Messages in this thread | | | Subject | Re: [RFC PATCH v2] mm: migrate: Support multiple target nodes demotion | From | Baolin Wang <> | Date | Wed, 10 Nov 2021 09:30:11 +0800 |
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On 2021/11/10 8:47, Huang, Ying writes: > Baolin Wang <baolin.wang@linux.alibaba.com> writes: > >> On 2021/11/9 15:53, Huang, Ying writes: >>> Baolin Wang <baolin.wang@linux.alibaba.com> 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, 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@linux.alibaba.com> >>>> --- >>>> Changes from RFC v1: >>>> - Re-define the node_demotion structure. >>>> - Set up multiple target nodes by validating the node distance. >>>> - Add more comments. >>>> --- >>>> mm/migrate.c | 132 +++++++++++++++++++++++++++++++++++++++++++---------------- >>>> 1 file changed, 96 insertions(+), 36 deletions(-) >>>> >>>> diff --git a/mm/migrate.c b/mm/migrate.c >>>> index cf25b00..95f170d 100644 >>>> --- a/mm/migrate.c >>>> +++ b/mm/migrate.c >>>> @@ -1119,12 +1119,25 @@ 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 same class memory >>>> + * types. 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 +1148,13 @@ 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 DEMOTION_TARGET_NODES 15 >>>> +struct demotion_nodes { >>>> + unsigned short nr; >>>> + int nodes[DEMOTION_TARGET_NODES]; >>> Why we cannot use "unsigned short" for nodes[]? >> >> I think the default value of target node should be NUMA_NO_NODE(-1), >> so a signed type is more suitable. I can change to 'short' type. > > Yes. 'short' is better. > >>> >>>> +}; >>>> + >>>> +static struct demotion_nodes node_demotion[MAX_NUMNODES] __read_mostly; >>>> /** >>>> * next_demotion_node() - Get the next node in the demotion path >>>> @@ -1149,7 +1167,9 @@ static int __unmap_and_move(struct page *page, struct page *newpage, >>>> */ >>>> int next_demotion_node(int node) >>>> { >>>> - int target; >>>> + struct demotion_nodes *current_node_demotion = &node_demotion[node]; >>>> + int target, i; >>>> + nodemask_t target_nodes = NODE_MASK_NONE; >>>> /* >>>> * node_demotion[] is updated without excluding this >>>> @@ -1161,9 +1181,21 @@ int next_demotion_node(int node) >>>> * node_demotion[] reads need to be consistent. >>>> */ >>>> rcu_read_lock(); >>>> - target = READ_ONCE(node_demotion[node]); >>>> + for (i = 0; i < DEMOTION_TARGET_NODES; i++) { >>>> + target = READ_ONCE(current_node_demotion->nodes[i]); >>>> + if (target == NUMA_NO_NODE) >>>> + break; >>>> + >>>> + node_set(target, target_nodes); >>> Why do we need a nodemask? Why not just find a target node from >>> current_node_demotion->nodes[] randomly and directly? >> >> I think nodemask is scalable in future if we want to add more >> requirements to select the target node if necessary. Anyway now I have >> no strong preference with the nodemask, and can change to select the >> target node randomly and directly, which are something like below. >> >> + target_nr = READ_ONCE(current_node_demotion->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; >> + } >> + >> + target = READ_ONCE(current_node_demotion->nodes[index]); > > This looks generally OK. You may consider about memory order.
Yes. Sorry, I just cut out a piece of sample code. They are must under RCU lock, and using READ_ONCE() to avoid compiler reordering or read merging like the comments said.
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