On Wed, Oct 16, 2019 at 03:11:49PM -0700, Dave Hansen wrote:
>
> From: Keith Busch <keith.busch@xxxxxxxxx>
>
> 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, and this rule is enforced if the user tries to make
> such a cycle.
>
> Signed-off-by: Keith Busch <keith.busch@xxxxxxxxx>
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> ---
>
> b/drivers/base/node.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++++
> b/include/linux/node.h | 6 ++++
> 2 files changed, 79 insertions(+)
>
> diff -puN drivers/base/node.c~0003-node-Define-and-export-memory-migration-path drivers/base/node.c
> --- a/drivers/base/node.c~0003-node-Define-and-export-memory-migration-path 2019-10-16 15:06:55.895952599 -0700
> +++ b/drivers/base/node.c 2019-10-16 15:06:55.902952599 -0700
> @@ -101,6 +101,10 @@ static const struct attribute_group *nod
> NULL,
> };
>
> +#define TERMINAL_NODE -1
Wouldn't we have a confusion with NUMA_NO_NODE, which is also -1?
> +static int node_migration[MAX_NUMNODES] = {[0 ... MAX_NUMNODES - 1] = TERMINAL_NODE};
This is the first time is see range initializer in kernel code. It is GCC
extension. Do we use it anywhere already?
Many distributions compile kernel with NODES_SHIFT==10, which means this
array will take 4k even on single node machine.
Should it be dynamic?
> +static DEFINE_SPINLOCK(node_migration_lock);
> +
> static void node_remove_accesses(struct node *node)
> {
> struct node_access_nodes *c, *cnext;
> @@ -530,6 +534,74 @@ static ssize_t node_read_distance(struct
> }
> static DEVICE_ATTR(distance, S_IRUGO, node_read_distance, NULL);
>
> +static ssize_t migration_path_show(struct device *dev,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + return sprintf(buf, "%d\n", node_migration[dev->id]);
> +}
> +
> +static ssize_t migration_path_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int i, err, nid = dev->id;
> + nodemask_t visited = NODE_MASK_NONE;
> + long next;
> +
> + err = kstrtol(buf, 0, &next);
> + if (err)
> + return -EINVAL;
> +
> + if (next < 0) {
Any negative number to set it to terminal node? Why not limit it to -1?
We may find use for user negative numbers later.
> + spin_lock(&node_migration_lock);
> + WRITE_ONCE(node_migration[nid], TERMINAL_NODE);
> + spin_unlock(&node_migration_lock);
> + return count;
> + }
> + if (next >= MAX_NUMNODES || !node_online(next))
> + return -EINVAL;
What prevents offlining after the check?
> + /*
> + * Follow the entire migration path from 'nid' through the point where
> + * we hit a TERMINAL_NODE.
> + *
> + * Don't allow loops migration cycles in the path.
> + */
> + node_set(nid, visited);
> + spin_lock(&node_migration_lock);
> + for (i = next; node_migration[i] != TERMINAL_NODE;
> + i = node_migration[i]) {
> + /* Fail if we have visited this node already */
> + if (node_test_and_set(i, visited)) {
> + spin_unlock(&node_migration_lock);
> + return -EINVAL;
> + }
> + }
> + WRITE_ONCE(node_migration[nid], next);
> + spin_unlock(&node_migration_lock);
> +
> + return count;
> +}
> +static DEVICE_ATTR_RW(migration_path);
> +
> +/**
> + * next_migration_node() - Get the next node in the migration path
> + * @current_node: The starting node to lookup the next node
> + *
> + * @returns: node id for next memory node in the migration path hierarchy from
> + * @current_node; -1 if @current_node is terminal or its migration
> + * node is not online.
> + */
> +int next_migration_node(int current_node)
> +{
> + int nid = READ_ONCE(node_migration[current_node]);
> +
> + if (nid >= 0 && node_online(nid))
> + return nid;
> + return TERMINAL_NODE;
> +}
> +
> static struct attribute *node_dev_attrs[] = {
> &dev_attr_cpumap.attr,
> &dev_attr_cpulist.attr,
> @@ -537,6 +609,7 @@ static struct attribute *node_dev_attrs[
> &dev_attr_numastat.attr,
> &dev_attr_distance.attr,
> &dev_attr_vmstat.attr,
> + &dev_attr_migration_path.attr,
> NULL
> };
> ATTRIBUTE_GROUPS(node_dev);
> diff -puN include/linux/node.h~0003-node-Define-and-export-memory-migration-path include/linux/node.h
> --- a/include/linux/node.h~0003-node-Define-and-export-memory-migration-path 2019-10-16 15:06:55.898952599 -0700
> +++ b/include/linux/node.h 2019-10-16 15:06:55.902952599 -0700
> @@ -134,6 +134,7 @@ static inline int register_one_node(int
> return error;
> }
>
> +extern int next_migration_node(int current_node);
> extern void unregister_one_node(int nid);
> extern int register_cpu_under_node(unsigned int cpu, unsigned int nid);
> extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid);
> @@ -186,6 +187,11 @@ static inline void register_hugetlbfs_wi
> node_registration_func_t unreg)
> {
> }
> +
> +static inline int next_migration_node(int current_node)
> +{
> + return -1;
> +}
> #endif
>
> #define to_node(device) container_of(device, struct node, dev)
> _
>
--
Kirill A. Shutemov
