| Message ID | 20220123013537.20491-2-richard.weiyang@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] mm/page_alloc: add same penalty is enough to get round-robin order | expand |
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index f27afd517652..0cc25429a17e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6260,8 +6260,9 @@ static void build_zonelists(pg_data_t *pgdat) * So adding penalty to the first node in same * distance group to make it round-robin. */ - if (node_distance(local_node, node) != - node_distance(local_node, prev_node)) + if ((node_distance(local_node, node) != + node_distance(local_node, prev_node)) || + node == local_node) node_load[node] += nr_online_nodes; node_order[nr_nodes++] = node;
'Commit 54d032ced983 ("mm/page_alloc: use accumulated load when building node fallback list")' fix a bug on zonelist order. This let me think about what would happen if we have a node system with the following distance matrix. Node 0 1 2 3 4 5 6 7 ---------------------------- 0 10 12 12 12 32 32 32 32 1 12 10 12 12 32 32 32 32 2 12 12 10 12 32 32 32 32 3 12 12 12 10 32 32 32 32 4 32 32 32 32 10 12 12 12 5 32 32 32 32 12 10 12 12 6 32 32 32 32 12 12 10 12 7 32 32 32 32 12 12 12 10 Unfortunately for this case, the node fallback list gets built like this: Node Fallback list --------------------- 0: 0 1 2 3 4 5 6 7 1: 1 0 2 3 5 6 7 4 2: 2 3 0 1 6 7 4 5 3: 3 2 0 1 7 4 5 6 4: 4 5 6 7 0 1 2 3 5: 5 4 6 7 1 2 3 0 6: 6 7 4 5 2 3 0 1 7: 7 6 4 5 3 0 1 2 We found the order in diagonal block is not expected. The reason is we don't penalty local node. After penalty local node, the node fallback list gets built like this: Node Fallback list --------------------- 0: 0 1 2 3 4 5 6 7 1: 1 2 3 0 5 6 7 4 2: 2 3 0 1 6 7 4 5 3: 3 0 1 2 7 4 5 6 4: 4 5 6 7 0 1 2 3 5: 5 6 7 4 1 2 3 0 6: 6 7 4 5 2 3 0 1 7: 7 4 5 6 3 0 1 2 Now the fallback list is in round-robin order. I am not very familiar with the node distance pattern, while I tried the following distance matrix. Both of them works with this change. Node 0 1 2 3 ---------------- 0 10 10 10 10 1 10 10 10 10 2 10 10 10 10 3 10 10 10 10 Node 0 1 2 3 4 5 6 7 ---------------------------- 0 10 10 10 10 32 32 32 32 1 10 10 10 10 32 32 32 32 2 10 10 10 10 32 32 32 32 3 10 10 10 10 32 32 32 32 4 32 32 32 32 10 10 10 10 5 32 32 32 32 10 10 10 10 6 32 32 32 32 10 10 10 10 7 32 32 32 32 10 10 10 10 Signed-off-by: Wei Yang <richard.weiyang@gmail.com> CC: Krupa Ramakrishnan <krupa.ramakrishnan@amd.com> CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> CC: Michal Hocko <mhocko@suse.com> --- mm/page_alloc.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)