allocations local but this doesn't > > make any sense on the memory less nodes. So let's exclude such nodes > > for init_zone_allows_reclaim which evaluates zone reclaim behavior and > > suitable reclaim_nodes. > > > > ... > > > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1855,7 +1855,7 @@ static void __paginginit init_zone_allows_reclaim(int nid) > > { > > int i; > > > > - for_each_online_node(i) > > + for_each_node_state(i, N_MEMORY) > > if (node_distance(nid, i) <= RECLAIM_DISTANCE) > > node_set(i, NODE_DATA(nid)->reclaim_nodes); > > else > > @@ -4901,7 +4901,8 @@ void __paginginit free_area_init_node(int nid, unsigned long *zones_size, > > > > pgdat->node_id = nid; > > pgdat->node_start_pfn = node_start_pfn; > > - init_zone_allows_reclaim(nid); > > + if (node_state(nid, N_MEMORY)) > > + init_zone_allows_reclaim(nid); > > #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP > > get_pfn_range_for_nid(nid, &start_pfn, &end_pfn); > > #endif > > What happens if someone later hot-adds some memory to that node?
This probably isn't a very good answer, but I think the question of how to support a node that starts off memoryless and then gets memory hot-added later is still open. But this at least gets us further and would be needed anyways, I think.
I'm going to try and look at the hot-add component after we get this base stuff in, if that's ok, but it's definitely on my todo list.
Thanks, Nish
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