From: Dave Hansen <[email protected]>
Prepare for the kernel to auto-migrate pages to other memory nodes with a user defined node migration table. This allows creating single migration target for each NUMA node to enable the kernel to do NUMA page migrations instead of simply reclaiming colder pages. A node with no target is a "terminal node", so reclaim acts normally there. The migration target does not fundamentally _need_ to be a single node, but this implementation starts there to limit complexity. If you consider the migration path as a graph, cycles (loops) in the graph are disallowed. This avoids wasting resources by constantly migrating (A->B, B->A, A->B ...). The expectation is that cycles will never be allowed. Signed-off-by: Dave Hansen <[email protected]> Cc: Yang Shi <[email protected]> Cc: David Rientjes <[email protected]> Cc: Huang Ying <[email protected]> Cc: Dan Williams <[email protected]> --- b/mm/migrate.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff -puN mm/migrate.c~0006-node-Define-and-export-memory-migration-path mm/migrate.c --- a/mm/migrate.c~0006-node-Define-and-export-memory-migration-path 2020-06-29 16:34:36.849312609 -0700 +++ b/mm/migrate.c 2020-06-29 16:34:36.853312609 -0700 @@ -1159,6 +1159,29 @@ out: return rc; } +static int node_demotion[MAX_NUMNODES] = {[0 ... MAX_NUMNODES - 1] = NUMA_NO_NODE}; + +/** + * next_demotion_node() - Get the next node in the demotion path + * @node: The starting node to lookup the next node + * + * @returns: node id for next memory node in the demotion path hierarchy + * from @node; -1 if @node is terminal + */ +int next_demotion_node(int node) +{ + get_online_mems(); + while (true) { + node = node_demotion[node]; + if (node == NUMA_NO_NODE) + break; + if (node_online(node)) + break; + } + put_online_mems(); + return node; +} + /* * gcc 4.7 and 4.8 on arm get an ICEs when inlining unmap_and_move(). Work * around it. _
