From: Huang Ying ying.huang@intel.com
commit fc89213a636c3735eb3386f10a34c082271b4192 upstream.
In commit ac16ec835314 ("mm: migrate: support multiple target nodes demotion"), after the first demotion target node is found, we will continue to check the next candidate obtained via find_next_best_node(). This is to find all demotion target nodes with same NUMA distance. But one side effect of find_next_best_node() is that the candidate node returned will be set in "used" parameter, even if the candidate node isn't passed in the following NUMA distance checking, the candidate node will not be used as demotion target node for the following nodes. For example, for system as follows,
node distances: node 0 1 2 3 0: 10 21 17 28 1: 21 10 28 17 2: 17 28 10 28 3: 28 17 28 10
when we establish demotion target node for node 0, in the first round node 2 is added to the demotion target node set. Then in the second round, node 3 is checked and failed because distance(0, 3) > distance(0, 2). But node 3 is set in "used" nodemask too. When we establish demotion target node for node 1, there is no available node. This is wrong, node 3 should be set as the demotion target of node 1.
To fix this, if the candidate node is failed to pass the distance checking, it will be cleared in "used" nodemask. So that it can be used for the following node.
The bug can be reproduced and fixed with this patch on a 2 socket server machine with DRAM and PMEM.
Link: https://lkml.kernel.org/r/20220128055940.1792614-1-ying.huang@intel.com Fixes: ac16ec835314 ("mm: migrate: support multiple target nodes demotion") Signed-off-by: "Huang, Ying" ying.huang@intel.com Reviewed-by: Baolin Wang baolin.wang@linux.alibaba.com Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Zi Yan ziy@nvidia.com Cc: Oscar Salvador osalvador@suse.de Cc: Yang Shi shy828301@gmail.com Cc: zhongjiang-ali zhongjiang-ali@linux.alibaba.com Cc: Xunlei Pang xlpang@linux.alibaba.com Cc: Mel Gorman mgorman@techsingularity.net Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/migrate.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
--- a/mm/migrate.c +++ b/mm/migrate.c @@ -3085,18 +3085,21 @@ static int establish_migrate_target(int if (best_distance != -1) { val = node_distance(node, migration_target); if (val > best_distance) - return NUMA_NO_NODE; + goto out_clear; }
index = nd->nr; if (WARN_ONCE(index >= DEMOTION_TARGET_NODES, "Exceeds maximum demotion target nodes\n")) - return NUMA_NO_NODE; + goto out_clear;
nd->nodes[index] = migration_target; nd->nr++;
return migration_target; +out_clear: + node_clear(migration_target, *used); + return NUMA_NO_NODE; }
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