Re: [PATCH v2 1/2] mm: migrate: Support multiple target nodes demotion

[Baolin Wang]

On 2021/11/11 16:20, Huang, Ying wrote:
> Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:
>
> > We have some machines with multiple memory types like below, which
> > have one fast (DRAM) memory node and two slow (persistent memory) memory
> > nodes. According to current node demotion policy, if node 0 fills up,
> > its memory should be migrated to node 1, when node 1 fills up, its
> > memory will be migrated to node 2: node 0 -> node 1 -> node 2 ->stop.
> >
> > But this is not efficient and suitbale memory migration route
> > for our machine with multiple slow memory nodes. Since the distance
> > between node 0 to node 1 and node 0 to node 2 is equal, and memory
> > migration between slow memory nodes will increase persistent memory
> > bandwidth greatly, which will hurt the whole system's performance.
> >
> > Thus for this case, we can treat the slow memory node 1 and node 2
> > as a whole slow memory region, and we should migrate memory from
> > node 0 to node 1 and node 2 if node 0 fills up.
> >
> > This patch changes the node_demotion data structure to support multiple
> > target nodes, and establishes the migration path to support multiple
> > target nodes with validating if the node distance is the best or not.
> >
> > available: 3 nodes (0-2)
> > node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
> > node 0 size: 62153 MB
> > node 0 free: 55135 MB
> > node 1 cpus:
> > node 1 size: 127007 MB
> > node 1 free: 126930 MB
> > node 2 cpus:
> > node 2 size: 126968 MB
> > node 2 free: 126878 MB
> > node distances:
> > node   0   1   2
> >    0:  10  20  20
> >    1:  20  10  20
> >    2:  20  20  10
> >
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > ---
> >   mm/migrate.c | 138 +++++++++++++++++++++++++++++++++++++++++++----------------
> >   1 file changed, 102 insertions(+), 36 deletions(-)
> >
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index cf25b00..126e9e6 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -50,6 +50,7 @@
> >   #include <linux/ptrace.h>
> >   #include <linux/oom.h>
> >   #include <linux/memory.h>
> > +#include <linux/random.h>
> >   
> >   #include <asm/tlbflush.h>
> >   
> > @@ -1119,12 +1120,25 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> >    *
> >    * This is represented in the node_demotion[] like this:
> >    *
> > - *	{  1, // Node 0 migrates to 1
> > - *	   2, // Node 1 migrates to 2
> > - *	  -1, // Node 2 does not migrate
> > - *	   4, // Node 3 migrates to 4
> > - *	   5, // Node 4 migrates to 5
> > - *	  -1} // Node 5 does not migrate
> > + *	{  nr=1, nodes[0]=1 }, // Node 0 migrates to 1
> > + *	{  nr=1, nodes[0]=2 }, // Node 1 migrates to 2
> > + *	{  nr=0, nodes[0]=-1 }, // Node 2 does not migrate
> > + *	{  nr=1, nodes[0]=4 }, // Node 3 migrates to 4
> > + *	{  nr=1, nodes[0]=5 }, // Node 4 migrates to 5
> > + *	{  nr=0, nodes[0]=-1 }, // Node 5 does not migrate
> > + *
> > + * Moreover some systems may have multiple slow memory nodes.
> > + * Suppose a system has one socket with 3 memory nodes, node 0
> > + * is fast memory type, and node 1/2 both are slow memory
> > + * type, and the distance between fast memory node and slow
> > + * memory node is same. So the migration path should be:
> > + *
> > + *	0 -> 1/2 -> stop
> > + *
> > + * This is represented in the node_demotion[] like this:
> > + *	{ nr=2, {nodes[0]=1, nodes[1]=2} }, // Node 0 migrates to node 1 and node 2
> > + *	{ nr=0, nodes[0]=-1, }, // Node 1 dose not migrate
> > + *	{ nr=0, nodes[0]=-1, }, // Node 2 does not migrate
> >    */
> >   
> >   /*
> > @@ -1135,8 +1149,13 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> >    * must be held over all reads to ensure that no cycles are
> >    * observed.
> >    */
> > -static int node_demotion[MAX_NUMNODES] __read_mostly =
> > -	{[0 ...  MAX_NUMNODES - 1] = NUMA_NO_NODE};
> > +#define DEFAULT_DEMOTION_TARGET_NODES 15
> > +struct demotion_nodes {
> > +	unsigned short nr;
> > +	short nodes[DEFAULT_DEMOTION_TARGET_NODES];
> > +};
> > +
> > +static struct demotion_nodes node_demotion[MAX_NUMNODES] __read_mostly;
> >   
> >   /**
> >    * next_demotion_node() - Get the next node in the demotion path
> > @@ -1149,6 +1168,8 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> >    */
> >   int next_demotion_node(int node)
> >   {
> > +	struct demotion_nodes *nd = &node_demotion[node];
> > +	unsigned short target_nr, index;
> >   	int target;
> >   
> >   	/*
> > @@ -1161,9 +1182,25 @@ int next_demotion_node(int node)
> >   	 * node_demotion[] reads need to be consistent.
> >   	 */
> >   	rcu_read_lock();
> > -	target = READ_ONCE(node_demotion[node]);
> > -	rcu_read_unlock();
> > +	target_nr = READ_ONCE(nd->nr);
> > +
> > +	if (target_nr == 0) {
> > +		target = NUMA_NO_NODE;
> > +		goto out;
> > +	} else if (target_nr == 1) {
> > +		index = 0;
> > +	} else {
> > +		/*
> > +		 * If there are multiple target nodes, just select one
> > +		 * target node randomly.
> > +		 */
> > +		index = get_random_int() % target_nr;
> > +	}
>
> How about use "switch" here?

Sure, will do. Thanks.